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Class
BOILERS
THE POWER HANDBOOKS
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-SOLD SEPARATELY OR IN SETS
BY PROF. AUGUSTUS H. GILL
OF THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY
ENGINE ROOM CHEMISTRY
BY HUBERT E. COLLINS
BOILERS KNOCKS AND KINKS
SHAFT GOVERNORS PUMPS
ERECTING WORK SHAFTING, PULLEYS AND
PIPES AND PIPING BELTING
BY F. E. MATTHEWS
REFRIGERATION. (In Preparation.)
HILL PUBLISHING COMPANY
505 PEARL STREET, NEW YORK
6 BOUVERIE STREET, LONDON, E. C.
THE POWER HANDBOOKS
BOILERS
COMPILED AND WRITTEN
BY
HUBERT E. COLLINS
OF TM.;
' Of
1908
HILL PUBLISHING COMPANY
505 PEARL STREET, NEW YORK
6 BOUVERIE STREET, LONDON, E.G.
American Machinist Power The Engineering and Mining Journal
Copyright, 1908, BY THE HILL PUBLISHING COMPANY
All rights reserved
Hill Publishing Company, New York, U.S.A.
INTRODUCTION
THIS volume endeavors to furnish the reader with
much new and valuable material on an old subject,
together with much standard information which every
engineer likes to have at his hand. A glance at the
chapter headings will show the scope of the book.
It will be seen that the subject is pretty fully covered
from the working conditions inside of a boiler to simple
talks on the various phases of boiler practice. It
also covers the design of boiler furnaces for wood burn-
ing, and much other useful material.
One very important feature is the portion on the
safety valve based on Mr. Fred R. Low's supplement
to Power on that subject. The author is indebted to
Mr. Low for permission to incorporate this material
in the book, and to various other contributors, whose
articles have been used as a whole or in part in the
work. ^ ^
HUBERT E. COLLINS.
NEW YORK, November ; 1908.
196487
CONTENTS
CHAP. PAGE
I WATCHING A BOILER AT WORK i
II SIMPLE TALK ON EFFICIENCY OF RIVETED JOINTS n
III SIMPLE TALK ON THE BURSTING STRENGTH OF
BOILERS 17
IV SIMPLE TALK ON THE BURSTING STRENGTH OF
BOILERS 24
V SIMPLE TALK ON THE BRACING OF HORIZONTAL RE-
TURN TUBULAR BOILERS 30
VI CALCULATING THE STRENGTH OF RIVETED JOINTS . 40
VII To FIND THE AREA TO BE BRACED IN THE HEADS OF
HORIZONTAL TUBULAR BOILERS 67
VIII GRAPHICAL DETERMINATION OF BOILER DIMENSIONS 70
IX THE SAFETY VALVE 75
X HORSE-POWER OF BOILERS 120
XI BOILER APPLIANCES AND THEIR INSTALLATION . 123
XII CARE OF THE HORIZONTAL TUBULAR BOILER . . 133
XIII CARE AND MANAGEMENT OF BOILERS .... 145
XIV SETTING RETURN TUBULAR BOILERS .... 150
XV RENEWING TUBES IN A TUBULAR BOILER ... . 156
XVI USE OF W'OOD AS FUEL FOR STEAM BOILERS . . . 161
XVII BOILER RULES 179
XVIII MECHANICAL TUBE CLEANERS 184
vii
WATCHING A BOILER AT WORK 1
IF we take a test-tube filled with water nearly to
the top and hold it over a Bunsen flame, the water
boils violently and overflows the tube. This violent
over-boiling is due to the conflicting action of the
ascending and descending currents of steam and water
in the tube. On the other hand, if we take a tube
shaped like a U, the arms of which are connected
together at the top, fill it with water^and place one leg
of the U in the flame, a direct circulation soon com-
mences. The water passes along in one direction and
the steam is liberated at the surface. In this case
there is very little violent ebullition, because there
are no counter currents and the steam is discharged
quietly over a liberal surface.
Desiring to ascertain just how nearly a boiler could
be designed to work upon the U-tube principle of
circulation, after several trials the model boiler
shown in Fig. i was produced.
This model was built entirely of brass. It contained
three drums four inches in diameter and 120 brass
tubes one-quarter of an inch in diameter. The tubes
were connected into headers and into the circum-
1 Contributed to Power by C. Hill Smith.
I
BOILERS
ferences of the drums. The heads of all three drums
were made of plate glass, for observation of the in-
terior of the boiler when making steam. It will be
noted that the design of the boiler closely resembles
FIG. i.
the U shape, only that one leg is considerably longer
than the other, and there are two legs on the side of
the U where the heat is applied.
Each of the three drums serves a special function
WATCHING A BOILER AT WORK 3
which will be noted from the description of the experi-
ments. The two legs, instead of being connected
together at the top, as was the case in the U-tube, are
connected by two separate passages, one for the water
to pass through and the other for the steam.
In preparing for the tests the boiler was mounted
on a stand, so that the tubes inclined from the hori-
zontal 20 degrees, and the whole was enclosed on all
sides by brass plates. Alcohol lamps were placed
inside the casing at a point to correspond with the
regular location of grates, or at about one-fourth of
the distance between the front headers and the rear
drum. The steam outlet was located on the rear
drum, as was the safety valve, for experimental
reasons, although in actual practice the safety valve
would be located on the front drum. The feed-pipe
was introduced in the rear drum, while the blow-off
entered the lowest point of the lower drum, which we
will call the mud-drum. The boiler was attached to
an open condenser.
The boiler being ready for test, it was filled with
cold water until the upper drums were filled to one-
half their volume. Candles were placed behind one
head of each of the three drums for the purpose of
lighting the inside. The alcohol lamps were then
lighted and the boiler interior was ready to observe
through the glass heads of the drums.
The first action noted was in the front drum, which
served as a discharge chamber for all the steaming
tubes. The tubes of the lower bank discharged into
it through headers, while those of the upper bank dis-
4 BOILERS
charged into it independently. Many faint, oily-white
streamers were seen to rise from the nipples connecting
the headers to the front drum, passing upward to the
surface of the drum. They resembled little streamers
of white smoke. On reaching the surface of the water
they passed into the horizontal circulating tubes
which connected the two upper drums. These little
streamers were heated water, which, being lighter than
the water in the drum, rose to the surface. This same
action soon appeared from the ends of the upper bank
of tubes, the little streamers rising in a similar manner
and passing into the horizontal tubes.
By observing the rear drum, the little streamers
could be seen coming into this drum from the front
drum. Here they turned downward into the vertical
tubes which connected the rear drum to the rear
headers and the mud-drum. No action could be
noted in the mud-drum, which fact seemed to indicate
that these currents of water passed into the upper
tubes and thence into the front drum again, as the
action from these tubes appeared very much more
decided than the action from the nipples, notwithstand-
ing the fact that the lower tubes were nearer to the
flame than the upper ones. This was undoubtedly
due to the fact that the heated currents of water
remained as near the surface as possible, while the
colder water passed to the bottom of the boiler, hav-
ing greater specific gravity.
Particles of sediment could be seen coming down
the vertical circulating tubes into the mud-drum,
evidently precipitated from the water that was being
WATCHING A BOILER AT WORK 5
heated. This sediment passed to the bottom of the
drum, where it remained. A very gradual action was
now noted in the mud-drum in the nature of similar
currents of water coming down the vertical tubes.
These currents acted strangely on entering the drum;
they spread out on coming in contact with the colder
and denser water lying at the bottom. By placing
the finger on the upper portion of the glass head and
then on the lower, quite a difference in temperature
was noted. Little streamers of heated water soon
commenced to pass into the lower bank of streaming
tubes which were connected into this drum. They
passed across the drum with a sort of shivering motion.
A new and very interesting phenomenon was now
noticed. Occasionally there would appear from the
ends of the steaming tubes little rings of heated water,
which shot across the drum with considerable velocity.
The action in the front drum became very much
more pronounced and air bubbles appeared from the
nipples and tubes. The boiler was circulating water
with great rapidity in the same direction and it was
noticed, by placing the hand on different parts of the
boiler, that all parts were of the same temperature.
The air bubbles now discharged in great quantities
from the tubes and nipples and rising to the surface
disturbed the water level considerably. It was noted
that they floated along under the surface of the water
before they broke.
Gradually these air bubbles ceased to appear and a
new kind took their places. The latter were steam
bubbles and they discharged into the drum with greater
6 BOILERS
velocity than the former. On reaching the surface
of the water they broke immediately, but they agi-
tated the water level to a much greater extent. Foun-
tains of water would shoot up into the drum for quite
a distance and showed very vividly the conditions
present in the shell type of boiler, where there are no
defined paths for the water and steam to travel and
nothing to prevent their conflict with each other.
This also shows the cause for wet steam, and the great
danger of entraining water with steam, as is the case
where the steam is removed from the same place
where violent ebullition is present.
While the water level in the front drum was violently
agitated, the water level in the rear drum remained
perfectly calm. No steam was generated in this drum,
as the horizontal tubes connecting it to the front
drum only circulated water that had been freed of its
steam.
As the steam gage soon registered a pressure of 9
pounds, the main stop-valve was opened to allow the
steam to flow to the condenser. The abrupt release
of pressure caused the water to expand suddenly and
the water level rose about one-quarter of an inch. This
was evidently due to the sudden generation of steam
caused by the drop in the pressure. This increased
ebullition caused a very violent action in the front
drum and the circulation of water through the boiler
increased greatly in velocity. The nipples and tubes
in the front drum discharged great quantities of
bubbles. The water level in the rear drum during
this increase in ebullition showed but a few ripples,
WATCHING A BOILER AT WORK 7
which were evidently due to the vibration of the steam
passing into the steam main, or the discharge into the
water of the open condenser.
The sudden generation of steam caused by the
opening of the steam valve and subsequent reduction
in pressure, it is believed, explains how the partial
rupture of the shell of a return-tubular boiler is ad-
vanced to a disastrous explosion by the unexpected
increased generation of steam due to the lowered
pressure.
The steam main was now closed sufficiently to allow
the boiler to operate on a constant pressure of about 6
pounds. It operated very smoothly under these con-
ditions and made a very interesting sight with the
steam generating in the front drum, where the nipples
and tubes discharged great quantities of bubbles.
The action in the mud-drum had in the meantime
become well worth watching. In the other two drums
the water showed clear in the candle light, but the
color of the water in the mud-drum was very murky.
Particles of sediment were noted settling to the bottom.
The withdrawal of water from this drum by the steam-
ing tubes did not appear to draw this sediment into
the tubes, as the drum was of ample size so that the
suction was not felt at the bottom where the sediment
deposited. This emphasized clearly the advantage
of a very large mud-drum to allow of the thorough
settling of the sediment.
The condition of the front drum was thought to be
too violent for good practice, because the ebullition
indicated restriction of circulation. The boiler was
8 BOILERS
put out of operation for the purpose of making changes
in this drum to prevent extreme ebullition. The glass
heads were removed and other nipples inserted over
the nipples that connected the headers into the drum,
it being here that the most violent discharge of steam
was discernible. These new nipples were cut long
enough to reach to the water level, or just a trifle
below it.
The glass heads were replaced and the boiler put in
operation again. The circulation was similar to that
in the first test, and no real difference was noted until
the boiler commenced to make steam. Then it was
seen that the ebullition in this drum was considerably
reduced, the agitation that remained being caused
by the discharge from the tubes of the upper bank.
This reduction was evidently due to having provided
a channel through which the water and steam from
the nipples might flow to the surface of the water and
so prevent contact with the water in the drum. As
the steam and water no longer had to force their way
to the surface, the disturbance of the water level was
naturally reduced entirely in this direction. The water
rose from the nipples in little fountains, the steam
disengaging from it in the upper part of the drum.
The boiler was operated under very severe condi-
tions to try the value of this addition of nipples. The
main stop-valve was suddenly opened after a consider-
able steam pressure was obtained. It had very little
effect on the water level in this drum, only causing
the nipples to discharge fountains of water quite a
distance into the drum. No water was thrown into
WATCHING A BOILER AT WORK 9
the superheating tubes, as the fountains of water dis-
charged vertically and fell back immediately to the
water level.
The value of this attachment being proved, the
boiler was blown down, and after the water was all
withdrawn from the boiler considerable sediment was
found in the bottom of the lower or mud-drum. No-
where else was sediment found, as the drums offered no
opportunities for the sediment to settle, being pierced
at their lowest points by tubes and nipples. The tubes
were inclined 20 degrees, which insured thorough
draining of the boiler.
From the foregoing experiments many points of
great value for improvement in design of water-tube
boilers can be derived. The violent ebullition in the
front drum shows conclusively that steam should not
be withdrawn from the boiler at a point where ebulli-
tion is present, on account of the danger of getting
water entrained with the steam. It also shows that
any sudden reduction of the pressure causes violent
ebullition and priming. The front-drum conditions
show that this is a good place to locate the safety valve,
as the sudden opening of it would cause no liability
of priming if the steam is not withdrawn from this
drum.
The total lack of any ebullition in the rear drum
shows that this is an ideal spot to remove the steam.
It was noted that, owing to the large amount of sepa-
rating surface provided, the opening of the steam
valve caused no priming in this drum. Another fea-
ture to be noted is the value of a large mud-drum to
I0 BOILERS
provide ample opportunity for the sediment to settle,
and also to provide a large supply of water for the
bottom tubes. It would be impossible to force the
boiler hard enough to drain this drum of water, so
the danger of burning out these tubes is eliminated.
The provision of the long nipples in the front drum
proved the advantage of providing separate passages
to allow the steam and water to reach the surface of
the water, thus obviating the necessity of their forcing
their way to the surface through the large body of
water in this drum and so cause violent ebullition.
II
SIMPLE TALK ON EFFICIENCY OF
RIVETED JOINTS
MATTER is conceived to be composed of myriads of
tiny molecules separated from each other by distances
which are very considerable as compared with their
diameters, and held in fixed relation to each other in
solid bodies, by such an attraction as holds the earth
to the sun or the moon to the earth. When we tear a
piece of boiler sheet apart it is the attraction of these
molecules which we are overcoming, and if the metal is
uniform the force required to separate it will depend
upon the surface which we expose. It will take twice
as much force to pull the larger of the two bars in Fig. 2
apart as it will the smaller, because there is twice as
much surface exposed at B as at A, and the attrac-
tion of twice as many molecules to overcome.
The force tending to pull a body apart in this way
is called a "tensile" force, and the resistance to the
force necessary to pull a piece apart is called its "ulti-
mate tensile strength." This is usually given in pounds
per square inch, and is for boiler iron around 45,000
and for boiler steel around 60,000 pounds. It should be
found stamped on the sheets of which boilers are made.
Suppose we have a single riveted joint like Fig. 3. We
12
BOILERS
FIG. 2.
can divide it into strips as by the dotted lines half-
way between the rivets, and consider one of these strips,
for since they are all alike, what is true of one will be
true of all. The width of each strip will be the same as
FIG. 3.
EFFICIENCY OF RIVETED JOINTS 13
the distance from center to center of the rivets. This is
called the "pitch." Let us suppose the pitch to be 2\
inches, the diameter of the rivet I inch, the thickness of
the plate i inch, the tensile strength of the plate 60,000
and the shearing strength of the rivets 43,000 pounds.
FIG. 4.
There are two ways in which this joint can fail: by
tearing the sheet apart where there is the least of it to
break, as at a a a a, Fig. 3, or by shearing the rivet as
in Fig. 4.
If the strip were whole as at A in Fig. 5, it would have
2j X i = 1.125 square inches
of section, and since it takes 60,000 pounds to pull one
square inch apart it would take
1.125 X 60,000 = 67,500 pounds
to separate it.
I 4 BOILERS
But i inch of the sheet has been cut out for the rivet,
so that there are left only
2\ - i == ij inches
of width to be separated, and
il X i = 0.625 square inch
of area. This would stand a pull of only
0.625 X 60,000 = 37,500 pounds.
Whether the joint will part by tearing the sheet or
shearing the rivet depends, of course, on which is the
stronger. The rivet has
i X i X 0.7854 = 0.7854 square inch
of area, and it takes 49,000 pounds to shear each square
inch, so that it would take a pull of
0.7854 X 49,000 = 38,484.6 pounds.
to shear the rivet.
It is evident that the rivets would go, then, long
before the plate, and that the strength of. the joint
would be o o /- /-
38,484.6 -f- 67,500 = 0.57
or 57 per cent, of the strength of the full plate.
But we can add to the rivet strength without reducing
the plate strength by putting in another row of rivets
behind the first row. In Fig. 6 two rivets have to be
sheared, doubling the rivet strength without reducing
the plate strength, for the holes for these extra rivets
do not reduce the plate section along any one line if
there is space enough between the rows. In Fig. 7 the
EFFICIENCY OF RIVETED JOINTS 15
sheet is no more apt to part along the line aaaa than
it would be if the second row of rivets were not there,
and no more likely to part on the line bbbb than on the
other. Any strip of a width equal to the pitch will
FIG. 6.
contain two rivets, whether we take it through the
rivet centers, as at A, Fig. 7, or at equal distance to
either side of one rivet in each row,'as at B in the same
figure. In the first case it includes one full rivet and
two halves, and in the latter case two full rivets.
FIG. 7.
To find the efficiency of this joint, then, we calculate
the efficiencies of the plate and use the lowest efficiency.
To calculate the plate efficiency, divide the difference
1 6 BOILERS
between the pitch and the diameter of the rivets by the
pitch.
This is simpler than the operation which we went
through above, which was
(pitch-diam.) X thickness X tensile strength
pitch X thickness X tensile strength
the numerator being the pull required to separate the
sheet with the rivet holes cut out, and the denominator
the pull required to separate the full sheet. As the
thickness and tensile strength appear in both numerator
and denominator, they cancel out.
To find the rivet efficiency, multiply the diameter of
the rivet by itself, by 0.7854, by the shearing strength per
square inch and by the number of rows, and divide by
the product of the pitch, thickness and tensile strength
per square inch of section.
These rules are applicable only to lap joints where
the rivets are in single shear.
Ill
SIMPLE TALKS ON THE BURSTING STRENGTH
OF BOILERS
THERE are two ways that a shell, such as is shown
in the sketches herewith, might break under internal
pressure. The sheets might tear lengthwise, letting
the shell separate, as in Fig. 8, or they might tear
across, letting it separate endwise, as in Fig. 9.
8095 i't*
80956 1C
V^
FIG. 8.
FIG. 9.
Which is it the more likely to do?
To push it apart endwise, as in Fig. 9, we have the
force acting on the heads. This force is the pressure
per square inch multiplied by the number of square
inches in the head. The area of a circle is the diam-
eter multiplied by itself and by 3.1416 and divided by
4; or since 3.1416 divided by 4 is .7854, the area is the
square of the diameter multiplied by .7854.
17
l8 BOILERS
Suppose the internal diameter of the shell to be 48
inches, and the pressure 100 pounds per square inch,
the pressure on each head would be
48 X 48 X .7854 X 100 = 180,956.16 pounds,
or over 90 tons. This pressure would act on each head,
and the effect would be the same as though two weights
of 180,956.16 pounds each were pulling against each
other through the boiler, as in Fig. 10.
FIG. 10.
If the shell were not heavy enough to stand the
strain, it would tear apart along the line where the
metal happened to be the weakest, as at A. At first
sight it looks as though the metal had to sustain both
these forces or weights, and that the stress upon the
shell would be twice 180,956.16 pounds; but a little
consideration will show that this is not so. One simply
furnishes the equal and opposite action with which
every force must bje resisted. A man pulling against
a boy on a rope (Fig. 1 1) can pull no harder than the
boy pulls against him. If he does he will pull the boy
off his feet, and the strain on the rope will be only
what one of them pulls, not the sum of both pulls.
In order that the man may pull with a force of 50
BURSTING STRENGTH OF BOILERS 19
pounds, the boy must hold against him with a force
of 50 pounds. Both are pulling with a force of 50
pounds, but the tension on the rope is 50 pounds, not
100. The boy might be replaced with a post (Fig. 12).
Now, when the man pulls with a force of 50 pounds
FIG. 12.
against the post, you would not say that there was
100 pounds tension on the rope; yet the post is pulling
or holding against him with a force of 50 pounds,
2O
BOILERS
just as the boy did. In Fig. 13 it is easily seen that
the tension on the cord is 50 pounds. You would not
say that it was 100, if the pull of the weight were
resisted by another weight of 50 pounds, as in Fig. 14,
instead of by the floor.
v
I 50 Ib 3 . I
FIG. 13.
FIG. 14.
The shell is therefore in the case which we have
imagined subjected to a force of 180,956.16 pounds,
which tends to pull it apart endwise, as in Fig. 10.
To resist this there are as many running inches of
shell as there are inches in the circumference.
The circumference is 3.1416 times the diameter, so
that to pull the boiler in two
48 X 3.1416 = 1 50.7968 inches
of sheet would have to be pulled apart.
The force exerted upon each running inch of sheet
would be the pressure acting endwise divided by the
circumference, or
180,956.16 4- 150.7968 = i, 200 pounds.
The area is
diam. X diam. X 3.1416
4
BURSTING STRENGTH OF BOILERS 21
The circumference is
Diam. X 3.1416.
Dividing the area by the circumference we have
diam. X diam. X 3.1416 _ diam.
4 X diam. X 3.1416 4
or the strain on each running inch of sheet per pound
of pressure is one-fourth the diameter.
-Diamoter-
FIG. 15.
Now let us see what it would be in the other direc-
tion.
If we consider the pressure acting in all directions
as in the upper half of Fig. 15, we should, to get the
total pressure on the area, have to multiply the pres-
22 BOILERS
sure per square inch by the whole area, which would
be the circumference for a. strip i inch wide; but if
we are considering the effect of pressure in one direc-
tion only, we must consider only the area in that
direction. If we are studying the effect of the pres-
sure in forcing the shell in the direction of the arrows
in the lower half of Fig. 15, we must consider only the
area which comes crosswise to that direction, the
"projected area," as it is called; the area which the
piece would present if we were to hold it up and look
at it in the direction of the arrows or of the shadow
which it would cast in rays of light running in the
direction of the pressure. This, it will be easily recog-
FIG. 1 6.
nized, is the diameter of the boiler wide and i inch
high, as shown in Fig. 15, so that the number of square
inches upon which the pressure is effective in one
direction is equal to the diameter for a strip i inch
wide. There is therefore a force tending to pull each
i -inch ring of the shell apart, as in Fig. 16, of 48 X 100
= 4800 pounds, and as this force is resisted by two
running inches of metal, one at/4 and one at B (Fig. i 5),
BURSTING STRENGTH OF BOILERS 23
the stress per inch will be 4800 ~ 2 = 2400 pounds.
This is just twice what we found it to be in the other
direction; and it is plain that this should be so, for
the stress per pound of pressure tending to burst the
boiler, as in Fig. 8, is, as we have just seen,
diam.
which is just twice the - - which we found it to be
in the other direction. It is for this reason that boilers
are double riveted along the side or longitudinal
seams, while single riveting is good enough for girth
seams.
IV
SIMPLE TALKS ON THE BURSTING
STRENGTH OF BOILERS
IN the preceding chapter we found that a cylinder
equally strong all over, will split lengthwise with one-
half the pressure which would be needed to tear it
apart endwise.
FIG. 17.
Let us see how much pressure it would take to burst
a shell of this kind. We will consider a strip i inch in
width, as in Fig. 17, for the action upon all the similar
strips into which the boiler can be imagined to be
spaced off will be the same. We see that the pressure
24
BURSTING STRENGTH OF BOILERS 25
tending to pull the ring, i inch in width, apart is equal
to the pressure per square inch multiplied by the
diameter of the ring. The total pressure in all direc-
tions, acts on the circumference as shown by the radial
arrows at the upper portion of the cut, but when we
come to consider the force acting in one direction we
must take the projected area in that direction; the area
of the shadow, as explained before, cast by rays of light
flowing in that direction, and that area would be that
of the strip as we see it at the top of Fig. 17, i inch
wide and the diameter of the boiler long.
It is sometimes hard for one to see why the diameter
is used here, instead of the circumference, and a
further illustration is here given.
FIG. 18.
Suppose you had a piston in an engine cylinder
made in steps like Fig. 18. This would have a good
deal more surface to rust or to condense steam than
would a flat piston, but it would have no more effec-
tive area for the production of power, would it? One
hundred pounds behind it in the cylinder would push
no harder on the crosshead with this than with a per-
fectly flat piston; because the sidewise pressure against
26
BOILERS
the steps is balanced by an equal pressure from the
opposite side; only the pressure on the flat rings effec-
tive to move the piston forward, and the area of all
these rings added together, is just the same as that of
a flat surface of the same external diameter, as seen by
the projection at the right.
FIG. 19.
This would be just as true if the steps were a millionth
or a hundred-millionth of an inch wide and high instead
of an inch or more, so that it is just as true of a conical
surface, like Fig. 19, as of Fig. 18, or of a concave
surface, like Fig. 20, as of either; and it is evident that
it is the flattened-out area which one sees in looking
at the object in the line of the force considered, the
projected area in that direction as it is called, and not
the real superficial area which is effective.
BURSTING STRENGTH OF BOILERS 27
We have then a force equal to the pressure per square
inch multiplied by the internal diameter of the shell
tending to pull each inch in length of it apart, and we
have two sections, A and B, Fig. 15, where the sheet
must part.
The force tending to tear eacb of these is the pressure
per square inch multiplied by the radius, or half the
diameter of the shell. The resistance that the piece
of shell will offer to being torn apart is the tensile
strength per square inch multiplied by the number of
square inches to be torn apart.
FIG. 21.
This area is one inch long and the thickness of the
sheet in width. The area in square inches is therefore
the same as the thickness in inches. If the plate were
f of an inch thick, for example, its section per inch of
length would be f of a square inch, as shown in Fig. 21.
The two opposing forces, which must be equal, not
only at the point of fracture, but at all times, are:
Pressure per square inch X radius, and pull per
square inch X thickness.
The pull on the sheet is called the tensile force. If
we want to find the tensile force on the sheet for any
pressure per square inch, we multiply that pressure by
28 BOILERS
the radius and divide by the thickness of the sheet in
inches.
If we want to find the pressure per square inch neces-
sary to get up a given tensile force per square inch, we
multiply the given pull per square inch by the thickness
of the plate and divide by the radius in inches.
We can find the pressure per square inch necessary
to rupture the sheet by multiplying the ultimate tensile
strength, that is, the tensile force required to pull a
square inch of it apart by the thickness and dividing
by the radius.
Example. What pressure would be required to
burst a tank 48 inches in diameter, made of steel \
of an inch in thickness, having a uniform tensile
strength of 60,000 pounds per square inch?
Tensile strength X thickness
-^T. ' - = pressure,
radius
60,000 X .25 , .,
= 625 Ibs. per sq. in.
But we cannot or do not in boiler practice get a
shell of uniform strength. There have to be joints and
these joints are not so strong as the plate itself. We
will have a talk later about how to figure the strength
of a riveted joint. Suppose the riveted joint was only
70 per cent, of the plate strength, then it would take
only 70 per cent, of the force to pull it apart, and the
result just found must be multiplied by .70 if the tank,
instead of having a " uniform tensile strength of 60,000,"
has a sheet strength of 60,000 and a longitudinal seam
of 70 per cent, efficiency.
BURSTING STRENGTH OF BOILERS 29
The complete operation of finding the bursting
strength of a boiler shell is
Tensile strength X thickness X efficiency of joint
radius
RULE. Multiply the tensile strength of the weakest
sheet in pounds per square inch by the least thickness in
inches and by the efficiency of the longitudinal riveted
joint, and divide by the inside radius of the shell in
inches. The result is the pressure per square inch at
which the shell should split longitudinally.
The safe working pressure is found by dividing the
above by the desired ''factor of safety/' usually from
3-5 to 5.
This, it must be noted, is the pressure at which the
shell should fail in the manner described. The boiler
may be weaker somewhere else, as upon some of the
stayed surfaces, so that all these points should be con-
sidered before the allowable pressure is fixed upon.
SIMPLE TALKS ON THE BRACING OF
HORIZONTAL RETURN TUBULAR
BOILERS
IN former chapters we have discussed the strength
of a boiler so far as the parting of the shell is con-
cerned, but even if the shell is heavy enough and the
joint well proportioned the boiler may be weak in
other respects.
The head of a 6o-inch boiler has an area of
60 X 60 X 0.7854 = 2827 square inches.
At 100 pounds per square inch there would be a pres-
sure against the head of
2827 X 100 = 282700 pounds.
or over 140 tons.
Besides its tendency to pull the shell apart endwise,
this pressure tends to bulge the heads, as shown in
Fig. 22. In the case of a tank, or of the drums of
water-tube boilers where there are no tubes in the
heads, they can be made safe against change of shape
under pressure by giving them in the first place the
shape that the pressure tends to force them into; but
the tube sheet of a horizontal tubular boiler, for in-
3
HORIZONTAL RETURN TUBULAR BOILERS 31
stance, must be flat to allow the tubes to enter square
with its surface. The tubes themselves act as stays
to the lower part, but the pressure on the part above
the tubes tends to bulge the head and might cause
the central tubes to pull out.
FIG. 22.
This is prevented by bracing the unsupported part
of the head either by "through braces/' as in Fig. 23,
or by "diagonal braces/' as in Fig. 24.
In order to find how many braces are required, or if
a given boiler is sufficiently braced, the area to be
braced must be computed. This area may be taken
as that included within lines drawn 2 inches above
the top line of tubes and 2 inches inside of the shell,
3 2
BOILERS
HORIZONTAL RETURN TUBULAR BOILERS 33
34
BOILERS
as in Fig. 25, the area outside of these lines being con-
sidered to be sufficiently braced by the shell and tubes.
This figure is a "segment" of a circle and its area is
found by dividing its height h by the diameter of the
circle, of which it is a part, finding the quotient in the
column of " versed sines" of the accompanying table,
and multiplying the segmental area as given opposite
that quotient in the next column by the square of the
diameter.
oooooooooo
! O O O O O O O O O O O';
FIG. 25.
For example, suppose the hight b in Fig. 25 to be
1 8 inches and the diameter of the boiler 60 inches.
The diameter of the circle of which the segment is a
part is 56 inches, because we go 2 inches inside the shell
on both ends of the diameter.
Following the rule we divide the height by the
diameter
18 ~ 56 = 0.3214.
The values in the table are given to only three places
of decimals, but the division should be carried out to
HORIZONTAL RETURN TUBULAR BOILP:RS 35
four places. If the last figure is less than 5, drop it
off. If it is 5 and the quotient comes out even, i.e.,
there is no remainder after the 5, drop it off, also. If
the last figure is greater than 5, or in case it is 5, and
the division did not come out square, drop it off, but
raise the third figure one.
In the case in hand the quotient, 0.3214, conies be-
tween the 0.321 and 0.322 of the table, and is nearer
the 0.321, being but 0.3214 0.321 = 0.0004 ff
while it is 0.322 - 0.3214 = 0.0006 off from the
higher value. If it were 0.3216, however, it would be
nearer 0.322 than 0.321.
The segmental area corresponding with 0.321 in the
table is 0.2176. Multiplying this by the square of the
diameter gives 56 X 56 X 0.2176 = 682.39 square
inches as the area of the segment, and the force to be
braced against is this number of square inches mul-
tiplied by the pressure per square inch.
A through-brace which pulls squarely on the plate
has an effect in keeping it from bulging equal to the
tensile strain in the brace itself i.e., if the brace
were under a strain of 6000 pounds, it would tend to
pull the head in and keep it from bulging with an
equal force; but if a diagonal brace, as in Fig. 26, were
under a strain of 6000 pounds, it would tend to pull
the lug on the head in its own direction with that
force, but would resist a force in a direction at right
angles with the head of only .91 as much, or 5,460
pounds. This figure is found by dividing the length
of the line b c by the length of the line a b.
. In order to find if a boiler is sufficiently braced;
36 BOILERS
Find the smallest cross-section of each brace in
square inches.
Multiply the cross-section of each diagonal brace
by the quotient of the distance of its far end from the
head in a line perpendicular to the head (b c, Fig. 26),
divided by the length of the brace.
Add all these results together.
FIG. 26.
For such braces as are all alike, as for through-
braces of the same diameter of cross-section, you can
of course compute one and multiply it by the number
of similar ones.
Divide the product of the area to be braced and the
pressure per square inch by the sum of all these values,
and you will have the strain on the braces per square
inch of section.
The rules of the United States Board of Supervising
Inspectors allow a strain of 6000 pounds per square
inch on the braces. If the computed stress does not
exceed this amount, the boiler is sufficiently braced.
HORIZONTAL RETURN TUBULAR BOILERS
To determine what pressure a boiler will stand, so
far as its bracing is concerned, multiply the minimum
cross-section of each brace by the quotient of the dis-
tance of its far end from the plate perpendicularly di-
vided by the length of the brace. Add the results and
multiply by 6000. Divide the produce by the number
of square inches in the segment, and the quotient will
be the pressure per square inch that the bracing is good
for.
AREAS OF SEGMENTS OF CIRCLES
Versed
Sine.
Segmental
Area.
Versed
Sine.
Segmental
Area.
Versed
Sine.
Segmental
Area.
Versed
Sine.
Segmental
Area.
.1
.04087
.121
.05404
.142
.06892
.163
.08332
.101
.04148
.122
.05469
143
.06892
.164
.08406
.102
.04208
.123
05534
.144
.06962
.165
.0848
.103
.04269
.124
.056
145
07033
.166
08554
.104
.0431
125
.05666
.146
.07103
.167
.08629
.105
.04391
.126
05733
.147
.07174
.168
.08704
.106
.04452
.127
5799
.148
07245
.169
.08779
.107
.04514
.128
.05866
.149
.07316
.17
.08853
.108
4575
.129
05933
15
07387
.171
.08929
.109
.04638
13
.06
J 5i
07459
.172
.09004
.11
.047
131
.06067
.152
07531
173
.0908
.III
.04763
.132
06135
153
.07603
.174
09155
.112
.04826
133
.06203
i54
.07675
175
.09231
113
.04889
134
.06271
-155
.07747
.176
.09307
.114
4953
J 35
.06339
156
.0782
.177
.09384
US
.05016
.136
.06407
157
.07892
.178
.0946
.Il6
.0508
137
.06476
158
.07965
.179
09537
.117
.05145
.138
06545
159
.08038
.18
.09613
.118
.05209
i39
.06614
.16
.08111
.181
.0969
.119
.05274
.14
.06683
.161
.08185
.182
.09767
.12
.05338
.141
-06753
.162
.08258
.183
.09845
38 BOTLKRS
AREAS OF SEGMENTS OF CIRCLES Continued
Versed
Sine.
Segmental
Area.
Versed
Sine.
Segmental
Area.
Versed
Sine.
Segmental
Area.
Versed
Sine.
Segmental
Area.
.184
.09922
.216
.12481
.248
.15182
.28
.18002
185
.1
.217
.12563
.249
.15268
.281
.18092
.186
.10077
.218
.12646
25
.15355
.282
.18182
.187
IOI55
.219
.12728
.251
.15441
.283
.18272
.188
.10233
.22
.12811
252
.15528
.284
.18361
.189
.10312
.221
.12894
253
15615
.285
.18452
.19
.1039
.222
.12977
254
.15702
.286
.18542
.191
.10468
.223
.1306
255
15789
.287
18633
.192
.10547
.224
.i3 J 44
.256
.15876
.288
.18723
193
.10626
.225
.13227
257
.15964
.289
.18814
.194
.10705
.226
I 33n
258
.16051
.29
.18905
195
.10784
.227
J 3394
259
.16139
.291
.18995
.196
.10864
.228
.13478
.26
.16226
.292
.19086
.197
.10943
.229
.13562
.261
.16314
293
.19177
.198
.11023
23
.13646
.262
.16402
294
.19268
.199
.IIIO2
.231
I373I
.263
.1649
.295
.1936
.2
.IIl82
.232
13815
.264
.16578
.296
I945r
.201
.11262
2 33
.139
265
.16666
297
.19542
.202
II343
234
.13984
.266
.16755
.298
19634
.203
.11423
235
.14069
.267
.16844
299
19725
.204
.H503
.236
I4I54
.268
.16931
3 '
.19817
.205
.11584
.237
.14239
.269
.1702
.301
.19908
.206
.11665
.238
.14324
27
.17109
.302
.2
.207
.11746
239
.14409
.271
.17197
303
.20092
.208
.11827
.24
.14494
.272
.17287
304
.20184
,2O9
.11908
.241
.1458
273
.17376
305
.20276
.21
.1199
.242
.14665
.274
.17465
.306
.20368
.211
.12071
243
i475i
275
17554
307
.2046
212
I2I53
244
14837
.276
.17643
308
20553
2I 3
12235
245
.14923
.277
17733
309
.20645
.214
.12317
.246
. 1 5009
.2 7 8
.17822
3i
.20738
.215
.12399
.247
.i5 95
279
.17912
311
2083
HORIZONTAL RETURN TUBULAR BOILERS 39
AREAS OF SEGMENTS OF CIRCLES- Continued
Versed
Sine.
Segmental
Area.
Versed
Sine.
Segmental
Area.
Versed
Sine.
Segmental
Area.
Versed
Sine.
Segmental
Area.
.312
.20923
343
23832
374
.26804
405
.29827
.313
.21015
344
.23927
375
.26901
.406
.29925
.314
.21108
345
.24022
376
.26998
.407
.30024
315
.21201
346
.24117
377
.27095
.408
.30122
.316
.21294
347
.24212
378
.27192
.409
.3022
3*7
.2I38 7
348
.24307
379
.27289
.41
30319
.318
.2148
349
.24403
38
.27386
.411
30417
3i9
21573
35
.24498
.381
27483
.412
30515
.32
.21667
351
24593
382
.27580
413
.30614
.321
.2176
352
.24689
383
.27677
.414
.30712
.322
21853
353
.24784
384
27775
.415
.30811
323
.21947
354
.2488
385
.27872
.416
30909
3 2 4
.22O4
355
.24976
386
.27969
.417
.31008
325
.22134
356
.25071
387
.28067
.418
.31107
.326
.22228
357
.25167
388
.28164
.419
31205
327
.22321
358
25263
389
.28262
.42
31304
.328
22415
359
25359
39
28359
.421
31403
329
.22509
36
25455
391
.28457
.422
31502
33
.22603
361
25551
392
28554
423
.316
331
.22697
.362
.25647
393
.28652
.424
.31699
332
.22791
363
25743
394
.2875
.425
31798
333
.22886
364
25839
395
.28848
.426
-3 l8 97
334
.2298
365
2593 6
.396
28945
.427
.31996
335
.23074
.366
.26032
397
.29043
.428
32095
336
.23169
367
.26128
.398
.29141
.429
.32194
337
.23263
.368
.26225
399
.29239
43
.32293
338
.23358
369
.26321
4
2 9337
431
32391
339
23453
37
.26418
.401
29435
432
3249
34
23547
371
26514
.402
29533
433
3259
341
.23642
372
.26611
.403
.29631
434
.32689
342
2 3737
373
.26708
.404
.29729
435
32788
VI
CALCULATING THE STRENGTH OF
RIVETED JOINTS 1
IN calculations relative to the strength of steam
boilers and vessels of a similar character for withstand-
ing high pressures, one of the most important points
to be considered is the strength of the seams where the
plates are joined. This is not only important to the
designer of such vessels, but also to the operating
engineer, who is often required to fix the limit of pres-
sure which should be carried on the boilers under his
charge, and frequently, owing to increased output
without corresponding addition to the boiler capacity,
it becomes necessary to carry the pressure as high as
safety will permit, and in such cases it is important for
the engineer to be able to fix this safe limit.'
It is the purpose in this chapter to show how the
strength of the various types of joint generally used in
boiler construction may be calculated, and as only
simple arithmetic is required for the calculations, any
reader should find no difficulty in understanding how
it is done, and applying the principles to calculate
the strength of the particular joints which may be of
interest to them. To avoid the use of formulas, which
1 Contributed to Power by S. F. Jeter.
40
STRENGTH OF RIVETED JOINTS 41
are confusing to many, numerical examples will be
used to illustrate the methods of making the calcula-
tions, and for the sake of uniformity the tensile strength
of the sheets (which is the strength to resist being
pulled apart) will be assumed as 55,000 pounds per
square inch; the shearing strength of the rivets (which
represents their resistance to being sheared through
by the plates at right angles to their length) will be
assumed as 42,000 pounds per square inch in single
shear, as represented in Fig. 31, and 78,000 pounds
per square inch in double shear, as represented in Fig.
34. The resistance of the rivets to crushing will be
assumed at 95,000 pounds per square inch. For
modern construction consisting of steel plates and steel
rivets, the above values are average figures.
It is customary to express the strength of a riveted
joint as a percentage of the strength of the plates which
are riveted together. Thus, if the joint illustrated in
Fig. 35 has an efficiency of 62^ per cent., it would mean
that any portion of its length that divides the rivet
spaces symmetrically would be 0.625 times as strong
as a section of the same length through the solid plate.
POSSIBLE MODES OF FAILURE
Before proceeding to calculate a practical boiler
joint, the different ways in which two pieces of plate
riveted together might fail should be noted. If a piece
of boiler plate, f inch thick and 2| inches wide, is placed
in the jaws of a testing machine, as illustrated in Fig. 27,
and pulled apart, it would separate at some section as
A A. If the tensile strength was 55,000 pounds per
42 BOILERS
square inch, the force that would have to be applied
to the jaws would be 55,000 times the area separated
in square inches, which in this case is
2! X f = H = -9375
square inch, so that the pull would be
pounds. 55-000X0.9375 = 5, ,562.5
If another piece of plate be taken, identical in every
rf--j \
/ - ; !l
/
SK
V' 1 (
i B fl- B -
r i S
\ \ !i r
-\ r
\
hi: (
j i~J L
J
~H u
P
FIG. 27.
M
FIG. 28.
respect to the first, except that a hole i inch in diameter
is drilled through it as illustrated in Fig. 28, and the
plate be pulled apart in the testing machine as before,
it is evident that it would fail along the line B B, as
the area of the reduced section caused by drilling the
hole would be only
(2.5 i) X 0.375 = 0.5625
square inch, and the force necessary to pull it apart
would be
55,000 X 0.5625 = 30,937.5
STRENGTH OF RIVETED JOINTS
43
pounds, the strength of the metal being the same in
both instances. Now if the relation between the
strength of the solid plate and the drilled plate be
expressed by dividing the latter by the former, the
result would be ^^ ^
51,562.5
or, in other words, the drilled plate is capable of sus-
taining 60 per cent, of the load that could be carried
by the solid plate.
If, instead of using a single piece of plate, two plates
are drilled with i-inch holes in the ends and are joined
together by a rivet, as shown in Fig. 29, and an attempt
FIG. 30.
should be made to pull them apart as before, there
would be four probable ways in which failure might
take place, all of which are considered in the calculation
and design of riveted joints. First, the section of plate
each side of the rivet hole might break, leaving the ends
44
BOILERS
as shown in Fig. 30. Again, the plates might shear the
rivets off, as illustrated in Fig. 31. Thirdly, it has been
found by practical tests of joints that steel rivets can-
not be subjected to a pressure much greater than
95,000 pounds per square inch of bearing surface
without materially affecting their power to resist
shearing, and therefore the joint might fail, as shown
in Fig. 31, due to an excess crushing stress on the rivet.
QD
oh
FIG. 31.
FIG. 32.
A fourth possible method of failure would be for the
metal in the sheet in front of the rivet to split apart
or pull out, as illustrated in Fig. 32. This latter mode
of failure is erratic, and cannot be calculated, but it
has been practically demonstrated in tests of joints,
that if the distance from the edge of the plate to the
center of the rivet hole is i \ times the diameter of the
hole, this mode of failure is improbable, and in the fol-
lowing calculations of joints it will be assumed that
they are properly designed to render such failure im-
possible.
STRENGTH OF RIVETED JOINTS 45
To determine the actual strength or efficiency of
such a joint as is illustrated in Fig. 29, the force re-
quired to produce rupture must be calculated for each
of the first three ways mentioned, and the weakest
mode of failure taken as the maximum strength of the
joint.
To rupture the plate as illustrated in Fig. 30, the
pull required would be the same as to rupture the
drilled plate illustrated in Fig. 28, which was found
to be 30,937.5 pounds. To shear the rivet off, as in Fig.
31, would require a force equal to the area to be sheared
in square inches, times the shearing strength per square
inch; or since the area of a i-inch rivet is 0.7854 square
inch, the force required would be
0.7854 X 42,000 = 32,987
pounds. The pressure required to cause failure by
crushing was stated to be 95,000 pounds per square
inch, and in calculating the area exposed to pressure
for pins and rivets, it is figured as equal to the diameter
of the pin or rivet, times the thickness of the plate;
therefore, we have
i X 0.375 = o-375
square inch of area to withstand crushing, or
0.375 X 95,000 - 35,625
pounds would be required to produce rupture of the
joint in this manner.
From these figures it is evident that the method
of failure first considered is the weakest of the three,
BOILERS
and, therefore, determines the efficiency of the joint,
which would be 60 per cent, as found for the drilled
plate.
If one plate is riveted between two other plates, as
illustrated in Fig. 33, the several methods of failure
are calculated in the same way, except for the shearing
of the rivet, which would occur as shown in Fig. 34, and
61261 Lbs.
FIG. 33.
FIG. 34.
is described as double shearing. While the metal
sheared in this case would be just twice as much as in
single shear, it has been found by test that the force
required is not exactly twice as much, but 1.85 to 1.90
times the amount in single shear; so as stated at the
beginning, 78,000 pounds per square inch is .assumed
for rivets in double shear and 42,000 pounds per square
inch when in single shear.
Calculating the strength of a joint with the dimen-
sions as illustrated in Fig. 34, the strength of the solid
plate would be
3 X 0.75 X 55,000 = 123,750
pounds, The strength of the center plate through the
STRENGTH OF RIVETED JOINTS 47
rivet hole, the failure being assumed similar to that
illustrated in Fig. 30, would be
(3 - i) X 0.75 X 55,000 = 82,500
pounds. The crushing strength of the rivet would be
i X 0.75 X 95,000 - 71,250
pounds. The shearing strength of the rivet, or failure
assumed as in Fig. 34, would be
0.78154 X 78,000 = 61,261
pounds.
From these figures it is evident that failure would
most likely occur as shown in Fig. 34, and the relative
strength of the joint as compared with the solid plate is
61,261
- = 0.495,
123,750
or 49 J per cent. As will be shown later, the foregoing
simple calculations are all that are required to estimate
the strength of the most complicated joints.
THE UNIT SECTION
In calculating the strength of a practical boiler
joint, the strength for the entire length of a sheet could
be estimated, but this would be laborious owing to the
number of figures involved in the calculations, and the
same result can be obtained by considering any length
that divides the rivets symmetrically. For convenience,
the shortest length that thus divides the rivets is the
one used in such calculations, and this length is called
a unit section of the joint. When the lines dividing the
48 BOILERS
joint into unit sections pass through a rivet, only one-
half of the rivet is considered in the calculation, and
when rivets thus divided are lettered for reference, the
two halves on opposite sides will be lettered the same,
so that referring to the letter will indicate a whole rivet.
Thus, if the rivet A, in Fig. 43, is spoken of, it would
mean the combined halves of the two rivets on the
outer row.
In measuring joints already constructed to obtain
the length of a unit section, or the pitch, it should be
remembered that rivet heads do not always drive fairly
over the center of the rivet holes, and the rivet holes
themselves are sometimes irregular distances apart;
so it is more accurate to measure a number of pitches
and divide the distance by the number measured to
obtain the average pitch. It will be found most con-
venient, where space permits, to measure ten pitches,
and then placing the decimal point one figure to the left
will give the average unit length.
SINGLE-RIVETED LAP-JOINT
First to be considered is the single-riveted lap-joint
illustrated in Fig. 35. In a unit section of 2 inches
one rivet is in single shear and J inch has been cut out
of the plate by the rivet hole. The calculation for
strength is the same as has been made for Fig. 38, and
the three methods of failure to be considered are:
(1) Breaking of the section of plate between the
rivet holes, which is called the net section.
(2) Shearing of a f-inch rivet in single shear.
(3) Resistance of one rivet to crushing.
STRENGTH OF RIVETED JOINTS
49
Using the numerical values given in Fig. 35 the
following results are obtained:
(1) (2 - 0.75) X 0.25 X 55,000 = 17,187.5 pounds.
(2) 0.4418 X 42,000 = 18,556 pounds.
(3) 0.75 X 0.25 X 95,000 - 17,812.5 pounds.
-
rfDU-HoU^ |^l
6<
^CJ)@(pi
c
L
4x
FIG. 35.
Of the three methods of failure, the first is seen to
be the most probable, and since a unit section length
of the solid plate would have a strength of
2 X 0.25 X 55,000 = 27,500
pounds, the efficiency of the joint would be
17,187.5
= 62.5
27,500
per cent.
DOUBLE-RIVETED LAP-JOINT
Next in line is the double-riveted lap-joint illustrated
in Fig. 36. There is one feature connected with this
joint which should be considered before proceeding
with the calculation of its strength. It would evi-
dently be possible to have the two rows of rivets form-
ing this joint so close together that the combined net
50 BOILERS
sections between rivets A B and B C would be less
than between rivets AC. It has been found in prac-
tical tests of joints that it is necessary to have the com-
bined area of these two sections 30 to 35 per cent, in
excess of that between rivets A and C in order to be
sure that the joint will fail along line A C. This would
FIG. 36.
correspond to a diagonal pitch of two-thirds of the
pitch from A to C plus one-third of the diameter of
the rivet hole, or 1.9 inches in the joint shown in Fig.
36. Ordinarily, if the rows are much closer than this,
the joint has an abnormal appearance which would
be noted at once. In further calculations it will be
assumed that the joints are proportioned so that this
method of failure will not be possible.
Proceeding with the calculation of the strength of
the joint illustrated in Fig. 36, the methods of probable
failure to be calculated are the same as for the single-
riveted joint:
(1) Failure of net section between rivet holes.
(2) Shearing of two rivets in single shear.
(3) Crushing strain on two rivets.
STRENGTH OF RIVETED JOINTS 51
Using the values given in Fig. 36, we have for the
above :
(1) (2.5 - 0.75) X 0.3125 X 55,000 = 30,078
pounds.
(2) 2 X 0.4418 X 42,000 = 37,112 pounds.
(3) 2 X 0.75 X 3.5120 X 95,000 = 44>53 I pounds.
It is evident that the first method of failure is the
most probable, and since the strength of the solid
P at< 2.5 X 0.3125 X 55,000 = 42,969
pounds, the efficiency of the joint will be
30,078
7-= 70
42,969
per cent.
TRIPLE-RIVETED LAP-JOINT
In Fig. 37 is illustrated a triple-riveted lap-joint.
Here the length of unit section is 3 inches, and the
different probable modes of failure are identical with
those of the single- and double-riveted lap-joints
except in rivet strength. It will be noted that in this
case there are three rivets contained in each unit
section, which are subjected to shear and crushing.
The several methods of probable failure to be inves-
tigated are as follows:
(1) Failure of net section between the rivet holes
of outer rows.
(2) Shearing of three rivets in single shear.
(3) Crushing strain on three rivets.
52 BOILERS
Using the numerical values specified in Fig. 37, we
Would have:
(1) (3 0.75) X 0.375 X 55,000 = 46,406 pounds.
(2) 3 X 0.4418 X 42,000 = 55,667 pounds.
(3) 3 X 0.75 X 0.375 X 95,000 = 80,156 pounds.
JiDia. Hole
FIG. 37.
The first method of failure assumed is the most
likely, and as the strength of the solid plate for a unit
section of length is
3 X 0.375 X 55,000 = 61,875
pounds, the efficiency of joint is
46406 _
6i,8 75 ~ 75
per cent. The triple-riveted joint represents about
the maximum strength that can be obtained in prac-
tice from simple lap-riveted joints, as in this form the
maximum pitch distance that permits proper calking
of the edge of the plates is reached, and still leaving
STRENGTH OF RIVETED JOINTS
53
the net section of metal between the rivet holes the
weakest portion of the joint, so that further addition
of rivets would not add to its strength.
CHAIN RIVETING
Joints illustrated in Figs. 36 and 37 have the rivets
arranged so that the rivets in one row come opposite the
FTG. 39.
spaces in the adjacent rows, and this arrangement is
termed staggered riveting. The same forms of joint are
sometimes made with the rivets placed in straight rows
across the joint, is illustrated in Figs. 38 and 39, which
is known as chain riveting. The calculations for joint
54
BOILERS
efficiency in chain-riveted joints are identical in every
respect to those for staggered riveting, and with equal
diameters and spacing of rivets and equal thicknesses
of plate, the efficiencies are the same for either type.
LAP-RIVETED JOINT WITH INSIDE STRAP
While the lap-riveted joint with inside strap is not
extensively used in the manufacture of new boilers, it
affords a ready means of strengthening simple lap
FIG. 41.
seams on boilers already constructed, and it is quite
extensively used for this purpose. This joint is
illustrated in Figs. 40 and 41, and it will be seen that
it is equally applicable to single- or double-riveted
STRENGTH OF RIVETED JOINTS 55
lap-joints; it could also be applied to triple-riveted
joints. The joint illustrated in Fig. 40 is identical in
every respect with the one shown in Fig. 36, excepting
the addition of the fVmch cover strip and the outer
rows of rivets, these dimensions being selected to facili-
tate comparison between the strengths of the two
joints. A unit section of this joint is 5 inches long,
and five methods of failure present themselves for
consideration in determining the strength of the joint:
(1) Breaking of the plate along the section between
the rivet holes A A.
(2) The separation of the plate along the section
on line of rivets CD and shearing the rivet A.
(3) Separation of the plate along the section on
line of rivets C D and the crushing of rivet A.
(4) Crushing of rivets A B C D E by the shell.
(5) Shearing of rivets B CD E F in single shear.
The pulling out of the upper plate, which would
shear rivet A single, and E CD E double, need not be
considered, since it would evidently be stronger than
the first method considered above. Calculating the
value of the possible methods of failure by using the
dimensions given in Fig. 40, we have:
(1) (5 - 0.75) X 0.3125 X 55,000 = 73,040 pounds.
(2) [5 - (2 X 0.75)] X 0.3125 X 55,000 + 0.4418
X 42,000 = 78,726 pounds.
(3) [5 " (2 X 0.75)] X 0.3125 X 55,000 + 0.3125
X 0.75 X 95,000 = 82,436 pounds.
(4) 0.3125 X 0.75 X 95,000 X 5 = ii 1,330 pounds.
(5) 0.4418 X 42,000 X 5 = 92,780 pounds.
56 BOILERS
Evidently the next section between the rivet holes
A A is the weakest portion of the joint, and since a
section of the solid plate 5 inches long has a strength of
5 X 0.3 125 X 55,000 = 85,937
pounds, the efficiency of the joint is
S^o _ 8
percent. 8 5'937
Calculation of the joint illustrated in Fig. 41 is pro-
ceeded with in the same manner as for Fig. 40. It will be
noted that to aid comparison the dimensions have been
assumed the same as in Fig. 35 with the strap added.
The methods of possible failure to be compared are:
(1) Separation of the plate along net section G G.
(2) Separation of plate along section H I and shear-
ing of rivet G in single shear.
(3) Separation of plate along section H I and crush-
ing of rivet G.
(4) Crushing of rivets G H I.
(5) Shearing of rivets H I J in single shear.
According to the dimensions given in Fig. 41 the
numerical values would give the following results.
(1) (4 - 0.75) X 0.25 X 55,000 = 44,687 pounds.
(2) [4 - (2 X 0.75)] X 0.25 X 55,000 + 0.4418 X
42,000 = 52,931 pounds.
(3) [4 - (2 X 0.75 )]X 0.25 X 55,000 + 0.75 X
0.25 X 95,000 = 51,187 pounds.
(4) 0.75 X 0.25 X 95,000 X 3 == 53,436 pounds.
(5) 0.4418 X 42,000 X 3 = 55,668 pounds.
STRENGTH OF RIVETED JOINTS
Since the strength of the solid plate is
4 X 0.25 X 55,000 = 55,000
pounds, the efficiency would be
= 81.25
57
5 5 ,OOO
per cent.
It is thus apparent that by adding a strap to the
joint illustrated in Fig. 35 and making it like Fig. 41,
the efficiency has been increased from 62.5 per cent, to
81.25 P er cent., which would permit an increase in steam
pressure of 30 per cent, on the boiler after such change.
SINGLE-RIVETED DOUBLE-STRAPPED BUTT-JOINT
In describing all forms of butt-joints it is customary
to refer to the rivets on one side of the butt only; thus,
in Fig. 42 there are actually two rows of rivets, but
FIG. 42.
the joint is only single-riveted, for the strength of the
joint along either row is in no wise dependent on the
other row. If the two rows should not be riveted alike,
it would be necessary to consider each side as a separate
joint to find which was the weaker, in order to deter-
58 BOILERS
mine the strength of the combination. This, how-
ever, is not necessary in practical boiler joints, since
they are constructed alike on each side of the butt.
In the joint illustrated in Fig. 42 it will be noted that
all of the rivets are in double shear, and only three
methods of possible failure are presented for calcula-
tion:
(1) Breaking the net section.
(2) Shearing of one rivet in double shear.
(3) Crushing of a rivet by the shell.
With the dimensions given in the figure we have:
(1) (2.25 -- 0.75) X 0.3125 X 55,000 == 25,781
pounds.
(2) 0.4418 X 78,000 = 34,460 pounds.
(3) 0.75 X 0.3125 X 95,000 = 22,230 pounds.
The strength of the solid plate is
2.25 X 0.3125 X 55,000 = 38,672
pounds, and since the weakest portion of the joint is
the resistance to crushing of the rivets, the efficiency is
22,230 _
38,672 ~ 57 ' 5
per cent.
DOUBLE-RIVETED DOUBLE-STRAPPED BUTT-JOINT
Double-riveted butt-joints can be made in two forms,
the one generally used being illustrated in Fig. 43.
The calculations for the efficiency of this joint are the
same as for the single-riveted joint, except that there
STRENGTH OF RIVETED JOINTS
59
are two rivets to be considered in each unit section
of the joint instead of one. The three methods of pos-
sible failure are :
(1) Pulling apart of the sheet along net section A A.
(2) Shearing of rivets, A B, in double shear.
(3) Crushing of rivets A B.
r
.
i %$ , B ,
\ w---7s-r A A
FIG. 43.
Substituting the values given in Fig. 17, we have:
(1) (2.5 - 0.75) X 0.3125 X 55,000 = 29,085
pounds.
(2) 0.4418 X 78,000 X 2 = 68,920 pounds.
(3) 0.75 X 0.3125 X 95,000 X 2 = 44,532 pounds.
The strength of the solid plate is
2.5 X 0.3125 X 55,000 = 42,969
pounds, and the weakest portion of the joint is the net
section between rivets A A. Therefore, the efficiency is
per cent.
42,969
= 6 7 .6
6o
BOILERS
In Fig. 44 is illustrated the second type of double-
riveted butt-joint. This form of joint, if proportioned
properly, can be made considerably stronger than the
one illustrated in Fig. 43. There are six methods of
possible failure to be considered:
FIG. 44.
(1) Pulling apart of the sheet along net section A A.
(2) Pulling apart of the sheet along section B C and
shearing rivet A.
(3) Pulling apart of sheet along section- B C and
crushing of rivet A. (Note that in calculating the
crushing of rivet A the thickness of the strap is to be
used instead of the plate, owing to the strap being
thinner than the plate.)
(4) Shearing of rivet ^single and B, C double shear.
(5) Crushing of rivets B C in the plate and A in
the strap.
(6) Crushing of rivets B C in the plate and shear-
ing of rivet A.
STRENGTH OF RIVETED JOINTS 61
Substituting the numerical values from Fig. 44, we
have:
(1) (4 - 0.75) X 0.3125 X 55,000 = 55,859 pounds.
(2) [(4 - 1.5) X 0.3125 X 55,000] + (42,000 X
0.4418) - 61,525 pounds.
(3) [(4 - 1.5) X 0.3125 X 55,000] + (0.75 X 0.25
X 95,000) == 60,781 pounds.
(4) (42,000 X 0.4418) -f (78,000 X 0.4418 X 2) =
87,476 pounds.
(5) (o./5 X 0.3125 X 95,000 X 2) + (0.75 X 0.25
X 95,000, = 62,272 pounds.
(6) (0.75 X 0.3125 X 95,000 X 2) + (42,000 X
0.4418) == 63,087.25 pounds.
From these figures it will be seen that the net sec-
tion between the rivet holes A A is the one most
likely to fail, and since the strength of a unit section
of the solid plate is
4 X 0.3125 X 55.000 = 68,750
ponuds, the efficiency of the joint is
- 81.25
per cent. 68 >75O
TRIPLE-RIVETED DOUBLE-STRAPPED BUTT-JOINT
The joint illustrated in Fig. 45 is known as the
triple-riveted butt-joint. The methods of failure to
be investigated are the same as those in Fig. 44, and
are as follows :
(i) Pulling apart of sheet at net section A A.
62
BOILERS
STRENGTH OF RIVETED JOINTS 63
(2) Pulling apart of sheet along section C E and
shearing rivet A.
(3) Pulling apart of sheet along section C E and
crushing rivet A.
(4) Shearing rivet A single and B C D E double.
(5) Crushing of rivets B C D E in the plate and A
in the strap.
(6) Crushing of rivets B C D E in the plate and
shearing of rivet A.
Substituting the values given in Fig. 45 :
(1) (7.5 -- i) X 0.5 X 55,000 == 178,750 pounds.
(2) [(7.5 - 2) X 0.5 X 55,000] + (42,000 X 0.7854)
= 184,237 pounds.
(3) [(7-5 -- 2) X 0.5 X 55>o] + X 0.5 X
95,000) = 198,250 pounds.
(4) (0.7854 X 42,000) + (0.7854 X 78,000 X 4) =
278,027 pounds.
(5) (i X 0.5 X 95,000 X 4) + X 0.375 X 95,000)
= 225,625 pounds.
(6) (i X 0.5 X 95,000 X 4) + (0.7854 X 42,000)
= 222,987 pounds.
For a unit length the strength of the solid plate is
7.5 X 0.5 X 55,000 = 206,250
pounds. The net section between rivets A, A is the
weakest portion of the joint, so that the efficiency is
per cent.
_ 86 . 7
206,250
64 BOILERS
QUADRUPLE-RIVETED DOUBLE-STRAPPED BUTT-JOINT
The last type of joint to be considered is the quad-
ruple-riveted butt-joint illustrated in Fig. 46. This
joint is now used on nearly all high-grade boilers of
the horizontal return-tubular type, and it marks
about the practical limit of efficiency for riveted joints
connecting plates of uniform thickness together.
The methods of failure to be considered are practically
the same as in the two preceding joints, except that
there are more rivets concerned in the calculations:
(1) Pulling apart of the sheets along net section
A A.
(2) Pulling apart of the sheet along section D E F G
and shearing rivets ABC.
(3) Pulling apart of sheet along section D E F G
and crushing of rivets A B C in the strap.
(4) Shearing rivets A B C in single shear and D
E F G H I J K in double shear.
(5) Crushing of rivets D E F G H I J K in plate and
A B C in the strap.
(6) Crushing of rivets D E F G H I J K in 'the plate
and shearing rivets ABC.
Using the numerical values of Fig. 46, we have:
(1) (15.5- i) X 0.5625 X 5 5, ooo = 448, 580 pounds.
(2) [(15.5 - 4) X 0.5625 X 55,000] + (3 X 42,000
X 0.7854) = 454,739 pounds.
(3) [(15.5 - 4) X 0.5625 X 55>] + (3 X 0.4375
X i X 95,000) = 480,465 pounds.
F X RIVETED JOINTS
OF THS
UNIVERS
66 BOILERS
(4) (3 X 42,000 X 0.7854 ) + (8 X 78,000 X 0.7854)
= 589,050 pounds.
(5) (8 X 0.5625 X i X 95,000) + (3 X 0.4375 X
I X 95,000) == 552,187 pounds.
(6) (8 X 0.5625 X i X 95,000) + (3 X 42,000 X
0.7854 = 526,461 pounds.
The strength of the solid plate is
15.5 X 0.5625 X 55,000 = 479,528
pounds, and the failure of the sheet by pulling apart
along the net section A A is the one that determines
the efficiency of the joint, which is
448.580^
per cent. 479.528
From the foregoing calculations it may be observed
that estimating the efficiency of riveted joints, while
very simple, is a rather tedious process, particularly
if many joints are to be calculated
VII
TO FIND THE AREA TO BE BRACED IN THE
HEADS OF HORIZONTAL TUBULAR
BOILERS
FOR the purpose of determining the number of braces
to be used, it is not necessary to figure the area of a
boiler head to a fraction of a square inch, and a simple
rule, the reason for which is so plain that it can never
be forgotten, will be helpful to the candidate before
the examiner, or when a table of circular segments is
not to be had.
The diameter of the boiler and the hight above the
top row of tubes are the only measurements which are
ordinarily given. The flange is considered good for
three inches around the outside, and the tubes for two
inches above their top edges, so that the area to be
braced is a part of a circle having a diameter six inches
less than the given diameter of the boiler and a hight
5 inches less than that of the undiminished segment,
which area is represented by the shaded area in Fig. 47.
The area of a circle is the diameter multiplied by
itself and by 0.7854. It is easy, then, to find the area
of the circle of which the shaded area is a part. Sup-
pose We are dealing with a 72-inch boiler. Allowing
for 3 inches on each end of the diameter, the diameter
67
68 BOILERS
of the circle of which the segment to be braced is a part
would be rr . ,
72 6 = 66 inches,
and its area would be
66 X 66 X 0.7854 = 3421 square inches;
and the area of the half circle abode would be one-
half of this, or 1710 square inches.
FIG. 47.
Now, if from this area the area a b d e is subtracted,
the remainder will be the required area of the (shaded)
portion to be braced. The hight / g is the radius, or
one-half the given diameter less the given hight plus 2,
and it will be near enough if we consider its length
equal to the diameter, as the length of the chord b d is
not usually given. Suppose the hight h i to be 26 inches,
then the hight / g of the portion to be subtracted would
be
- 26 + 2 = inches,
HORIZONTAL TUBLAR BOILERS 69
and if its length be taken at 66 inches its area will be
12 X 66 = 792 square inches.
This is too great by the area of the two little dotted
triangles at a b and d e, but this is so small a proportion
of the total area that it may be neglected, especially if
it is borne in mind when deciding upon the number of
braces that the area as determined is a little small.
Subtracting this area from that of one-half the 66-
irich circle, as above found, we have
1710 792 =918 square inches
as the area to be braced.
If the pressure is 100 pounds per square inch, the
force to be braced against is
918 X 100 = 91,800 pounds,
and if the braces used are good for 8000 pounds apiece,
it will take
91,800 ~ 8000 =11.5 braces.
We should have to use 12 braces, anyway, and these
would be good for
12 X 8000 , . ,
- = 960 inches,
100
while the actual area is 936, instead of 918, as the above
approximate method made it. Unless the number of
braces comes out very nearly square in the calcula-
tion, there will be enough leeway in using a whole
brace for the fraction to make up for the shortness
of the area. When this fraction exceeds, say, 0.9,
safety would be insured by putting in an extra brace.
VIII
GRAPHICAL DETERMINATION OF BOILER
DIMENSIONS *
THE variables entering into the design of a steam
boiler shell are the working pressure, the diameter
of the shell, the thickness and tensile strength of the
plate, the diameter, spacing and shearing value of the
rivets, the efficiency of the joints and the factor of
safety.
The usual working pressures are 80, 100, 125, and
150 pounds per square inch.
The standard diameters of shell are 44, 48, 54, 60,
66, 72, 78, 84, 90 and 96 inches.
The tensile strength of the plate is 52,000 to 62,000
pounds per square inch for flange steel and 55,000 to
65,000 pounds per square inch for fire-box steel. The
average assumed for calculations is 60,000 pounds per
square inch. The shearing value of steel rivets is
38,000 to 42,000 pounds per square inch. Until
recently 38,000 pounds per square inch was used for
all calculations, but this value has been gradually
increasing with the improved quality of steel rivets,
until 42,000 pounds per square inch is now the more
generally accepted value.
1 Contributed to Power by N. A. Carle.
70
BOILER DIMENSIONS 71
This has resulted in an increased spacing of rivets,
together with an increase in the efficiency of the joints,
and a consequent reduction in the thickness of plate.
Rivet holes are usually punched T V-inch larger than
the rivets and calculated as J-inch larger than the
rivets.
In marine practice, holes are specified as drilled or
punched T V~inch small, the shell assembled and the
holes then reamed to full size.
The shearing value of the rivet is calculated for the
stock size before driving.
The crushing value of steel rivets has been practi-
cally eliminated from the problem, because in practice
the sizes selected give values in excess of the shearing
value.
No consideration is given to the friction of the joint,
it being assumed that this is all destroyed before rup-
ture, so that it is not a factor of the ultimate strength.
The kind of joints and size and spacing of the rivets
are governed by accident insurance companies' re-
quirements and shop practice.
The size of rivets and spacing used necessary to
insure good calking usually make the horizontal joint
the weakest point in the boiler and therefore the
governing factor.
It is desirable to get a high efficiency of the joint for
high pressures and thick plates. Different types of
joints are designated as single lap-riveted, double
lap-riveted, triple lap-riveted, double butt-strap-
riveted, triple butt-strap-riveted and quadruple butt-
strap-riveted.
72 BOILERS
The single lap-riveted joint is used on girth seams
generally, as the stress is only one-half that on the
horizontal joint, and on the horizontal seams only
for very small diameters and pressures.
The quadruple butt-strap-riveted joint is used only
on very heavy plate, large diameters and high pres-
sures.
The efficiencies depend upon the rivet spacing,
diameter of rivets and the allowances and assumptions
made.
Design conditions reduce the problem to the effi-
ciency of the joint based on tearing between the outer
row of rivets.
The usual efficiencies used in calculations in the
shell formula are double lap, 70 per cent.; triple lap,
75 per cent.; double butt-strap, 80 per cent., and triple
butt-strap, 86 per cent.
The factors of safety ordinarily used are 4, 4! and 5,
with 6 sometimes specified in marine practice.
The shell formula is
D. X W. P. X F. S. = 2 X 5. X E. X *.
D. = Diameter of shell in inches.
W . P. == Working pressure in pounds per square inch.
F. S. = Factor of safety.
E. = Efficiency of horizontal joint.
/. = Thickness of plate in inches.
These are shown graphically in the calculating
diagram (Fig. 48). The use of this diagram is probably
best illustrated by an example:
Given. The boiler shell 66 inches in diameter
BOILER DIMENSIONS
73
for a working pressure of 125 pounds with a factor of
safety of 5. What thickness of plate is required for
the shell?
Assume that a double butt-strap joint will be used
with an efficiency of 80 per cent. Starting with 66
inches "diameter of shell," read across to 125 pounds
74 BOILERS
"working pressure/' then up to a "factor of safety"
of 5, and then across to its intersection with a vertical
line through 80 per cent, "efficiency of joint." This
gives a value slightly less than T 7 ^ inch for "thickness
of plate."
Hence use T 7 e inch and by reading back it will be
found that this gives about 5.1 as factor of safety.
Usually the designer has shop practice to follow,
so that instead of using approximate values for the
efficiency, the usual spacing and diameter of rivets can
be selected and the actual efficiency obtained. As an
example, assume that for a double butt-strap-riveted
joint the shop spacing was 4J inches and 2\ inches,
using ^-inch rivets. Read across from 4^ inches
"spacing of rivets" to ^-inch rivets and then up to
82 per- cent, "efficiency of horizontal joint." The
boiler heads are made T V inch thicker than the shell,
as the metal is decreased about this amount in dishing
and flanging the head. The spacing of the girth-
seam rivets is according to shop practice and does not
require a high efficiency, as the stress is only one-
half that of the shell. It is, therefore, a dependent
factor in the design.
IX
THE SAFETY VALVE
THE study of the safety valve has been the first step
of many a man in scientific engineering. Induced to
its study by the necessity of solving its problems be-
fore the examiner, his consideration of this simple
device has led him into the computation of areas, into
a study of the principle of the lever, of moments of
forces, of the velocity of flow of steam and other
fundamental principles of mechanics. This applies to
those who have studied the subject intelligently, not
to those who have attempted to get over it by learning
a rule by rote, simply to be confounded when con-
fronted by another rule, or a case to which their rule
would not apply. The whole subject is so simple that
an hour's study will put a man in possession of the
fundamentals so that he can make his own rules or
solve any problem without a rule, from a sheer under-
standing of the principles involved,
PRESSURE PER SQUARE INCH
A cubic foot of water weighs, in round numbers,
62 pounds. If you can imagine ten cubic feet packed
one above the other, as in Fig. 49, they would make a
column weighing some 206 pounds, supported on a
75
7 6
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\
FIG. 40.
THE SAFETY VALVE 77
base one foot square, so that the pressure would be
620 pounds per square foot. The water in a tank or
pond may be conceived to be divided into columns of
this kind, and it will be seen that there will be a pres-
sure on the bottom of 62 pounds per square foot for
every foot of depth. But, in the square foot support-
ing this weight there are 144 square inches; and as the
pressure is evenly distributed, each square inch
carries: ,
62 -T- 144 = 0.43 of a pound.
for each foot in depth, and the pressure in the case of
the column 10 feet in hight would be 620 pounds per
square foot, or 4.3 pounds per square inch.
Just as the tank or pond could be conceived to be
divided into columns of one square foot section, each
square foot can be conceived to be divided into 144
columns of one square inch section, as shown in Fig. 49,
and each foot in hight of such column, like the piece
marked A, would weigh T | of the whole weight of the
cubic foot of which it is the T | part, and press upon its
square inch of base with a pressure of:
62 -f- 144 = 0.43 of a pound.
As this pressure in a liquid or gas is exerted in all
directions, it is evident that the pressure on the hori-
zontal piston in Fig. 50 would be 4.3 pounds per square
inch, and if it has an area of 30 square inches there
would be a force of:
4.3 X 30 = 129 pounds,
forcing the piston to the right; and since there is at a
BOILERS
116.1
Lbs.
a j b I
Depth in Pressure Ibs.
Feet persq.in.
r-0
0.43
0.86
1.29
5
10
1.72
2.15
2.58
3.01
3.44
3.87
4.30
FIG. 50.
THE SAFETY VALVE
79
depth of 9 feet a pressure of 3.87 pounds per square
inch the valve at the left would have 3.87 pounds
pushing upward on each square inch of its exposed
area, i.e., the area corresponding with the diameter
a b, and if that area were 30 square inches it would
t"i ICP *
30 X 3.87 = 116.1 pounds
to hold the valve closed against that pressure.
The steam gage shows the pressure per square inch.
If the gage points to the 100 mark it indicates that if
the pressure existing in the boiler Were exerted upon
one square inch of area, Fig. 51, it would push with a
force of one hundred pounds. If exerted upon an
l.Inch
Unch-
Unch J
FIG. 51.
FIG. 52.
FIG. 53.
area of one-half a square inch, Fig. 52, it would push
with a force of 50 pounds; upon an area J inch square,
or 1 of a square inch, Fig. 53, 25 pounds; upon an area
of one square foot, or 144 square inches, 14,400 pounds,
etc.
The force exerted by the steam to lift a safety valve
depends then upon the area of the valve as well as
upon the intensity of the pressure.
8o
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To FIND THE AREA OF A CIRCLE
The area of a i-inch circle is 0.7854 of a square
inch, the difference, 0.2146, between this and the full
square of the diameter being taken up by the corners,
Fig. 54. If the side of the square is doubled the area
V llnch -
-2 Inches- --
FIG. 54.
FIG. 55.
of the square will be multiplied by four, as is plainly
shown by Fig. 55, which obviously contains four
squares of the area of that shown in Fig. 54, although
its side is but twice as long; and it is equally evident
that the inclosed circle bears the same proportion to
the total area in both cases and that the shaded area
of the circle in Fig. 55 is four times that in Fig. 54,
although its diameter is but twice that of the smaller
circle. If we treble the length of the sides the area of
the square will be multiplied by nine, always the square
of the side, i.e., the side multiplied by itself.
THE SAFETY VALVE
81
The area of any circle may be found by multiplying
the area of a i-inch circle (0.7854) square inch by the
square of the given diameter.
In Fig. 55 the diameter is 2 inches and the area is:
2 X 2 X 0.7854 = 3.1416 square inches.
The area of a 4-inch circle would be:
4 X 4 X 0.7854 = 12.5664 square inches.
It may aid in remembering the factor 0.7854 to know
that it is one-fourth of 3.1416, the number by which
the diameter is multiplied to get the circumference.
The area of a triangle is obviously one-half the
product of its base and night. In Fig. 530 the product
FIG. 530.
FIG. 536.
FIG. 5 3 c.
of the base A B and the hight A C would be the area
of the rectangle A B C D and the shaded area of the
triangle is obviously one-half of this, for the two
unshaded portions put together would make a similar
triangle. This is just as true if the base is an arc of a
circle as in Fig. 53^, and just as true if the base incloses
the apex as in Fig. 53^. The circle is therefore a
triangle with a circular base 3.1416 times the diameter
82 BOILERS
or 2 X 3.1416 times the radius, and with a hight equal
to the radius, and its area (one-half the product of
hight and base) is:
A radius X 2 X 3.1416 X radius
Area = - -| = 3.1416 radius 2 ,
so that the area equals 3.1416 times the square of the
radius, and since the radius is one-half the diameter,
the square of the radius is the square of the diameter
divided by four:
Area = 3.1416 r 2 = 3.1416 = D 2 X ^^
4 4
= 0.7854 D 2 .
EFFECT OF PRESSURE IN LIFTING A VALVE
Suppose the 3-inch valve in Fig. 56 to be loaded
with six weights of 100 pounds each and that the valve
and steam weighed 30 pounds, what would the pressure
per square inch have to be to lift it?
The total weight to be lifted is 630 pounds. The
total upward pressure must equal this, and if 630
pounds is exerted on 7.0686 square inches (the area of
a 3-inch valve, see table) the pressure on each square
inch will be: ^
630 -T- 7.0686 = 89. i pounds.
How much load would have to be put upon the same
valve to allow it to blow off at 75 pounds per square
inch?
If the pressure exerts 75 pounds on one square inch,
it would exert on the 7.0686 square inches of the valve
which is exposed to it:
THE SAFETY VALVE 83
75 X 7.0686 = 530 pounds,
which must be the combined weight of the valve and
the weights with which it is loaded.
Fig. 56 does not show a practicable valve, but is
sufficient to illustrate the point that the force tending
FIG. 56.
to lift the valve must equal that holding it to its seat
(in this case the dead weight of the valve itself and the
weights with which it is loaded), and that this upwardly
acting force is the area of the valve in square inches,
multiplied by the pressure per square inch. Such a
dead-weight valve is ponderous and impracticable
8 4
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and the usual practice is to use a lighter weight, increas-
ing its effect by leverage, or to hold the valve to its
seat with a spring.
THE PRINCIPLE OF THE LEVER
Suppose a strip of board balanced over a sharp edge
as in Fig. 57. If equal weights be placed upon it at
h '
A
FIG. 57.
equal distances from the center it will still be in bal-
ance. If one of the weights be moved in half of the
distance to the point at which they are balanced, as
in Fig. 58, the other weight will have to be halved to
U 12 >!*- 6 *\
FIG. 58.
preserve the equilibrium. If one of the weights be
moved to one-third of its distance from the balancing
point, as in Fig. 59, the other weight will have to be
THE SAFETY VALVE 85
reduced to one-third of its original magnitude to pre-
serve the balance at the original distance.
A
FIG. 59.
Notice that in each case the product of a weight by
its distance from the point over which they balance is
the same as the product of the weight which balances
it and its distance from the same point. Suppose the
weights in Fig. 57 to be each 20 pounds, each at 12
inches from the center. Here obviously the weights
and distances being the same their products are equal:
20 X 12 = 240 and 20 X 12 = 240.
When the right-hand weight is moved in to 6 inches
from the center the other had to be reduced to 10
pounds: ,
10 X 12 = 1 20 and 20 X 6 = 120.
When the left-hand weight was moved in to 4 inches
from the center the other had to be reduced to 6:
6 X 12 = 80 and 20 X 4 = 80.
The same principle applies in Fig. 60, where the
force exerted by the man, multiplied by the distance
A B, must, if he lifts the machine, equal the pressure
with which the load bears on the bar at the point C,
86
BOILERS
multiplied by the distance B C of that point from the
point B around which the lever turns. In mechanics,
this point, the B of Fig. 60, is called the "fulcrum"
and the product of the load, weight or force by its
distance from the fulcrum is called its "moment."
In the case described by Fig. 57 the moment of each
FIG. 60.
weight is 240; in that of Fig. 58, 120; in that of Fig. 59,
80; in that shown in Fig. 60 the moment of the load is
the weight or force with which the load bears on the
point C, multiplied by its distance from the fulcrum B,
and the moment of the force is the force which the
man exerts upon the bar at A, multiplied by the dis-
tance of that point from the fulcrum.
Notice that in Fig. 61 the fulcrum is at one end of
THE SAFETY VALVE 87
the lever instead of between the load and force as in
the other examples. The principle is the same. The
fulcrum is the stationary point about which the load
and the force move. In Figs. 60 and 61 it is evident
that the shorter the distance between the load and
the fulcrum the less the man will have to exert himself.
\
FIG. 61.
The point to grasp and remember is that the mo-
ments must be equal in order for the force to balance
or lift the load.
Equal Moments Produce Equilibrium
There are four important things about a lever:
88 BOILERS
L -the load.
F = the force applied to balance or overcome the
load.
D t = distance of the load from the fulcrum.
D f = distance of the force from the fulcrum.
If any three of these are known the third can be
easily determined, for, as has been just explained,
Force X distance of force = load X distance of load.
P X D = L X DI
Moment of force = moment of load.
To find the force required to lift a given load:
FORMULA: T vx ^
RULE. Multiply tie load by its distance from tie
fulcrum, and divide by tie distance at which tie force is
applied from tie fulcrum.
To find the distance at which a given force must
be applied from the fulcrum to balance a given load:
FORMULA: T n
Df= ^-
RULE. Multiply tie load by its distance from the
fulcrum and divide by tie given force.
To find the load which may be lifted with a given
force :
FORMULA: r n
T r \ Uf
THE SAFETY VALVE 89
RULE. Multiply the given force by the distance of
its point of application from the fulcrum and divide by
the distance of the load from the fulcrum.
To find the distance at which a given weight or load
must be placed from the fulcrum to balance a given
force :
FORMULA: D = F X D/
Li
RULE. Multiply the given force by the distance of
its point of application from the fulcrum and divide by
the load.
THE LEVER SAFETY VALVE
Effect of the Leverage of the Ball
Suppose the weight instead of setting directly upon
1 i
FIG. 62.
the valve, as in Fig. 56, is applied through a lever, as
in Fig. 62. From what has preceded it will easily
go BOILERS
be seen that the weight multiplied by its distance
from the fulcrum will equal the force which it will
exert upon the valve stem multiplied by the distance
of its point of application from the fulcrum.
Weight
f
Distance
of ball
Pressure
of ball
i
1
Distance
of stem
of
ball
X
from
=
on
from
L/dll
fulcrum .
stem
I fulcrum .
Let the weight equal 75 pounds,
distance of weight from fulcrum 32 inches,
distance of stem from fulcrum 2f inches,
what will be the force exerted by the ball to hold the
valve to its seat?
Weight of ball X Distance of ball from fulcrum _
Distance of stem from fulcrum
Pressure of ball on stem.
Then the moment of the ball is:
75 X 32 = 2400 inch-pounds,
and:
2400 -f- 2.75 = 872.727 pounds
will be the pressure on the valve stem due to the ball
and the moments will be equal:
75 X 32 = 2400 and 872.727 X 2.75 = 2400.
Suppose this to be a 4-inch valve, the area of which
is 12.5666 square inches. The pressure per square
inch upon the under side of the valve necessary to
balance the effect of the ball would be:
THE SAFETY VALVE 91
872.727 ~ 12.5666 = 69.4 pounds.
This is the pressure at which the valve would blow
off if nothing but the ball were holding it to its seat.
It takes a little additional pressure to lift the valve and
to overcome the weight of the lever, as will be explained
later, but this is a comparatively small affair and
in usual approximate calculations is not taken into
account. Neglecting these we can make the follow-
ing simple
Rules for lever safety valve, neglecting weight of
valve, stem and lever:
Let W = weight of the ball,
D = distance of ball from fulcrum,
A = area of valve in square inches,
d = distance of stem from fulcrum,
P = pressure per square inch on valve which
will balance ball.
To determine the pressure on a valve of given
diameter required to balance a ball of given weight at a
given distance from the fulcrum.
F RMULA: W XD
P =
Axd
RULE. Multiply the weight of the ball by its dis-
tance from the fulcrum. Multiply the area of the valve
in square inches by the distance of its stem from the
fulcrum. Divide the first product by the second and the
quotient will be the pressure per square inch required to
overcome the weight of the ball.
92 BOILERS
EXAMPLE. The stem of a 4-inch safety valve is 2 J
inches from the fulcrum. Supposing the valve will blow
when the gage shows 7 pounds without any weight upon
the lever (i.e., that it takes 7 pounds per square inch on
the area of the valve to overcome its own weight, that
of the stem and the bearing effect of the empty lever),
at what pressure would it blow with a weight of 75
pounds (Fig. 62) 32 inches from the fulcrum?
BY THE FORMULA:
P W A^ D i = 7 77^ = 69-4 + 7 = 76.4 pounds.
A X d 12.5666 X 2.75
BY THE RULE:
Area of valve 12.5666 75 Weight of ball
Distance of stem 2.75 32 Distance of ball
628330 1 50
879662 225
251332
34.558^)2400.00)69.4 pounds.
This is the pressure required to lift the ball.' Adding
the 7 pounds required to blow the valve without the
ball, the' answer would be 76.4 pounds. Scratching out
the last three figures of the first product saves hand-
ling large numbers and does not materially affect the
result. If we called this 34.6 (nearer right than 34.5
because the 58 rejected is over one-half) the quotient
would still be 69.36.
To find the weight required to hold a given pressure
on a given valve:
THE SAFETY VALVE
93
FORMULA:
D
RULE. Multiply the area by the pressure and by the
distance of the stem from the fulcrum and divide by the
distance of the ball from the fulcrum. The quotient will
be the weight of ball required to balance the steam pressure
on the valve.
EXAMPLE. What weight of ball would be required
to allow the valve in the above example to blow off
at 80 pounds?
The ball must provide for 73 pounds per square inch,
the lever valve and stem taking care of the other
seven, so that P = 73 pounds.
BY THE FORMULA:
. y8 . 8 pounds .
BY THE. RULE:
73
Pressure
Distance of stem
376998
879662
917-3618
?75
45868090
64215326
18347236
Distance of ball, 32)2522.744950(78.8 pounds.
To find the position of the weight in order that it
may exert a given pressure on the stem :
94 BOILERS
FORMULA: _ AxPxd
W
RULE. Multiply the area by ihe pressure and by the
distance of the stem from the fulcrum and divide by the
weight of the ball. The quotient will be the distance at
which the ball must be from the fulcrum in order to produce
a given pressure on the stem.
EXAMPLE. If the original 75-pound weight had
been used, at what distance from the fulcrum would it
have had to have been placed to have allowed the valve
to blow off at 80 pounds?
BY THE FORMULA:
D . ^y = ".566x^73x3.75 = 3? 6 jnches .
BY THE RULE. The product of the factor in the
numerator is 2522.74495 as before, and dividing this
by 75, the weight of the ball:
75)2522.74495 (33.6 inches.
These simple rules will serve all practical purposes,
especially if it is borne in mind that P represents the
pressure with which the ball only bears upon the stem,
not including the weight of the valve, lever, etc., and an
allowance be made for these other effects as has been
done in the examples. A general idea of what the pres-
sure per square inch required to lift the valve, stem and
lever may be is given in column 8 of the table on page
119. It is well, however, to know how to make these
allowances accurately, and they will now be considered.
THE SAFETY VALVE 95
EFFECT OF THE WEIGHT OF THE VALVE
AND STEM
The pressure acts directly upon the valve and stem
without leverage, and must exert a force to balance
their weight equal simply to that weight, just as was
the case in Fig. 56.
Suppose the valve and stem of a 3-inch valve to
weigh 1.5 pounds, how much pressure per square inch
would be required to lift the valve from its seat?
Comparing Figs. 56 and 63, it will be seen that this
case is the same as the first example given in describing
the earlier cut. The total pressure on the valve must be
1.5 pounds, and if 1.5 pounds is to be exerted on 7.0686
square inches, the pressure per square inch will be:
1.5 -f- 7.0686 = 0.212 pound.
Column 3 of the table on page 119 gives roughly
the weights of valve and stem used on valves of the
standard diameters of three makers, and in connection
with column 4, which gives the pressure per square
inch required to lift the valves of the given weights,
serves to indicate the relative importance of this factor
of the problem.
THE EFFECT OF THE LEVER
The weight of the lever tends to hold the valve upon
its seat. It is evident that it would take a considerable
pull to lift the lever of a large safety valve with a cord
attached at the point at which the pin bears, as in Fig.
64, and this pull as measured upon a scale would be
9 6
BOILERS
the force which the valve would have to exert to push
the lever up. Every successive particle in the length
of the lever is acting with a different leverage, so that it
FIG. 63.
would at first appear a complicated process to calculate
this force; but a body acts in this respect just as though
its whole mass were concentrated at its center of gravity
and this makes the problem very simple.
THE SAFETY VALVE
97
If the lever be taken off and balanced over an edge,
as in Fig. 65, the center of gravity will be at the point
FIG. 64.
above the knife edge when the lever is balanced, and the
effect of the lever would be the same as if all the mass
were concentrated at that point.
FIG. 65.
Now find the distance of the center of gravity from
the fulcrum, from the point around which the lever
turns. This will be from the center of the hole when it
turns upon a pin, as in Fig. 66, or from the point where
it bears if a knife edge is used, as in Fig. 67; the dis-
tance a c in each case.
9 8
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In measuring for moments the distances must be
taken on a line passing through the fulcrum and at
o-
FIG. 66.
right angles to the direction of the force. In the case
of the lever safety valve the holding-down force is
FIG. 67.
gravity, which acts vertically. A line at right angles
to the vertical is horizontal, so that distances should
A B
FIG. 68.
be measured in a horizontal direction as through ABC,
Fig. 68, and not on the lines x x or y y.
THE SAFETY VALVE 99
In determining the distance a c, Figs. 66 and 67, do
not get bothered about the piece of lever which extends
back of the fulcrum. The more metal there is back of
this point the nearer the center of gravity is to the
fulcrum. If there were as much weight to the left of the
pin in Fig. 65 as to the right, the center of gravity
would be at the pin; the lever would balance over the
pin as it did over the knife edge and not bear on the
stem at all.
To apply this, suppose that the lever of a 3-inch valve
v/eighed six pounds, that the distance a c, Fig. 66, be-
tween the fulcrum and the center of gravity was found
to be 15 inches, and the distance a b from the fulcrum
to the point at which the pin bears 2\ inches. The
moment of the lever must be :
6 X 1 5 = 90 inch-pounds.
The moment of the lifting force must equal this, and
that moment is i\ times the force. Then the force
must be:
90 -f- 2\ = 40 pounds,
2-J- X 40 = 90 and 15X6 = 90.
Since a force of 40 pounds is to be exerted upon
7.0686 square inches, the force per square inch would
40 -v- 7.068 = 5.66 pounds.
The combined effect of the valve and stem and of
the lever of the 3-inch valve in question would be:
0.212 + 5.66 = 5.87 pounds.
Columns 5 and 6 of the table already referred to give
zoo BOILERS
the weights of levers and the distances of their centers
of gravity from the fulcrum as ordinarily found, and
column 7 gives the pressure per square inch on the valve
necessary to lift such levers. Column 8 gives the sum
of the respective values in columns 4 and 7, i.e., the
pressure per square inch required to lift the valve and
stem and the lever. It will be seen that the values run
fairly even for all sizes of valves, and that by using
seven or eight pounds as an allowance as in the above
examples, results can be attained with the simple rules
which will be within a pound or two of right.
SPRING-LOADED OR POP SAFETY VALVES
A rule for calculating the pressure at which a spring-
loaded valve will blow off is sometimes asked for.
There are none reliable that do not involve the deter-
mining by experiment of the force required to com-
press the spring, and if you are going to do this you may
as well determine by experiment at what pressure the
valve will, blow off. In practice nobody thinks of com-
puting the spring-loaded valve. If they want it to blow
off at 1 20 pounds they procure a suitable spring from
the makers and turn down upon the binding nut until
the valve will blow experimentally at the desired pres-
sure. The pressure at which a spring will yield depends
not only upon the shape and size of the material of
which it is made, the diameter, number, and pitch of
the coils, all of which are measurable and determinable,
but upon the nature and condition of the material itself.
You can readily appreciate that a spring of brass would
compress with less pressure than one of steel, similar in
THE SAFETY VALVE
101
every other respect, and that there is such a wide differ-
ence in steels that there will be a great deal of difference
in the action of steel springs according to the kind of
metal, degree of temper, etc. The best rule known is
the following:
To find at what pressure a valve will lift with a
spring of given dimensions and compression:
Multiply the compression in inches by the fourth power
of the thickness of the steel in sixteenths of an inch, and
by 22 for round or 30 for square steel. Product I.
FIG. 69.
Multiply the cube of the diameter of the spring,
measured from center to center of the coil (as on the line
d, in Fig. 69) in inches, by the number of free coils in
the spring, and by the area of the valve in square inches.
Product II.
Divide Product I by Product II and the quotient will
102 BOILERS
be the pressure per square inch at which the valve will
blow off.
The weight of the valve and of the spring should in
strictness be added to Product I, when the construction
is such that the valve supports the spring; but inasmuch
as the values 22 and 30 are guessed at it will not pay
to go into refinements in other directions. The result
of this rule has never been compared with an actual
valve. It is based on a formula adopted by a com-
mittee of Scotch engineers and shipbuilders. Corre-
spondence with the manufacturers of pop safety valves
as to the accuracy of the formula brings out the fact
that they proportion and calibrate their springs only
by experience and experiment. However, this rule
is given for what it is worth. If you have a spring-
loaded valve calculate it by this rule and see how nearly
it comes to the point at which the valve will blow off.
With a dead weight or a lever-loaded valve the force
required to lift it remains the same, no matter how high
the valve lifts. The weights weigh no more if they are
raised an inch or two, and the leverage does not change,
but with the spring-loaded valve the more the valve
lifts, the more the spring is compressed, and the more
force is required to compress or hold it. It follows then
that if an ordinary valve were loaded with a spring it
would simply crack open and commence to sizzle when
the pressure equaled the force at which the spring was
set, and that if this were not enough to relieve the boiler
the pressure would have to increase, opening the valve
more and more until the steam blew of? as fast as it was
made.
THE SAFETY VALVE
103
COMPLETE SAFTEY-VALVE RULES
It is evident that any complete rule for the safety
valve must include the separate treatment of the valve
and stem, the lever and the ball as factors in holding
the valve to its seat.
moment of ball
Moment of the
lifting force
moment of lever
moment of valve and stem.
The lifting force consists of the pressure per square
inch into the area of the valve, and its moment is the
product of the force by its distance from the fulcrum.
Expanded, then, the above becomes:
Weight of ball X distance of
its center of gravity from the
fulcrum
Pressure
X
Area
X
Distance of stem
from fulcrum
weight of lever X distance of
its center of gravity from
fulcrum
weight of valve and stem X
distance of their center of
gravity from the fulcrum.
In order to find one of these qualities we must know
all the rest, and consequently since the missing quantity
can be but on one side of the equal mark we can figure
the combined value of the quantities on one side of the
104
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equation (that is, in one set of brackets). Then we can
work out the operation indicated on the other side as
far as we can go. If the missing quantity is on the
left-hand side of the equation it can be found by divi-
ding the value of the other side of the equation by the
product of the two known factors on the left-hand side.
To find the pressure at which a certain valve will
blow off:
Multiply the weight of the ball, of the valve and stem
and of the lever, each by the distance of its center of gravity
from the fulcrum and add the products. Multiply the area
of the valve by the distance of its center from the fulcrum
and divide the sum above found by the product. The
quotient will be the pressure required.
Or more briefly:
Divide the sum of the moments of the valve, lever and
ball by the product of the area of the valve and distance
from the fulcrum.
EXAMPLE. At what pressure will a 3-inch valve blow
off with stem 2\ inches from the fulcrum, valve and stem
weighing i J pounds, lever weighing 6 pounds, having its
center of gravity 1 5 inches from the fulcrum and weighted
with a 48-pound ball 24 inches from the fulcrum?
Pressure
X
Area = 7.0686
X
Distance 2j
Product = 15.90435 j
48 X'24 = 1 1 52
6x15= 90
i.5X2i= 3.375
Sum of moments = 1245.375
1 2 45-375 - i5-9 435 = 7 8 -3 pounds.
THE SAFETY VALVE 105
This is all that we shall be likely to wish to find on
this side of the equation, for the distance of stem is
fixed and the area determined by other considera-
tions.
The other two things that interest us are the weight
of the ball and its distance from the fulcrum.
To find weight of ball or its distance from fulcrum :
Multiply the pressure by the area and by the distance
of the stem from the fulcrum. The product is the
moment of the force.
Multiply the weight of the valve by the distance of the
stem from the fulcrum; multiply the weight of the lever
by the distance of its center of gravity from the fulcrum,
and add the products.
Subtract 'the sum of the products just found from the
moment of the force, and the difference is the moment of
the ball.
Divide the moment of the ball by the weight of the
ball and the quotient is its distance from the fulcrum.
Divide the moment of the ball by the distance from the
fulcrum and the quotient is the weight of ball required.
EXAMPLE What weight of ball at the same dis-
tance would be required to allow the valve given in
the previous example to blow at 75 pounds, and at
what distance would the 48-pound ball there given
have to be placed from the fulcrum to produce the
same result?
io6
BOILERS
Moment
75
X
7.0686
X
21
of force 1 192.826
93-375
1099.451 mo-
rn e n t of
ball
Weight X distance of ball
+
6X15 - 90.000
+
1.5 X 2.25 = 3.375
93.375 sum
of moments,
valve and
lever.
= inches, distance of ball.
4b
1099.451 . .
- = pounds, weight of ball.
24
But the ideal valve should stay on its seat until the
pressure reaches the desired limit, then open wide and
discharge the excess. This result is accomplished by the
construction shown in Fig. 70. With the first opening
of the valve the steam passes into the little "huddling
chamber" made by the cavity near the overhanging
edge of the valve and a similar cavity surrounding the
seat. The pressure which accumulates here, acting
on the additional area of the valve, raises it sharply
with the "pop" which gives the valve its name, and
it is sustained by the impact and reaction of the issuing
steam until the pressure has subsided sufficiently to
allow the spring to overcome these actions.
The outside edge of the lower trough in the valve
shown is composed of an adjustable ring which may be
THE SAFETY VALVE
107
FIG. 70.
io8 BOILERS
screwed up or down so as to diminish or increase the dis-
tance between the overhanging lip of the valve and its
own inner edge, controlling the outlet from the chamber;
and diminution of pressure or the "blow back" required
to allow the valve to seat so that the valve opens wide
at a given pressure and seats promptly without sizzling
or chattering when the pressure has been reduced a cer-
tain amount depending upon the adjustment of the
ring. The various makers have adopted different
devices for adjusting the ring or other device for con-
trolling the outflow from the huddling chamber.
THE CAPACITY OF SAFETY VALVES
Let us next consider the capacity of valves; how large
a valve is required for a given boiler. Most of the rules
deal with grate surface and the area of the valve; the
rule adopted by the U. S. Board of Supervising In-
spectors being one square inch of valve area for each
two feet of grate area. That the valve should be pro-
portioned to the grate surface seems proper because
it is the grate surface, and not the heating surface,
which determines and limits the capacity of a boiler.
To a given grate surface, however, we should apportion
a sufficient amount of area of opening, and this area
of opening is not proportional to the area of the valve
but to the diameter and lift. A valve i inch in diameter
has an area of 0.7854 of a square inch, but that does not
mean that there will be an opening of 0.7854 of a square
inch for the steam to escape. If the valve is flat, as in
Fig. 71, the area opened for the discharge of steam
THE SAFETY VALVE 109
will be the circumference of the valve multiplied by
the lift. The circumference is
Diameter X 3.1416 (i)
and the area of the complete circle is
^. ,. Diameter
Diameter X 3.1416 X - (2)
4
and the area for the escape of steam is
Diameter X 3.1416 X Lift. (3)
When the lift is one-quarter the diameter, or
Diameter
the area for the escape of steam is the same as the area
of the circle; formula 3 is the same as formula 2.
FIG. 71.
When a flat valve has lifted a quarter of its diameter
it has reached the limit of its capacity to discharge
steam. It doesn't do any good to lift higher, for the
area around the edge of the valve is already as large as
the area of the valve itself and the capacity of the valve
is proportional to the area or the square of the diameter.
no BOILERS
In practice, however, the lift of valves is much less than
one-quarter of their diameter, and for a given lift the
area for the escape of steam is proportional to the cir-
cumference or the diameter rather than to the area.
Most of the rules, however, as above stated, allow a given
amount of valve area to a square foot of grate surface,
and make the allowance liberal enough to include all
conditions. For instance, the rule of the U. S. Board of
Supervising Inspectors calls for one-half a square inch
of valve area for each square foot of grate surface. A
4-inch valve has about 12 square inches of area and
would thus take care of 24 square feet of grate. It
would not be possible to burn over 25 pounds of coal
per square foot of grate per hour with natural draft,
nor to evaporate over 12 pounds of water with a pound
of coal, so that the boiler could not possibly make more
than
25 X 12 X 24 = 7200 pounds of steam per hour,
or
7200 -T- (60 X 60) = 2 pounds of steam per second.
Now the weight of the steam which will escape through
a given aperture per second is given by the following
f rmUla: wt P^ssure X Area
70
that is, the weight in pounds which will escape in a
second is equal to the absolute pressure in pounds per
square inch multiplied by the area in square inches and
divided by 70.
THE SAFETY VALVE in
On the other hand, the area required to discharge a
given weight is Wd h
Area = -
Pressure
that is, the weight in pounds to be discharged per
second multiplied by 70, and divided by the absolute
pressure equals the required area. Now we have found
that with a rate of combustion practically impossible,
with natural draft, and a practically unattainable
evaporation per pound of coal, the most steam that the
boiler with 24 square feet of grate suface could furnish
is 2 pounds per second. The area required to discharge
this at 70 pounds pressure, absolute, is
2 X 7O
= 2 square inches.
70
The 4-inch valve which this boiler would require
would have a circumference of practically 12 inches,
and would need to lift only one-sixth of an inch to
furnish the two square inches of opening necessary
to discharge the steam, for
12 X J = 2.
One-sixth of an inch is only one twenty-fourth of
the diameter of the valve. You see that this simple rule
gives an ample margin, requiring but a small lift to
discharge more steam than the boiler can possibly make.
It is altogether useless and nonsensical to figure the
areas of opening to four places of decimals involving
with beveled seats complicated operations with sines
and cosines, in a calculation which involves no accuracy
112 BOILERS
but which requires simply a result which shall be amply
large to cover any emergency likely to be encountered
in practice. It is like trying to measure the distance
to the next town in feet and inches, in order to answer
a man who would be abundantly satisfied to know that
it was about three-quarters of a mile. You may be
sure that a valve which has a square inch of area for
each two square feet of grate surface will liberate all the
steam that can be made by the coal that you can burn
on that grate surface, so long as the valve is free and
in good condition. It is quite probable that a smaller
valve would do, but in a matter of this kind we want
to provide not the smallest that will possibly do but
enough capacity to be absolutely safe. For all purposes
of ordinary practice, therefore, divide the grate surface
by 2, which will give you the valve area required and
you can find the corresponding diameter by multiply-
ing the square root of the area by 1.128. Don't carry
your decimals out too far because you will have to take
the nearest commercial size after all.
Here is a rule which will give you the diameter of
the valve in inches at once:
Multiply the square root of the grate surface by 0.8.
This would be particularly handy when the grate is
square, or nearly so, for then the length would be the
square root of the area.
You can see how the rule is made, or rather, makes
itself.
By the supervising inspector's rule the valve area
required equals the grate surface divided by 2.
THE SAFETY VALVE 113
A grate surface
Area - .
The diameter is the square root of the quotient of
the area divided by 0.7854.
TV , / area
Diameter =
0.7854*
And since in this case the area equals one-half the grate
surface the diameter will be the square root of one-half
the grate surface divided by 0.7854.
. /grate surface.
Diameter = \/ - 5
V 2 x 0.7854
Diameter = ./grate surface
V 1.5708
We can get rid of the square root in the denominator
by finding it once for all. It is 1.25 very nearly. So
our formula becomes
TV Vgrate surface
Diameter = -
1.25
Dividing by 1.25 is just the same as multiplying by
T.^y, and as T is = 0.8, the multiplication is easier, so
we have /
Diameter = V grate surface X 0.8.
The grate surface will never be so large that the
square root cannot be easily determined with sufficient
accuracy mentally. If it is between 25 and 36 the root
is between 5 and 6. The square of 7 is 49, of 8, 64, etc.,
so that by trial the root can be determined approxi-
H4 BOILERS
mately. Here is an easy trick to get the square of a
number with two figures ending in 5 :
Multiply i plus the left-hand figure by the left-hand
figure, and annex 25 to the product.
What is the square of 35?
The left-hand figure is 3. Three plus i is 4, and 4 X
3 = 12. Annex 25 and get 1225.
This rule works just the same when the 5 is a decimal,
only in that case the annexed 25 is a decimal too, and
will enable you to determine instantly by inspection
the nearest number advancing by halves to the square
root. As the sizes of safety valves advance by half
inches, the nearest root determined in this way will be
sufficiently accurate, as we have to take the nearest
commercial size anyhow.
What is the square of 6.5?
Six plus i = 7; 7 X 6 = 42; add 25, which in this
case will be a decimal fraction, there being two places
to point off, and get 42.25.
In this way you can square 1.5, 2.5, 3.5, etc., and
this is as near as it is ever necessary to get a root in the
above formula. Suppose, for instance, you had 58
square feet of grate surface. What is the square root?
Seven times 7 = 49, and 8 X 8 = 64. It must be
between 7 and 8; 7.5 X 7.5 = 56.25.
That is near enough to 58. The square root of 58
is really 7.61 5. Multiplying this by 0.8 we get 7.61 5 X
0.8 = 6.092, which is practically a 6-inch valve. We
should have got at the same result if we had taken the
square root as 7.5, for 7.5 X 0.8 = 6.
When the grate surface is over 30 or 40 feet it is
THE SAFETY VALVE 115
better to get the required capacity by putting on two
valves than by using one large one. In fact it is a
pretty good plan to have two safety valves anyway.
There is a great deal of responsibility on that little
appliance, and many of the most destructive of boiler
explosions would have been avoided by an operative
safety valve of sufficient capacity. So many little
things can occur to make it hold against a destructive
pressure, even when the attendant follows the usual
directions to raise it from its seat daily, that prudence
dictates the use of an auxiliary valve. It would be a
remarkable coincidence if both stuck at the same time
without criminal negligence.
The amount of opening of an ordinary lever safety
valve is determined by the amount of surplus steam
to be delivered. If the boiler is making more steam
than is to be taken out of it the pressure will increase,
and when it reaches an amount sufficient to overcome
the weight of the ball, etc., the valve will be raised
a little from its seat and the steam will escape. If the
opening thus afforded is sufficient with the other drafts
on the boiler (such as the supply to the engine, etc.)
to allow all the steam the boiler is making to escape,
the valve will not open any wider, but if not the pressure
will continue to increase and force the valve open
until the steam can escape as fast as it is made. As
the surplus production of steam decreases, as by closing
the dampers or a greater demand by the engine, the
valve gradually settles down to its seat again.
On account of its greater lift and effective discharging
area the pop valve is allowed by the Board of Super-
Ii6 BOILERS
vising Inspectors three square feet of grate surface
per inch of area instead of two, as with the ordinary
lever valve.
We have seen that the escape of steam through an
opening of given size is proportional to the absolute
pressure. Twice as much steam will go out of an inch
hole in a minute with 190 pounds behind it as with
95 pounds. It is presumed, for this reason, that the
inspectors only require a square inch of valve area for
every 6 feet of grate surface on boilers carrying a steam
pressure exceeding 175 pounds gage.
It has been said that although the area effective for
the escape of steam is not proportional to the area due
to the diameter of the valve, and although the latter
area is that used in the formula for capacity, the allow-
ance is so liberal that it is practically useless to figure
the former. It may be interesting, however, to know
how to figure it, and a treatise on the safety valve
would hardly be complete without directions for so
doing.
With a flat valve we have already seen that the area
for the escape of steam is the lift of the valve. multiplied
by its circumference. With a bevel-seated valve in
which the valve does not lift out of the seat the area
A A, Fig. 72, is that of a frustum of a cone, Fig. 73.
Now to find this area the rule is to add the circumfer-
ence of the greater circle to the circumference of the
lesser CD; divide by 2, and multiply by the slant hight
C A. In other words, to multiply the average length
of the strip which would be made by flattening this
surface out by the width of that strip. To work this
THE SAFETY VALVE
117
rule out would take us too far into trigonometry, but
the rule follows:
(i) Multiply the diameter of the valve by the lift, by
the stine of the angle of inclination and by 3.1416.
FIG. 72.
(2) Multiply the square of the lift by the square of
the sine of the angle of inclination, by the cosine of this
angle and by 3.1416.
(3) Add these two products.
The U. S. rules require a bevel of 45 degrees, and
most valves are made with seats of that degree of in-
clination. For such a valve the rule becomes:
(i) Multiply the diameter of the valve by the lift and
by 2.22.
n8 BOILERS
(2) Multiply the square oj ihe lift by i . 1 1 .
(3) Add these two products.
When a valve with a beveled seat lifts clear of the
seat as a valve with a slight bevel may, the area of
the opening is computed by the above rule for a lift
which would raise it to the upper level of the seat, and
to this is added the circumference of the valve multi-
plied by the lift above the seat level.
THE SAFETY VALVE
119
2
3
4
1,1
3 >
Area
of
Valve
Weight of Valve
and Stem
Pressure Required to
Valve and Stem
Lift
In.
Sq. In.
Pounds
Pounds per
Sq. In
I
o.i 104
0.125
0.131
I
0.1963
0.156
O.
< 4
o-7947
0.713
a
0.441
8
0.187
0.
23
0.423
c
521
I
0.7854
0.187
o.
34
0.238
0.432
i\
1.2272
0.312
0.60
0.254
0.488
I 2
1.76"
i
0-437
0.
75
0.247
C
424
2
3-M
6
0-542 i..
6a
5
0.
)7
0.172
40
C
.308
2*
4.9087
0.8395 2.75
1.69
0.171
0.560
0-344
3
7.o6
16
1-339 3-.
o
2.
53
0.189
40
c
329
3-V
9.62
i
1.8 4-'
r,5
2.
io
0.187
o
40
I
c
.270
4
12.5666
2-371 5-'
.s
4-
t2
0.189
0.458
0.327
4*
15.904
I
3-0 6.'
s
5.
[8
0.189
o
.42,
I
c
.326
5
19-635
o
4.125 9.'
s
6.
4S
0.210
o
49
c
324
6
28.2744
5.87 11-875
8.62
0.208
o
420
0.305
5
6
7
8
Distance of Center of
Weight of Lever Gravity from
Fulcrum
Pressure Required
to Raise Lever
Pressure Required
to Raise Valve,
Stem and Lever
Pounds
Inches
Pounds per Sq. In.
Pounds per Sq. In.
0.125
3-25
5-89
6.003
0.140
0.20 3.0
6
25
2
Ss
8.49
3-6^
47
9-203
0-343
0.38 4.812
9.0
4.98
10.32
5-403
10.841
l.O
0.48 7-75
9
o
8
32
5-50
8.5
;
5-932
1.125
0.65 7.312
8
Si 2
5
5
OS
3-73
5-9<:
>4
4.218
0-875
0.87 6.875
IO
125
2.87
3-63
3-II7
4-054
2-5
2.O
1. 12 I3-3I2
14.56
i i
so
7
37
7-42
2-43
7-5'
.2
7-92
2-738
3-5
3-562
4-0 15-25
16.37
tS
O
5
70
5-59
7.24
s.o<
)I
6.15
7-584
4-75
5-8i2
6.0 18.625
17-37
10
25
6
07
6.35
7.07
6.8
SO
6.84
7-399
5-75
8.25
10.50 21.75
19.0
10
25
5-78
6,52
9.08
5-967
7.01
9-350
6.0
12.875
13.0 23.0
22.
23
4
7,S
8.20
8-75
4-9<
)0
8.66
9.077
7-o
13-125
i8.o 22.125
23.0
26.75
3-89
6,33
11.09
4.079
6.75
11.416
10.75
18.25
20.0 25.25
25-5
31
25
5
S i
7.22
10.62
5-7'
I
7.72
10.944
15.0
21.25
32.0 27.5
29.62
37-25
5-56
6.36
12.05
5.768
6.78
12.355
9
10
Length of Lever
Distance of Stem from
Fulcrum
Weight of Ball Ordinarily
Furnished
Inches
Inches
Pounds
6.31
0.62
1-56
5-62
12.5
0-75
o-75
3-2
2.0
9-50
18.0
0-75
c
75
5-5
2.6
14-87
18.0
1.19
1.0
8.12
4-8
14.4
17-625
1.19
]
25
9.62
I l.O
13-4
20.25
1.19
]
37
15.37
14.0
26.1 29.50
23-0
1.44
I
87
1.687
19.0
30
24.0
30.0 33.0
30.0
1.87
2
i
l
]
.687
29.0
45
34-5
37-12 35.0
38-5
1.87
2-25
2.312
38.0
63
50-5
43-i 38-3
75
38-5
2.25
s
3
2
.312
48.5
ss
67.0
45-5 44-5
46-5
2-37
2-75
2-75
70.0
110
86.5
43.75 46.1
25
53-5
2-5
3
o
2
75
83.0
I
40
86.5
49.87 51.5
62.5
2-5
2
">
" 4
.0
98.0
I
68
103.0
54-5 59-50
74-5
2.625
3-50
3-5
139.0
220
139.0
X
HORSE-POWER OF BOILERS 1
IN a recent catalog of a well-known maker of engi-
neering specialties the following approximate rules
for calculating the horse-power of various kinds of
boilers were noticed and copied. The rules are in-
tended for use in determining the proper sizes of
injectors and other apparatus when the exact dimen-
sions or heating surface of the boiler is unknown or
hard to obtain:
KIND H. P.
Horizontal Tubular = Dia. 2 X Length -r- 5
Vertical Tubular . . == Dia. 2 X Hight -T- 4
Flue Boilers == Dia. X Length H- 3
Locomotive Type = Dia. of Waist 2 X
Length over all -r- 6.
All dimensions to be in feet.
In the first and third cases the length is the length
of the tubes or that of a "flush-head" boiler and does
not include the extended smoke-box. In the second
case, the hight is that of a plain vertical boiler in which
the upper part of the tubes is above the water line;
it is not the hight of a boiler with submerged tubes.
1 Contributed to Power by C. G. Robbins.
120
HORSE-POWER OF BOILERS 121
The extreme simplicity of the rules aroused curiosity
as to their accuracy, and comparisons were made
between manufacturers' ratings and ratings calculated
by the formulas above. The results are given in the
accompanying table. They agree very closely, except
in a few of the larger sizes of tubular boilers, where the
calculated rating falls below that of the manufacturer.
And in these sizes it will be noticed that the heating
surface per horse-power is less than in the smaller sizes
where the two ratings practically agree.
It is quite possible that the ratings of other manu-
facturers would show a better or worse agreement.
In any event, the rules prove to be valuable for just
what is intended and will save considerable trouble in
measuring up and calculating the power of existing
boilers when ordering injectors, feed pumps, and the
like.
122
BOILERS
M *t O O
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Diameter (inches) X Length (feet)
Heating Surface
Manufacturers' Rating
Rating bv Rule
K
Diameter (inches) X Length (feet)
Heating Surface
Manufacturers' Rating
Rating bv Rule
Diameter (inches) X Hight (feet)
Heating Surface
Manufacturers' Rating -
Rating bv Rule
Diameter (inches) X Length (feet)
Heating Surface
Manufacturers' Rating
Rating by Rule
Waist Diam. (in.)X Length (ft.) J4oX
Heating Surface 26
Manufacturers' Rating 2
Rating by Rule 2 s
XI
BOILER APPLIANCES AND THEIR
INSTALLATION .
IN this paper it is my aim to briefly point out a few
of the deficiencies which not only exist in so many
of the less modern plants located in isolated places,
but which are too often found in the large and perhaps
otherwise well-equipped plants.
First in importance is the safety valve, which in
some instances can be called such in name only, for
in their neglected or overloaded condition they would
not in any sense answer the purpose for which they
are intended. We still find a few engineers who per-
sistently stick to the old-style lever and weight safety
valve for what reason, we cannot say, unless it is
because they can be overloaded more easily than the
more modern spring-loaded pop valve. Certainly
everything else is in favor of the pop valve, especially
in the hands of incompetent persons, for the most
successful design of any steam appliance is that one
which is absolutely fool-proof. From the fact that
they can be locked and made fool-proof, that they are
much more reliable in their action and so much less
wasteful of steam, it is believed they will soon be
used universally, and that the lever valve will be a
123
124 BOILERS
thing of the past. But with all their advantages they
will not relieve the boiler of over-pressure unless
properly installed and kept in operative condition.
Boilers have been seen equipped with these valves
ample in size to take care of all the steam the boiler
could generate, and then the discharge opening re-
duced to one-third the area of the valve and piped up
through the roof. Again, as many as four 72x18
boilers have been seen all equipped with 4-inch pop
valves, and all piped to blow into one continuous 4-inch
header, which extended through the wall. There is no
serious objection to piping the waste steam from a
safety valve out of the building, when properly done,
but the better plan would be to have a suitable ven-
tilator in the roof, and let them discharge in the
building. There are, however, many plants where this
cannot be done. If the waste pipe is run out of the
building, it should never be smaller than the valve
itself, and if it is necessary to carry it any great dis-
tance, 20 feet or more, the pipe should be increased one
size and connected up with as few turns as possible.
It is also a very dangerous plan to run a waste pipe
direct from the safety valve horizontally some dis-
tance, and then run a vertical pipe up through the
roof, unless the pipe is properly supported to not only
sustain its own weight, but to carry the downward
thrust due to the reaction of the steam, which would
in turn throw a severe strain on the casing of the
valve and the flange bolts. The amount of pressure
so exerted is of course a matter of conjecture, for the
full boiler pressure could hardly be expected to be
BOILER APPLIANCES 125
realized on the waste pipe. However, serious acci-
dents are known to have happened from just such
construction, therefore they are not mere possibilities.
It is also quite necessary that the waste pipe be sup-
plied with the proper opening for free and continuous
draining, and not depend altogether on the drip open-
ing on the valve itself.
Next in importance to the safety valve is the water
column and its connections. There are probably
more accidents to boilers traceable to defective water
columns than to any other one cause. On a recent
visit to a new plant where three 150 horse-power
boilers were being installed, the water columns were
found piped up with f-inch pipe, with several turns in
the lower connection and with no blow-off pipe.
With some feed waters this would probably answer
the purpose, but water used for boiler purposes is
often found which would close up the lower connec-
tion in a very few days' run. In this case, as in many
others, the boiler makers were at fault, as they were
furnishing the attachments. Water columns should
never be connected up with pipes smaller than ij
inches, and in general practice ij-inch pipe is better,
but in every instance the lower connection should be
provided with a f-inch blow-off, and for convenience
should be piped to discharge into the ash-pit. This
blow-off may be provided with any good valve or
cock, but if the latter is used, a closed end wrench
should be provided, as an adjustable wrench is too
apt to be carried away and the blowing out neglected.
The removable disk Y-valves now on the market have
126 BOILERS
been found very serviceable and reliable for boiler
blow-offs, and no doubt they would be equally as good
for water columns. There is quite a difference of
opinion among engineers as to the advisability of
placing stop valves in the column connection, but
there is no real good reason advanced why they should
be so equipped. Many plants with valves in both
the lower and upper connections are found, but
it is not a misstatement to say that one-half the
lower valves can be found in an inoperative condition,
owing to the accumulation of scale on the seat and
valve. The less the number of attachments which
may prove a source of danger the better. In connec-
ting up water columns it is a good plan to use crosses
in the lower connections, plugging the unused open-
ings with gun-metal or brass plugs. These will be
found very convenient for removing deposit which
may accumulate and cannot readily be blown out.
Water columns are often too small to give the best
results. The chamber should be at least 3 inches,
and preferably 4, in diameter, internally.
Ignorance is also often displayed in placing water-
columns. A column placed too high is fully as danger-
ous in the hands of some men as one placed too low.
In plants with the columns so placed it has been ob-
served that when the water was just visible in the
bottom of the glass there would be 6 inches of water
above the top of upper row of tubes. The fireman,
knowing this fact, will carry the water low in the glass,
and if by chance the water should disappear from
view altogether, he will tell you that it just went out
BOILER APPLIANCES 127
of sight, and will then proceed to speed up the boiler
feed pump. A better and safer plan is to set the
column with the bottom of the glass just level with the
top of the upper row of tubes, then pull or cover the fire
before the water leaves the glass, in case of the failure
of the water supply. Gage-glass valves and try-cocks
are also too often neglected. While it is believed there
is no better way of ascertaining the hight of water in
boiler than by blowing out the water column and
then noting the rapidity with which water returns to
the glass, do not neglect the try-cocks, for the water
glasses will break and at times when it is not con-
venient to replace them; then the try-cocks will come
in handy, and should be found in working order.
The steam gage is next in importance, but, as a rule,
receives little attention. The dial on the factory
clock is kept clean, so there will be no mistake in read-
ing the time when the whistle should be blown; but
with the gage it is different; it has no such important
duties to perform. A steam gage is not the delicate
instrument that some would believe. However, their
accuracy is easily destroyed, if not properly connected
up. They should not be attached to the breeching
or boiler front, unless protected from the heat, and
they should be provided with a water trap to protect
the Bourdon spring from the heat of the live steam;
otherwise they will not give correct readings, and may
be ruined altogether. The best form of trap is one
made up of nipples and fittings, with a small drain
cock placed in the lowest point of trap for the pur-
pose of blowing out and of draining, to prevent freez-
128 BOILERS
ing in winter. A trap of this kind will be found much
easier to clean, in case of stopping up, than the bent
pipe.
NOTES
The use of cast-iron flanged nozzles connecting
boilers to steam pipes is being superseded by dropped
forge steel flanges. The former are objectionable,
for the rivet holes must be accurately drilled and the
curve must be a neat fit to the boiler plate or a calking
gasket be provided to make the joint tight. Then
such flanges will fail by fracture in riveting after
some time and money has been spent on the job. If
the cast nozzle is flanged to receive the steam pipe,
the holes for bolts must be drilled out and bolts go
with the nozzle. Many buyers object to superfluous
flanges as that much more for the engineers to care for
and pack. Then if the plant be a one or two boiler
one the best plan is to have no flanges between the
boiler and the main steam valve, for if a flange blows
out the packing one can readily shut the main steam
valve and repack it, while on the other hand one will
wait until the boiler cools off. With regard to strength
of material, while cast iron can be made, and un-
doubtedly is, to run as high as 25,000 pounds tensile
strength, the fact is it may run less than that, and in
calculating averages must be taken, which doubtless
will not exceed 15,000 pounds per square inch. In
addition allowance must be made for shrinkage strains
in such castings; usually an unknown amount, but
allowance should be given. If the flange be threaded
the strength of such threads will of course not equal
BOILER APPLIANCES 129
threads in forged steel. The expansion of the boiler
shell sets up strains on these flanges, and while cast
iron resists bending or flexure well, that is of no special
value, as the strains are continuous and unavoidable.
On the contrary dropped forged steel flanges furnished
in all pipe sizes and to fit practically any required
circle are now made and kept in stock by boiler supply
houses, ready for attaching and tapped to size.
The tensile strength equals flange steel. Granting
cast iron 15,000 tensile strength and forgings 60,000,
note the wide difference in strengthening by rein-
forcement of the hole cut in the boiler shell. The
steel flange may have rivet holes punched to within
J-inch of size and reamed out without damage. It
will "give" in fitting and riveting to the shell and no
gasket is needed. A Fuller calking tool will quickly
close any leak at the seam, but such rarely occurs,
as it is forged on a smooth die. The threads are ij
inches deep on a 6-inch size, and are very strong.
From all of the above, proved by experience, the steel
flange is vastly better than the cast-iron one. Never-
theless many old men will not accept anything other
than the latter, doubtless due to their opinions hav-
ing formed and "froze in" years ago.
The foregoing applies to a large extent to cast-iron
man-head frames, but as such are of larger size it is
clear that the strains due to shrinkage and expansion
under working pressure must be kept in mind as the
casting is narrower at the cross-section of the minor
ellipse than at major. Presuming the casting projects
upward and inward to receive the plate, the usual
130 BOILERS
type, it is likely shrinkage strains occur at the corners
of the angles. Considering the large amount of the
shell cut away for an 11X15 inch man-head, and allow-
ing 15,000 tensile strength for castings, it is often the
case that the weakest link in the chain composing the
strength of a boiler is at this point. In my opinion
engineers, designers and boiler makers should abandon
cast-iron man-head frames, if for no other reason than
to strengthen the boiler. Such frames should be, as
high-class shops now use, weldless flange steel, forged
into shape and double-riveted to the shell plate. No
one thus far has seen a cast man-head frame double-
riveted to the shell. Please note that point.
With an elliptical steel frame to save packing and
also profanity, a J-inch ring should be shrunk on
to the inner flange and planed off to give a seat one
inch wide. But if packing costs money, then in the
man-head plate have a groove provided so the packing
cannot be forced out, and a piece of asbestos f rope
with plumbago and oil when the joint is opened will
last two years. In one case with two boilers washed
out every two weeks it cost $3.00 each opening for
gaskets. The old plates were on my advice replaced
with new ones grooved and the cost for gaskets re-
duced from $78 per annum to $2, a thrifty saving by
the way.
Returning to the strength of the steel frame, it is so
superior to the cast one in every manner that no com-
parison can be made. Nor indeed is it necessary to
buy one particular type, as while these frames are
patented, several being of about equal merit, prices
BOILER APPLIANCES 131
are not kept at a high point. In view of the failures
in riveting castings and including drilling it is doubt-
less true the steel frames like the steel nozzles are
cheaper to the builder, while in every way each should
be more desirable to the buyer, the engineer and the
insurance companies.
To a large extent the above applies with equal truth
to pressed steel lugs or brackets supporting the boiler,
but in addition in shipping a boiler, while a steel lug
may by transit be bent, it can easily be straightened
and without injury a valuable quality. When a
boiler is set, the lugs being out of sight are out of mind.
As the walls transmit heat it is clear the lugs become
quite warm, for it is usual to protect them by the
thickness of only one brick, and as the lug is covered
outside, the heat is not lost but retained. More pro-
tection should be given under a lug, at least two courses
of brick and an air space be open above the lug.
Reverting to strength, note that it is usual to have
a space of 4 inches between the boiler and the side
wall, and by properly carrying the brick out to the
boiler the weight is transmitted over the entire seat of
the hig. On the other hand, if this is not done, then
one must make the lug stronger to allow for the 4-inch
span. When of cast iron, we cannot, as stated, accept
more than 15,000 pounds tensile strength per square
inch, while if of steel we can take 60,000 tensile strength
as the ultimate strength. Hence a |-inch steel equals
a i -inch casting; but the lugs are made, if of steel, of
equal width with ordinary cast-iron lugs, and in addi-
tion the pressed ribs make it much wider. It is usual
132 BOILERS
to have such lugs of f-inch plate, equaling castings of
i inches in strength. Steel lugs are easily punched
and fitted to boiler shells. There is life in them, as
before reaching a breaking point through overload the
give would be noticeable, while the casting would fail
without warning.
From all of the above you will doubtless agree that
in the modern steam boiler steel is winning its fight
over cast iron through its superiority in strength and
its adaptability for these purposes. In the up-to-
date shops these arguments plus actual reduction in
costs have led to its adoption.
XII
CARE OF THE HORIZONTAL TUBULAR
BOILER 1
ALTHOUGH the boiler room is the very heart of every
steam plant, it is frequently the subject of the grossest
neglect, and the instances in which it receives the care
and thought to which it is entitled are very rare.
Under the very best of conditions it is wasteful, but
in a great many, in fact in the majority of cases, it
is much more so than there is any necessity of. It
must be admitted that the boiler room is necessarily
a rather dirty and uninviting place, but that is no
excuse for neglecting it.
In the engine room every possible economy is prac-
tised. Every foot of steam pipe is covered; the best
grade of oil is used; the engine valves are set with the
greatest care; belts are run as slack as possible; and
many other points are watched in order to keep the
steam consumption down to the lowest possible point.
This is all very proper and good, and should be en-
couraged as much as possible, but in many cases far
more serious losses are permitted in the boiler room,
and it is these which can and should be stopped.
1 Contributed to Power by M. Kennett.
133
134 BOILERS
A COMMON SOURCE OF Loss
A very common source of loss is the leakage of cold
air through cracks in the settings. When flat plates
from one side wall to the other are used over the rear
of the combustion chamber, it is not unusual to find
a space of from J to i inch between the rear boiler
head and the plate. This admits a large quantity
of cold air to pass directly through the upper tubes,
which are the most valuable for generating steam.
As a rule these openings are not caused by faulty
setting of the plate, as these are usually well set,
making a tight joint, before the boiler is fired up.
But when the boiler becomes heated and expands, the
plate is forced back, and when the boiler cools, a small
space is left between it and the plate. Pieces of mortar
and chips of brick lodge here, and when the boiler is
again fired up and expands, the plate is forced still
farther back. It is practically impossible to prevent
these openings with this style of plate, but matters
can be greatly improved by packing the crack loosely
with waste which has been filled with soft fire-clay,
as this forms an elastic packing which will not readily
burn out.
The style of arch shown in Fig. 74 is practically free
from this objection as it rests against the boiler head
and follows its movements. This plan is open to the
objection that the angle iron on the boiler head finally
burns out, and in order to replace it the studs have to
be removed from the head, and new ones put in, with
the attendant trouble of making the job tight. Bear-
CARE OF THE HORIZONTAL TUBULAR BOILER 135
ing bars are sometimes built into the side walls as a
substitute for these angle irons, but they soon burn
out, also. All trouble from this source may be over-
come by using an extra heavy pipe as a bearing bar,
and making it part of the feed line, so that water is
being constantly pumped through it. Or, as in one
case in mind, a small open tank may be provided for
this purpose, the water circulating by gravity.
Numerous other cracks are constantly developing
in various parts of the settings, and should be kept
well filled with clay.
The combustion chamber back of the bridgewall
should not be allowed to become filled with ashes to
such an extent as to impede the draft.
PROPER DEPTH OF COMBUSTION CHAMBER
There is a great difference of opinion concerning the
proper depth of this chamber, some engineers claiming
that it should be filled up level with the bridgewall,
while others claim it should be quite deep. Much
depends upon the kind of fuel used, the writer believing
that when soft coal is used, it should be fairly deep to
allow the unburned gases to become thoroughly
mixed with the air and burn. An excellent plan is to
slope the flame bed from almost the hight of the bridge-
wall to the ground in the rear, and pave it with fire-
brick. This brick paving becomes incandescent and
ignites the gases and also reflects the heat upward toward
the boiler. This style of chamber is easily cleaned out
through a door in the rear wall at the level of the floor,
and the ashes should be raked out every day.
136
BOILERS
CARE OF THE HORIZONTAL TUBULAR BOILER 137
Do not make the mistake of placing this door one
or two feet above the ground, as is frequently done,
thus making it necessary to enter the chamber to clean
it.
The hight and form of the bridgewall are also worthy
of consideration. The principal object of the bridge-
wall is to keep the fire on the grates, and it should
not be built up too close to the boiler, nor should it
be curved to conform to the circle of the boiler shell.
Such walls tend to concentrate the intense heat in the
fire-box. This burns out the fire-door linings, and
increases the danger of burning the fire-sheet, in case
scale or sediment collects on it. They also prevent
the free passage of a sufficient quantity of air into the
combustion chamber to burn the gases.
We believe that all bridgewalls should be straight
and not closer to the shell than 12 inches for 48-inch
boilers, and 20 inches for y2-inch boilers. In many
cases we believe these distances may be increased with
advantage.
The necessity of keeping the tubes free of soot is
pretty well understood, and this point usually receives
proper attention. In addition to the usual blowing
out with the steam blower, however, they should be
thoroughly scraped at least once a week. The steam
from the blower condenses to a great extent before
reaching the rear end of the tubes; a great deal of the
soot is simply moistened and left adhering to the
tubes and soon burns into a hard scale which can only
be removed by a thorough scraping.
138 BOILERS
IMPORTANCE OF CLEANING BOILERS
Generally speaking, there are few operations about
a steam plant which are so badly neglected as the
cleaning of the boilers. The operation too often con-
sists simply of letting the water out, removing the
lower man-head, and washing the mud out with a hose.
The natural result is that the heating surfaces, espe-
cially the tubes, become heavily coated with scale.
This accumulates most rapidly at the rear head, and
the space between the tubes soon becomes entirely
choked for a short distance, preventing the free access
of the water to the tube-sheet. This causes the tube
ends to become overheated and they begin to leak.
The only remedy is to remove the scale and reroll the
tubes, but in order to remove the scale it is usually,
or at least frequently, necessary to cut out some of
the tubes.
The bagging of boilers due to the accumulation of
scale and dirt is of such common occurrence as to re-
quire no discussion, other than to say that it is the
result of improper cleaning.
Of course there are many cases in which, 'even with
the best possible care, a great deal of scale will form,
or where it is impossible to keep the boiler out of com-
mission long enough to clean it properly. But there
are also many cases in which a pretty thorough clean-
ing could be given if the engineer really wanted it
done, and realized its importance sufficiently to see
that it was done.
The number of boiler compounds which are guar-
CARE OF THE HORIZONTAL TUBULAR BOILER 139
anteed to keep boilers clean is legion, but still it will
be hard to find the one which will remove the scale
and hand it to the engineer, although this seems to be
what some men expect of it. Most of them will do all
that can be expected of them. They will soften and
loosen the scale and considerable of it will drop off.
After it is loosened the boiler cleaner should scrape
it off by entering the top and bottom with suitable
tools. Boiler compounds, like many other things,
should be mixed with a good deal of common sense, then
results will be obtained. When a boiler is badly scaled
great care must be exercised in the use of a scale solvent,
as it may cause considerable scale to drop off and bag
a sheet. The action can be watched by frequent clean-
ings and, if there seems to be danger of such trouble,
more frequent cleaning may be resorted to, or less sol-
vent may be used.
An excellent plan is to use a scale pan, which is a
shallow pan about four to six feet long and as wide as
can be passed through the manhole. It is supported
by light legs about three inches long, and is placed on
the fire-sheet directly over the grates. As the scale
falls it is caught by this pan and is thus kept off the
sheet, preventing the bagging of the latter.
OIL A SOURCE OF DIFFICULTY
Probably the most difficult thing to cope with in a
boiler is oil. There are many different kinds of oil.
Genuine crude petroleum is oil, but when properly used,
it is difficult to find anything which excels it for keeping
boilers free from scale. Kerosene is frequently used
140 BOILERS
for the same purpose, and neither causes any trouble.
The oil which we refer to, and which causes the most
trouble, is the cylinder-oil carried over by the exhaust
to an open heater or hot-well, and from thence into the
boilers. This first appears at about the water line,
and on the top tubes, where it gives no trouble, but
it soon spreads over the entire heating surface, and it
is surprising how little it takes to cause a very serious
bulge on a fire-sheet.
A bulge caused by oil is different from one caused by
scale or mud in that it usually covers considerable
area, while the latter is not often over a foot or 18 inches
in diameter, but is much deeper in proportion to its size.
When a bulge is from three to five feet long, as those
caused by oil usually are, there is nothing to be done
but to put in a new sheet. This is an expensive repair,
as it necessitates tearing down the brickwork in addi-
tion to the boiler work.
The best method of removing the oil from the feed-
water is to filter it through a bed of coke and excelsior.
This must be renewed from time to time, as it soon gets
coated with the oil and becomes useless. . There are
numerous separators on the market guaranteed to ex-
tract the oil from the steam and water, but invariably
better results have been obtained from the filter.
FAULTY BLOW-OFF PIPES
The records of a large boiler-insurance company
show that there are more claims due to the failure of
blow-off pipes than from any other single cause. A
volume might be written on this, for the blow-off pipe
CARE OF THE HORIZONTAL TUBULAR BOILER 141
certainly is a very troublesome, although necessary
evil. When the feed-water is not introduced through
the blow-off pipe, there is practically no circulation in
it, and mud and sediment are very apt to collect. If
the pipe is not protected from the direct action of the
fire, this is very liable to cause it to burn and burst.
Even though this results in no damage, it necessitates
cutting out the boiler, and this may happen at a very
inopportune time. If, however, the boiler is fed through
the blow-off, the danger of such accident is reduced
to the minimum, but even then it is better to protect
the pipe from the direct action of the flame and gases.
It is a very common practice to incase the pipe in a
sleeve formed of a pipe one or two sizes larger. This
is of no value unless the sleeve is arranged as in Fig. 75,
so as to allow a circulation of air between it and the
blow-off pipe. When the sleeve is simply slipped over
the pipe and allowed to hang loose, as in Fig. 76, it is
of no value whatever.
In order to make it effective, the sleeve should in-
close the entire pipe from the outside of the setting to
within an inch or so from the boiler, and should be held
in position by iron wedges, as shown in Fig. 75. This
allows the cool air to traverse the entire pipe, being
drawn in by the draft. While this is an excellent plan
theoretically, it is open to the very serious objection
that the sleeve rapidly burns out, and in order to
renew it, the entire blow-off pipe has to be taken down.
There is a cast-iron split sleeve made for this purpose,
which can be replaced at any time without disturbing
the pipe.
I 4 2 BOILERS
Perhaps as good a plan as any, all things considered,
is to run the blow-off pipe straight down to the bottom
of the combustion chamber and build a V-shaped
fire-brick pier in front of it, just far enough away to
allow removing the pipe and replacing it without dis-
turbing the pier.
When necessary to use fittings in the combustion
chamber, they should be of either cast steel or malleable
iron, as cast iron is too liable to crack when exposed
to high temperature.
BEST METHOD OF FEEDING A BOILER
The method of feeding boilers has had a great deal
of discussion, some advocating feeding through the
blow-off, and some as strongly advising the top feed
with a certain type of heater, the water passing through
a length of pipe in the steam space of the boiler, and
thus becoming heated to more nearly the temperature
of the water in the boiler before discharging.
It is the general opinion the top feed is, generally
speaking, the proper method; but circumstances must
necessarily determine the best method for each par-
ticular case, and the writer has seen many cases where
he has advised feeding through the blow-off. The
objection to this method is that the comparatively cool
water from the heater is discharged on the hot sheets.
The water from the heater is hot, it is true, but when
compared to that in the boiler there is considerable
difference in temperature. It is seldom that the ordi-
nary exhaust heater, except the most modern open
heaters, raises the water to more than 175 degrees,
CARE OF THE HORIZONTAL TUBULAR BOILER 143
while the temperature of the water in the boiler at 100
pounds pressure is 337 degrees. This is a difference
of 162 degrees, or about the same difference as between
boiling water and a block of ice. Now if this water is
passed through twelve or fourteen feet of pipe in the
steam space before it is discharged, its temperature
will be raised, perhaps not very much, but at the end
of this pipe it is discharged in the body of water in the
boiler, and cannot come in contact with the sheets
until it has mingled with and attained the temperature
of this water. If an injection is used, or if there is no
heater used in connection with the feed-pump, the top
feed should be used by all means.
It is fully realized that with some waters this internal
pipe soon chokes up, especially at the end, but usually
this is readily cleaned, when the boiler is cleaned, and
it may easily be made .of sufficient area to run three or
four weeks without giving any trouble.
The point of discharge for this pipe is largely a matter
of personal preference, but it should be remembered
that the sediment will collect worst at the point of
discharge. A good plan is to have the pipe enter the
front head just above the tubes and at one side of
the boiler, carrying it to within two or three feet of
the back head, and supporting it by brackets from the
braces. From here let it run across to the middle space
between the tubes, using a union near the end of this
piece. Then drop two pipes between these tubes to the
level of the lower tubes. This makes it very easy to
clean these down pipes, by opening the union and
removing them.
144 BOILERS
If there is no manhole below the tubes, so that the
scale and sediment cannot be scraped from the shell
and tubes at this point, it may be found better to dis-
charge at the side near the rear and just below the water
line.
If for any reason the blow-off pipe cannot be arranged
so that it can be properly protected from the fire (and
occasionally. this is the case), and if a good heater is
used, there is no great objection to feeding through
the blow-off if that is the preference of the engineer.
It is always well to have both systems installed so that
if one fails the other may be used.
XIII
CARE AND MANAGEMENT OF BOILERS 1
THERE has been a great deal written by different
authors on the subject of care and management of
boilers. Valuable advice has been given, yet boiler
explosions and accidents still occur. Therefore, too
much cannot be said to impress upon the mind of the
stationary engineer the importance of taking care of
boilers.
The first and most important thing to begin with is
a good, sound boiler, for if the boiler is an old and dilapi-
dated concern the best and most skilful engineer can-
not make it safe and reliable, and the only advice in
any case like this would be to have nothing to do with
it, as not only his reputation as an engineer would be
at stake but also his life and the lives of others.
When taking charge of a plant that has been run for
some time the engineer should lose no time in ascer-
taining as far as possible the exact condition of the
boilers, and at the first opportunity he should make an
internal and external examination and see that they
are free from scale and incrustation. If they are not,
he should see that they are thoroughly cleaned both
inside and outside of the shell. When a boiler is once
1 Contributed to Power by John McConnaughy.
145
146 BOILERS
thoroughly cleaned the competent engineer will always
resort to the proper means of keeping it so far as con-
ditions will allow.
The accumulation of scale can be in a measure
avoided by blowing small quantities of water from the
bottom and surface blow-off, as all minerals held in
suspension become of greater specific gravity than the
water. When heated, the tendency by specific gravity
is to settle toward the bottom while the lighter portions
remain upon the top and float in the form of a scum.
It has been found that by frequently blowing from the
surface and bottom blow-off, much of the mineral
substance which forms scale will be carried out before
it can settle sufficiently to attach itself to the iron.
By so doing, much of the trouble from scale may be
avoided.
Notwithstanding all the care that may be taken,
in some localities where the water is largely impreg-
nated with minerals a certain amount of scale will
accumulate in spite of the efforts of the most careful
and experienced engineer. There are various devices
and compounds on the market which have proved
effective and in a measure beneficial for preventing
this scale. Others are of a doubtful character; it is
advisable before using a compound to have a chemical
analysis made of the feed-water, as the nature of the
supply receives too little attention.
Some engineers having charge of boilers with man-
holes under the tubes do all their cleaning from
below the tubes and do not open the boiler on top.
As it is impossible to wash all the dirt down from the
CARE AND MANAGEMENT OF BOILERS 147
top by washing from the under side of the tubes, the
boiler is in bad condition above the tubes before they
know it and they will tell you that the boilers are in
good shape inside.
In cleaning boilers, all manholes and hand-hole
plates should be taken out and the washing should be
done from above and below the tubes. The engineer
should then go inside the boiler and clean between them,
so that any scale that has been lodged between the
tubes can be taken out. On the outside, all seam heads
and tube ends should be examined for leaks, cracks,
corrosions, pitting and grooving. The condition of
stays, braces and their fastenings should be examined.
The shell of the boiler should be thoroughly cleaned
on the outside, as soot is a bad conductor of heat, holds
dampness and is liable to cause corrosion. All valves
about the boiler should be kept clean and in good
working condition. The pumps or injectors should be
in the best working order. The connections between
the boiler and water column and also the gage glass
should receive the closest attention, but they are sadly
neglected by some engineers. The brickwork should
be kept in good condition and all air holes stopped, as
they decrease the efficiency of the boiler and are liable to
cause injury to the plates by burning.
There should be a good heater in connection with the
boiler and the feed-water as hot as you can work it, for
feeding cold water causes too much contraction and
expansion. This causes vibration in the seams and
makes them weak at those points. For example, if
one hundred pounds of steam will do your work; never
1 48 BOILERS
carry any more nor less, as the rise and fall in pressure
causes expansion and contraction of the plates.
Never open the fire doors to cool your boiler. Close
the ash-pit doors and open the smoke-box doors in
case you get too much steam, as opening the fire door
causes too much contraction by the cold air cooling
the furnace. It would be better to allow steam to
blow off from the safety valve, which will not in any
way injure the boiler.
The safety valve should be raised from its seat every
day to make sure it does not stick from any cause, and
observe from the steam gage if the valve blows off at
the pressure it is set for.
It is of the highest importance to keep the blow-off
pipe free from sediment of any kind, as the pipe is liable
to fill up and burn off, and the only way to keep it free
is to open the blow cock often enough to keep every-
thing flushed out.
The best time to blow off is in the morning before
the fires have been started up, as a good deal of sediment
in the boiler will then have settled to the bottom of
the shell and much of it will pass out when the cock is
opened. Noon is also a good time, after the fires have
been banked for half an hour or more, so that the water
in the boiler has been quiet long enough to deposit
the particles that are being whirled about with it
through all parts of the boiler.
When a blow-off cock is opened, it must be remem-
bered that it is not to be yanked wide open and then
closed the same way. This practice is very dangerous.
No valve about a steam system ought to be closed
CARE AND MANAGEMENT OF BOILERS 149
suddenly, except in time of emergency, because the
sudden strain on the pipe and fittings is liable to cause
a rupture in the pipe or else break the elbow or valve.
The boiler is the life of any plant and my advice
to all owners of steam plants is to keep a first-class
engineer, one who is strictly temperate, pay him good
wages, give him the necessary material, and his plant
will get the proper care and management.
XIV
SETTING RETURN TUBULAR BOILERS
A GREAT improvement is made when we discard the
old-time setting of return-tubular boilers, in which
cast-iron brackets were supported by brick walls which
are constantly crumbling away, for the substantial
form of setting which is obtained by suspending return-
tubular boilers from I-beams supported by cast-iron
columns.
The accompanying Figures 77 and 78 show the
setting of boilers in single or double batteries. In set-
ting an even number of boilers, as six or eight in one
setting, it is best to divide them into pairs so that
not more than two boilers will be suspended between
supports.
The principal reason for this is that when the large
sizes, such as from 150 to 250 horse-power- are used,
the size I-beam required to safely carry this load
between supports is so large that it overbalances the
cost of two or more cast-iron columns.
In setting an odd number of boilers, such as three or
five, in a battery, columns are usually placed between
each boiler with a 2-inch air space all around the column
and an air duct at the bottom of the setting which runs
through from the front to the back and connects with
SETTING RETURN TUBULAR BOILERS
BOILERS
SETTING RETURN TUBULAR BOILERS 153
each air space around the column. This keeps up
a circulation of air and the columns are kept com-
paratively cool.
In setting boilers in this manner the columns and
I-beams are set in position first. Then the boiler is
hoisted to the proper hight by means of tackle which is
fastened to the I-beams and when the boiler is brought
to the proper hight the U-bolts are slipped into place
and fastened by nuts and washers to the I-beams.
This does away with the use of blocking and barrels
which are generally used and leaves all the space clear
under the boilers.
The expansion is easily taken care of by the U-bolts
and hangers, as is shown in the setting plans, and if the
walls are properly set, they should show no cracks
as they carry no weight and are entirely free.
The accompanying table has been carefully worked
out with a factor of safety of 5 and gives the different
lengths and sizes of I-beams and columns required, so
that a person estimating on a job of this kind can
readily determine the cost of such a setting. It covers
boilers from 36 inches in diameter and 8 feet long to 90
inches and 20 feet, giving the total weight to be sup-
ported and the sizes, weights and positions of columns
and I-beams required.
154
BOILERS
SIZES AND WEIGHTS OF COLUMNS AND I-BEAMS RE
HORSE POWER
i5
20
25
3
35
40
45
50
60
Dia. of boiler in inches
36
36
42
42
44
48
50
54
54
Length of tubes in feet
8
10
10
12
12
12
13
13
15
Length of curtain sheet in
inches
ii
II
12
12
12
14
14
14
14
Total weight of boiler and
7500
10500
13300
15300
water
6500
9400
II500
14200
17800
Rear head to center of hanger
Center to center of hangers .
2-0
4~0
2-6
5-0
2-6
S~0
3-0
6-0
3-0
6-0
3-o
6-0
3-3
6-6
3-3
6-6
3-9
7-6
Front head to center of hanger
2-0
2-6
2-6
3-o
3-o
3-o
3-3
3-3
3-9
Distance between C of sup-
ports (i boiler)
6-6
6-6
7-0
7-0
7-2
7-6
7-8
8-0
8-0
Distance between C of sup-
ports (2 boilers)
1 1-8
1 1-8
12-8
12-8
13-0
13-8
14-0
14-0
14-8
Length of I-beam for i boiler .
Length of I-beam for 2 boilers .
7~3
12-6
7-3
12-6
7-10
13-8
7-10
13-8
S-o
14-0
8-4
14-8
8-6
15-0
8-10
15-10
8-10
15-10
Size of I-beam required for
one boiler
4
4
5
5
5
6
6
6
6
Size of I-beam required for 2
boilers
6
6
8
8
9
9
9
10
10
Weight per ft. of I-beam for
one boiler
7-5
7-5
9-75
9-75
9-75
12.25
12.25
12.25
12.25
Weight per ft. of I-beam for
two boilers
12.25
12.25
18
18
21
21
21
25
25
Length of cast-iron column . .
8-0
8-0
8-6
8-6
8-8
9-3
9-5
10-0
10 o
Outside Dia. of C. I. col. for
Outside Dia. of C. I. col. for
5
two boilers
5
5
5
5
5
6
6
6
6
Size of flange on ends of col
for one boiler
94
94
10
10
10
10*
io4
ro4
104
Size of flange on ends of col
for two boilers
104
104
12
12
124
124
12*
13*
134
Thickness of C. I. col. for one
boiler
4
i
i
i
\
k
4
i
\
Thickness of C. I. col. for two
boilers
1
f
i
I
\
\
f
1
\
SETTING RETURN TUBULAR BOILERS
155
QUIRED IN SETTING RETURN TUBULAR BOILERS.
70
75
80
90
100
125
ISO
175
200
200
225
225
250
60
60
60
66
66
72
72
78
78
84
84
90
90
14
15
16
i5
16
16
18
18
2O
18
20
18
20
16
16
16
i7
i?
18
18
18
18
20
20
22
22
20800
27200
35000
44000
56000
67000
75000
24800
30300
40000
48000
55ooo
65000
3-6
3-9
4-0
3-9
4-0
4-0
4-6
4-6
S-o
4-6
5-o
4-6
5-o
70
7-6
8-0
7-6
8-0
8-0
9-0
9-0
i o-o
9-0
i o-o
9-0
i o-o
3-6
3-9
4-0
3-9
4-0
4-0
4-6
4-6
5-o
4-6
5-o
4-6
5-o
9-0
9-0
9-0
9-6
9-6
10 o
10 o
10-6
10-6
n-o
II O
1 1-6
1 1-6
1 6-2
1 6-2
1 6-2
17-2
17-2
1 8-2
1 8-2
19-2
19-2
20-2
20-2
21-2
212
1 0-0
10 o
10-0
10-6
10-6
1 1 O
1 I O
11-7
11-7
12 O
I2-O
12-6
12-8
17-4
17-4
17-4
1 8-4
18-4
19-5
19-5
20-6
20-6
21-6
21-6
22-6
22-6
7
7
7
7
7
8
8
9
9
9
9
9
10
12
12
12
12
12
IS
15
IS
IS
15
15
IS
15
IS
31-5
!5
31-5
J 5
3i-5
15
40
40
42
42
60
60
60
80
80
25
80
10-8
10-8
10-8
1 1-2
I 1-2
12-0
12 O
126
12-6
13-0
13-0
13-10
13-10
5
5
5
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
8
8
8
8
8
8
8
8
i
ii*
ii*
II*
ii*
12
12
12*
12*
12*
12*
12*
13*
i4
14
14
14*
14*
IS
15
16
1 6
1 6
I?
17
i7
}
i
!
f
3
3
3
i
i
i
I
I
i
i
!
f
1
I
3
f
!
i
i
1
I
XV
RENEWING TUBES IN A TUBULAR
BOILER 1
WHILE the renewal of boiler tubes is properly the
work of the boiler maker, the engineer who knows
how to and can do it is just so much more valuable
to the employer. The purpose of this article is to de-
scribe the method employed, together with the tools
required.
First, it is essential to place a distinguishing mark
on the front and rear heads to show which tube is to
be cut out, using chalk or soapstone for the purpose,
and the best way to make sure that the helper at the
other end of the boiler marks the same tube that you
do is to run through a strip of wood four or five inches
longer than the tube. As such a strip is of use farther
along in the process it is well to make a length of J X 2-
inch pine to serve both purposes. Next, with a hammer
and a heavy cape chisel having a wide cutting edge,
which is less liable to cut or mar the boiler (see Fig. 79),
face the beads on both ends of the old tube until they
are flush with the heads of the boiler. Then, at the
front head, with a diamond-point chisel such as is shown
in Fig. 80, cut a slot or channel, T V inch wide, in the
1 Contributed to Power by J. E. Sexton.
156
RENEWING TUBES IN A TUBULAR BOILER 157
bottom of the tube, extending inward to about f of an
inch beyond the inner edge of the head, making sure
that the groove is cut in the tube only and that the head
FIG. 79.
is not cut or even marked by the chisel. Do not drive
the chisel clear through the tube, either.
With an offset chisel, Fig. 81, carefully turn up the
FIG. 80.
edges of the tube at both sides of the cut, until the
tube-end resembles the condition shown in Fig. 82,
when it will be found that this end of the tube has
FIG. 81.
been released from the head. In cutting the slot,
especially after the cutting edge of the chisel has gone
beyond the thickness of the head, if the chisel is
allowed to go through the tube it will be the source of
158
BOILERS
considerable trouble, as it will cause the tube to spread.
Hence, at this point extreme care must be used.
If a tube is corroded and muddy, it will be harder to
remove and the method will have to be changed some-
what. Considerable force is required sometimes to
remove such a tube. Instead of one slot in the bottom
of the tube, two are cut, about f of an inch apart, and
FIG. 82.
the offset chisel is used as before, except that the f-
inch piece is turned up until it looks like the letter C,
with its back toward the front of the boiler. Then pro-
ceed as before, turning the edges of the cut upward
as far as they will go. A hook on the end of a chain
or rope may then be inserted in the loop formed by
the C-piece. This takes care of the front end.
At the other end of the tube insert the end of a piece
of shafting about 10 inches long and a little smaller
in diameter than the outside diameter of the tube.
RENEWING TUBES IN A TUBULAR BOILER 159
The end of this shafting should be turned so that it will
enter the tube about one inch, with an easy fit, and by
giving a few taps on the outer end of this improvised
mandrel the tube will be loosened at this end. Then,
by working the tube backward and forward it can be
released altogether.
The next step is to mark the new tube so it can be cut
to length. Insert the Jx2-inch piece of pine into the
holes the old tube came out of until one end of the strip
extends through the rear head about ^ of an inch.
Hold it there and proceed to place a mark on the end
extending from the front head & of an inch from face
of the head. This gives the proper length to which
to cut the new tube. Then, while the tube is being cut
to length, take a half-round second-cut file, or a finish-
cut file, and carefully smooth up the heads around the
holes, removing any marks or cuts which may have
been made in taking out the old tube. This is to pre-
vent future leaks. Next, push the new tubes into place
and station the helper at the rear end with a tube
expander, being sure that the ends of the tube are equi-
distant from the heads. It is advisable to insert one
end of an 8-foot section of i-inch pipe in the front end
of the tube, for a distance of 12 inches or so, and exert
a downward pressure on the lever so provided to pre-
vent the tube from turning while the rear end is being
expanded. As soon as the tube is tight at the rear end,
proceed to expand the front end.
A self-feeding expander, Fig. 83, will give good
results, especially if a ratchet wrench is used to turn
the spindle, for one can tell by the feeling just when
i6o
BOILERS
to stop expanding. A monkey wrench will do, however,
if a ratchet wrench is not available.
The beading comes next. This requires a special
tool similar to that shown in Fig. 84. Place the long
prong of the tool inside the tube, with the short prong
pressing against the tube-end. Then bead the tube-end
FIG. 83.
thoroughly throughout the circumference, for if it is
only beaded here and there it will prove very unsatis-
factory. When both ends are beaded, use the expander
lightly in each end once more, to remove the marks
made by the beader.
If both hand-hole plates are tight and the blow-off
valve works O. K., fill the boiler with either hot or cold
water, until the tube is covered, and if the tube does
not leak water it will hold steam, and the boiler is ready
to put into commission. If the tube leaks, re-expand
it very lightly. Ordinarily, a man and helper can
renew a tube in an hour, with ease.
XVI
USE OF WOOD AS FUEL FOR STEAM
BOILERS 1
IN nearly all plants where lumber or wooden articles
are the finished products, wood is used as a fuel for the
boilers, because it is a refuse and is easily and cheaply
disposed of in that manner. In some plants the amount
of this refuse is greater than can be burned under the
boilers; in others, there is not enough waste to furnish
the steam required.
This is the case in a great many wood-working
industries, and in some sawmills on the South Atlan-
tic coast. To this class of industries this article is di-
rected.
A certain wood is a good fuel or a poor fuel, depending
on (i) the moisture contained and (2) the size of the
pieces as fired. Whether it burns well under the boiler
depends on the shape of the furnace, the method of
firing and the draft of the chimney.
CALORIFIC VALUE OF VARIOUS WOODS
The main idea to be shown in this section is that the
value of all woods is about the same, depending on the
amount of moisture contained.
1 Contributed to Power by J. A. Johnston.
161
162 BOILERS
In various works of reference, the weight of one cord
of different woods (thoroughly air-dried) is about as
follows, the quality of coal not being given :
Hickory or hard maple 4500 Ib. equals 1800 Ib.
of coal (others, 2000 Ib.).
White oak 3850 Ib. equals 1 540 Ib. of coal (others,
1715 Ib.).
Beech, red and black oak 3250 Ib. equals 1300 Ib.
of coal (others, 1450 Ib.).
Poplar, chestnut and elm 2350 Ib. equals 940 Ib.
of coal (others, 1050 Ib.).
Average pine 2000 Ib. equals 800 Ib. of coal
(others, 925 Ib.).
Referring to the figures last given in each case in
connection with "others," it is said:
" From the above it is safe to assume that 2\ pounds
of dry wood are equal to i pound of average quality soft
coal, and that the fuel value of different woods is very
nearly the same, that is, a pound of hickory is about
equal to a pound of pine, assuming both to be dry."
It is important that the woods be dry in the com-
parison, as each 10 per cent, of water or moisture
in the wood will detract about 12 per cent.- from its
fuel value.
Take an average wood of the chemical analysis:
Carbon, 51 per cent.; hydrogen, 6.5 per cent.; oxygen,
42 per cent.; ash, 0.5 per cent. If perfectly dry, its
fuel value per pound, according to Dulong's formula,
V = i4,50oC + 62,000
= Ti4,50oC
USE OF WOOD AS FUEL FOR STEAM BOILERS 163
is 8170 B.t.u. The calorific value of carbon equals
14,500 B.t.u., and the calorific value of hydrogen
equals 62,000 B.t.u.
The hydrogen in the fuel being partly in combination
with the oxygen, only that part not in such combina-
tion can be counted on as a fuel, hence the factor
(*-)
If this wood as ordinarily dried in air contains 25
per cent, moisture, then the heating value of a pound
of such wood is 8170 X 0.75 = 6127 B.t.u., less the
heat required to raise the J pound of water from atmos-
pheric temperature to steam, and to heat this steam to
chimney temperature. Say, for instance, it takes 150
B.t.u. to heat the water to 212 degrees and 966 B.t.u.
to evaporate it to steam, and 100 B.t.u. to raise the
temperature of the steam to chimney temperature;
in all 1216 B.t.u. per pound or 304 B.t.u. per J pound.
The net value of the wood as a fuel would then be 6127
- 304 =5824 B.t.u., or about 0.4 that of i pound of
carbon. This method can be applied to any wood,
knowing its chemical analysis and its percentage of
moisture as burned.
THE MOISTURE CONTENT
As nearly all woods have about the same chemical
analysis, the heat value of woods depends, as before
mentioned, almost entirely on the moisture contained
in the wood when burned. When newly felled wood
contains a proportion of moisture which varies much
164 BOILERS
in different kinds and different specimens, ranging
between 30 and 50 per cent., and averaging about 40
per cent. Perfectly dry wood contains about 50 per
cent, of carbon, the remainder consisting almost entirely
of hydrogen and oxygen in the proportion which forms
water. The coniferous (pines) family contains a small
quantity of turpentine, which is a hydrocarbon. The
proportion of ash in wood is from i to 5 per cent. The
total heat of combustion in all woods is almost exactly
the same, and is that due to the 5O-per cent, carbon.
American woods vary in percentage of ash from 0.3
to 1.2 per cent., and the heat value ranges from 6600
B.t.u. for white oak to 9883 for long-leaf pine, the fuel
value of 0.5 pound of carbon being 7272 B.t.u.
In the absence of any method of determining the
heating value of a certain wood, the following are
averages of the analyses of beech, oak, birch, poplar,
and willow:
Carbon, per cent 49-7
Hydrogen, per cent 6.06
Oxygen, per cent 41 .30
Nitrogen, per cent 1.05
Ash, per cent i .80
These can be used in the foregoing formula, and will
give an approximate value for nearly all American
woods.
A very good and fairly accurate approximation of
the amount of moisture in any particular sample can
be obtained by weighing the wood (say about 10 pounds
of it), and then placing the sample in a closed vessel
USE OF WOOD AS FUEL FOR STEAM BOILERS 165
with a small hole in it to allow the steam to escape.
Subjecting the whole to a temperature of about 220
degrees until all the moisture has been driven off,
weigh the sample again, and the percentage of moisture
in the original can be computed easily. With this per-
centage known, the subtraction for moisture present
can be made, as before shown, and an approximate
value of the sample is obtained.
Nearly all woods will give a heat value, dry, of about
8200 B.t.u. Having obtained the percentage of
moisture present, the heat value of the fuel is 8200
multiplied by (100 per cent. per cent, moisture) less
(heat required to raise water contained to evaporative
point) less (heat required to evaporate water) less
(heat required to heat steam made by this water to
chimney-gas temperature). All of the latter quantities
can be obtained from steam tables.
EASIEST METHOD FOR GETTING AT THE HEAT
VALUE
Probably the easiest and most accurate of all methods
of obtaining the heat value of a certain specimen of
wood is not to inquire into the chemical analysis, but
to take a sample of the wood just in the condition in
which it is burned, place it in a closed, air-tight vessel,
and keep it there until it is brought to a calorimeter.
This instrument should be used by one who is familiar
with its use. It will give the heat value expressed as
B.t.u. per pound, dry. The percentage of moisture
being found, the correction for moisture is made as
before.
i66 BOILERS
A case of this kind, taken from a report by the writer,
may be mentioned and calculated. The fuel was sweet
gum refuse from a veneer mill, run through a hog and
ground into chips approximately the size of a man's
little finger. The logs were brought to the mill by
rafting down a river, so the chips as fed to the boilers
were not out of the water over three-quarters of an
hour. A sample of chips was weighed wet, then dried
in a closed vessel and weighed again, giving a moisture
percentage of 47.50. A sample of the dried wood was
then ground and tested in a calorimeter, giving a heat
value of 8208 B.t.u. per pound, dry.
For every pound of the wood fired there was only
8208 X 0.525 = 4309 B.t.u. given up by the wood in
burning, for there was but i.oo 0.475 = 0.525
pounds of dry wood fired for i pound of fuel.
One pound of water requires 966 B.t.u. to evaporate
it at the pressure in the furnace. There was 0.475
pound of water in the i pound of fuel fired, so that
966 X 0.475 = 4& l B.t.u. were required.
The flue-gas temperature was 340 degrees and 340 -
212 = 128 B.t.u. required to bring the steam from
the boiling point to the chimney temperatures. The
available heat in the wood was, then, 4309 461 -
128 = 3702 B.t.u.
Probably the greatest chance of error in estimating
the value of a wood as fired is to neglect the above
calculation, because the difference between its heating
value dry and its heating value as fired is often as high
as 50 per cent., while a similar calculation for coal
would give a comparatively small difference.
USE OF WOOD AS FUEL FOR STEAM BOILERS 167
After computing by either of the methods given the
heat value of the fuel to be burned, it is easily com-
puted how much water can be evaporated per pound
of fuel, and knowing the amount of available fuel,
the power to be generated at any plant under considera-
tion may be estimated.
Referring again to the same case of wet gum chips,
this fuel was brought to the boiler house by a conveyer,
the average capacity being measured at 100 pounds
per minute, or 6000 pounds per hour brought to the
boilers.
A pound of water requiring 966 B.t.u. to evaporate
it, and each pound of the fuel having 3702 B.t.u.,
3702 + 966 = 3.83 pounds of water per i pound of
fuel, with 6000 pounds of fuel per hour, the maximum
quantity of water that could be evaporated by the
boilers at 100 per cent, efficiency would be 6000 X 3.83
= 22,980 pounds per hour.
If the boiler were 70 per cent, efficient, 22,980 X
0.70 = 16,100 pounds of water per hour evaporated
from and at 212 degrees is all that could be expected,
and as 34^ pounds of water per hour evaporated from
and at 212 degrees is the equivalent of one boiler horse-
power, the evaporation given would represent 16,100
+ 34^ = 465 boiler horse-power. Under test the
boilers gave 450 boiler horse-power.
From all that goes before, it appears that wood as a
fuel has been allowed a little too high a value, inasmuch
as it is rarely if ever fed to the boilers perfectly dry.
It is generally green, and in cases of sawmills located
on the banks of navigable streams is soaked with water.
1 68
BOILERS
USE OF WOOD AS FUEL FOR STEAM BOILERS 169
Air-drying of wood extracts about one-half of the
moisture in a year. Wood perfectly dried, and then
exposed to the air, will absorb about the same amount
of moisture that it would contain after being thoroughly
air-dried. However, when wood is to be used as a fuel,
it is almost out of the question to contemplate drying
it, so the proposition is to burn the fuel available in
the best manner.
FUEL AVAILABLE
Of course there cannot be given any even approxi-
mate method of calculating the amount of fuel that
will be available in the refuse from any contemplated
plant, for each and every one is to work under different
conditions.
In plants already built, an estimate can be made
by weighing the fuel brought to the boiler room, and
by foregoing methods determining heat value, the
available horse-power can be computed.
Most sawmills furnish enough refuse in slabs to run
the boilers required to operate the plant. Wood-
working plants, sash, blind and door manufactories,
furniture factories, etc., depend entirely on the kind
of product, as to the amount of scrap.
This will also depend largely on the plant at which
the installation is contemplated. Furniture factories,
woodworking plants, etc., generally work the kiln-
dried lumber up so closely that the refuse as it comes
to the boiler is already in an easily burnable condition,
that of sawdust, shavings, or small strips or blocks.
These can be fed directly to the furnace without further
preparation.
I yo BOILERS
In most sawmills where the slabs come off of the logs
in long pieces, it is not possible to get the fuel to burfi
easily if fed as slabs, so it is often and generally in the
sawmills on the Atlantic coast fed through a hog which
grinds the slabs into chips varying in size from a man's
three fingers to one finger or smaller.
This is undoubtedly the best way in which to intro-
duce this fuel to the boiler, for it is then easily handled
by conveyers, and can be dumped directly into the fire
without any manual work, while slabs will generally
require handling, unless some extra design is prepared
to meet the case. 1
The various forms in which wood is fed to the furnace
may be summarized as: Cordwood, shavings, sawdust,
dust from a hog, strips and blocks from a factory, and
tan-bark.
KIND OF FURNACE REQUIRED
Efficient burning of wood requires a large combustion
chamber, and grates arranged to prevent admission
of a surplus of air. This cannot be obtained to good
advantage in the usual coal-burning furnace, so the
dutch oven has been developed to meet requirements.
This is an extension of the fire-box in front of the boiler,
as shown in Fig. 86, with a firing hole in the top
through which the ground fuel or sawdust can be fed
directly from the conveyer or chute to the grate.
As wood fuel is generally wet, or contains a large
amount of moisture, the conditions of success, as
pointed out by Thurston, are: To surround the mass
so completely with heated surfaces and with burning
1 A case of this kind is mentioned in Power, November, 1907.
USE OF WOOD AS FUEL FOR STEAM BOILERS 171
1 72 BOILERS
fuel that it may be rapidly dried, and so arranging the
apparatus that thorough combustion may be then
secured, the rapidity of combustion being precisely
equal to, and never exceeding, the rapidity of drying.
If the proper rate of combustion is exceeded, the dry
portion is consumed completely, leaving an uncovered
mass of fuel which refuses to take fire.
These conditions are met in the dutch oven, because
of the fact that the fire is completely surrounded by
fire-brick walls, which become heated to a very high
temperature, especially in the case of burning pine
shavings. This condition of good burning has been so
well met in some cases that the fire-brick lining could
not withstand the high temperature longer than a
month.
The dutch oven has a firing door and an ash door
on the front; the firing door may be used to fire any
large pieces of wood, but results are best where the fire
door on the front is never opened except for cleaning.
Fig. 87 shows an arrangement where the fuel con-
sisted almost entirely of kiln-dried refuse from a wood-
working plant, coming to the boilers in short sticks
from about ^ X J X 12 inches to blocks i X 3 X 10
inches, all mixed with sawdust and shavings from
planers.
In the boiler room the floor is on an exact level
with the top of the dutch oven. The fuel is dumped
from a conveyer on this floor and shoved by hand into
the holes on top of the ovens, and as the holes are kept
full of fuel all the time, the doors over them are never
closed. The boilers are of the Heine water-tube type,
USE OF WOOD AS FUEL FOR STEAM BOILERS 173
174 BOILERS
arranged in a battery of three and each rated at 300
horse-power. This installation gives perfect satisfac-
tion.
Another form of combustion chamber, shown in Fig.
85, is very satisfactory for burning sawdust with a small
mixture of shavings. The grate must be kept covered
all the time, or too much air Will get through, thereby
decreasing the efficiency of the boiler. In this case the
fuel is fed in a constant stream from a chute and is
shoved back over the grate by a man on the firing floor.
For ordinary air-dried cordwood, a good grate is one
placed at the firing-floor level, the area of grate being
reduced to about two-fifths the amount required for
coal by sloping the furnace walls inward, beginning
just under the arch. The grate is, of course, at the
bottom, and the cordwood can be carried to a depth
of 30 to 36 inches, so that the freshly fired wood will
crowd down that which is partly burned, filling the
large interstices at the bottom with burning coals,
and preventing leakage of air past the fire.
MISCELLANEOUS POINTS
In handling any kind of wood fuel, it is better, even
in small installations, to have the fuel brought by some
carrier, as a conveyer, chute or air blast, to the furnace.
With dry wood in small pieces, as dust from a hog, or
shavings, the fuel being brought to the fire-room, one
man can care for about 300 horse-power of boilers.
If it is brought right over the firing hole to a dutch
oven by an overhead carrier, he can care for, in some
cases, 500 horse-power.
USE OF WOOD AS FUEL FOR STEAM BOILERS 175
Sawdust and dry shavings are very extensively
handled by blowers, the suction of the blower being
connected to the saw frame or planer, and the refuse
being blown into a receptacle over the boiler room.
It is then dropped by chutes directly into the fire, or
may be blown directly in by the blast furnishing air for
the fire.
A chimney could be designed from theoretical calcu-
lations involving the chemical composition of the wood
to be burned, but as a plant burning wood is rarely or
practically never run on a Weight basis, this would not
be a practical method.
It has been borne out by practice that a chimney
designed for a certain horse-power for bituminous coal
will work well for wood. The accompanying curves
were calculated from Kent's formula:
In Figs. 88 and 89, with any boiler horse-power and
any suitable hight, the area of stack can be found. In
Fig. 90 this area is expressed for round or square stacks.
176
BOILERS
J*
.fc 2
V
USE OF WOOD AS FUEL FOR STEAM BOILERS 177
1 7 8
BOILERS
a
o
__!
S 8 S S 8 8 S
XVII
BOILER RULES
THE Board of Boiler Rules appointed under a recent
act of the Massachusetts legislature has adopted the
following regulations:
SECTION i MAXIMUM PRESSURE ON BOILERS
1. The maximum pressure allowed on any steam
boiler constructed wholly of cast iron shall not be
greater than twenty-five (25) pounds to the square
inch.
2. The maximum pressure allowed on any steam
boiler the tubes of which are secured to cast-iron headers
shall not be greater than one hundred and sixty (160)
pounds per square inch.
3. The maximum pressure allowed on any steam
boiler constructed of iron or steel shells or drums shall
be calculated from the inside diameter of the outside
course, the percentage of strength of the longitudinal
joint and the minimum thickness of the shell plates;
the tensile strength of shell plates to be taken as fifty-
five thousand pounds per square inch for steel and forty-
five thousand pounds per square inch for iron, when
the tensile strength is not known.
179
i8o BOILERS
SHEARING STRENGTH OF RIVETS
4. The maximum shearing strength of rivets per
square inch of cross-sectional area to be taken as
follows :
Iron rivets in single shear 38,000 Ib.
Iron rivets in double shear 70,000 Ib.
Steel rivets in single shear 42,000 Ib.
Steel rivets in double shear 78,000 Ib.
FACTORS OF SAFETY
5. The lowest factors of safety used for steam boilers
the shells or drums of which are directly exposed to the
products of combustion, and the longitudinal joints of
which are of lap-riveted construction, shall be as
follows :
(a) Five (5) boilers not over ten years old.
(b) Five and five-tenths (5.5) for boilers over ten
and not over fifteen years old.
(c) Five and seventy-five hundredths (5.75) for
boilers over fifteen and not over twenty years old.
(d) Six (6) for boilers over twenty years' old.
(e) Five (5) on steam boilers the longitudinal joints
of which are of lap-riveted construction, and the shells
or drums of which are not directly exposed to the
products of combustion.
(/) Four and five-tenths (4.5) on steam boilers the
longitudinal joints of which are of butt and strap
construction.
BOILER RULES 181
SECTION 2
Section 2 sets forth the standard form of certificate
of annual inspection.
SECTION 3 FUSIBLE PLUGS
1. Fusible plugs, as required by section 20, chapter
465, Acts of 1907, shall be filled with pure tin.
2. The least diameter of fusible metal shall not be
less than one-half (J) inch, except for working pressures
of over one hundred and seventy-five (175) pounds gage
or when it is necessary to place a fusible plug in a tube;
in which cases the least diameter of fusible metal shall
not be less than three-eighths (f) inch.
3. The location of fusible plugs shall be as follows:
(a) In Horizontal Return-tubular Boilers In the
back head, not less than two (2) inches above the upper
row of tubes, and projecting through the sheet not
less than one (i) inch.
(b) In Horizontal Flue Boilers In the back head,
on a line with the highest part of the boiler exposed
to the products of combustion, and projecting through
the sheet not less than one (i) inch.
(c) In Locomotive Type or Star Water-tube Boilers
- In the highest part of the crown sheet, and pro-
jecting through the sheet not less than one (i) inch.
(d) In Vertical Fire-tube Boilers In an outside
tube, placed not less than one-third (J) the length of
the tube above the lower tube-sheet.
(e) In Vertical Submerged-tube Boilers In the
upper tube-sheet.
182 BOILERS
(/) In Water-tube Boilers, Horizontal Drums, Bab-
cock & Wilcox Type In the upper drum, not less
than six (6) inches above the bottom of the drum
and over the first pass of the products of combustion,
projecting through the sheet not less than one (i) inch.
(g) In Stirling Boilers, Standard Type In the
front side of the middle drum, not less than six (6)
inches above the bottom of the drum, and projecting
through the sheet not less than one (i) inch.
(h) In Stirling Boilers, Superheated Type In the
front drum, not less than six (6) inches above the
bottom of the drum, and exposed to the products of
combustion, projecting through the sheet not less than
one (i) inch.
(/) In Water-tube Boilers, Heine Type In the
front course of the drum, not less than six (6) inches
from the bottom of the drum, and projecting through
the sheet not less than one (i) inch.
(/) In Robb-Mumford Boilers, Standard Type
In the bottom of the steam and water drum, twenty-
four (24) inches from the center of the rear neck, and
projecting through the sheet not less than one (i) inch.
(k) In Water-tube Boilers, Almy Type In a tube
directly exposed to the products of combustion.
(/) In Vertical Boilers, Climax or Hazelton Type -
In a tube or center drum not less than one-half (J) the
hight of the shell, measuring from the lowest circum-
ferential seam.
(m) In Cahall Vertical Water-tube Boilers In
the inner sheet of the top drum, not less than six (6)
inches above the upper tube-sheet.
BOILER RULES 183
(n) In Scotch Marine Type Boilers In combus-
tion-chamber top, and projecting through the sheet
not less than one (i) inch.
(0) In Dry-back Scotch Type Boilers In rear
head, not less than two (2) inches above the top row
of tubes, and projecting through the sheet not less
than one (i) inch.
(p) In Economic Type Boilers In the rear head,
above the upper row of tubes.
(q) In Cast-iron Sectional Heating Boilers In
a section over and in direct contact with the products
of combustion in the primary combustion chamber.
(r) For other types and new designs, fusible plugs
shall be placed at the lowest permissible water level
in the direct path of the products of combustion, as
near the primary combustion chamber as possible.
XVIII
MECHANICAL TUBE CLEANERS
THE Hartford Inspection and Insurance Company,
in a recent issue of The Locomotive, sounds a note of
alarm anent the damage which may be inflicted upon a
boiler by the improper use of mechanically operated
tube cleaners. Coming, as it does, from so high an
authority, this warning has produced unnecessary
alarm among the present or prospective users of such
devices, and the statement that the dangers pointed out
are incident to them when improperly handled, and
that "many of them give very good results when used
judiciously and intelligently," is lost sight of in the
light of the stated fact that injury has been produced
by their use.
The first instance pointed out is one in which by the
use of a cleaner removing external scale by rapidly
rapping the internal surfaces of the tubes the latter
were stretched to an elliptical section to such an extent
that several of them collapsed when subjected to a
pressure of ninety pounds. With any of the cleaners
as now built by experienced and reputable makers
such a result could be produced only by the grossest
misuse of the tool and the most flagrant neglect of the
directions which are furnished with it. Tests made
184
MECHANICAL TUBE CLEANERS 185
by Professor Kavanaugh, of the University of Minne-
sota, with a 3J-inch cleaner prove the energy of the
blow when operating under a pressure of 90 pounds
to be .106 of a foot-pound and the number of blows
per minute 4,560. Only slight local distortion was
produced by allowing the hammer to operate continu-
ously in one spot.
It appears, therefore, that the distortion of the tubes
in the case mentioned must have been due to a very
unskilful use of a very badly designed cleaner rather
than to the fact that the tubes were thinned by use
but still serviceable. The same remarks will apply to
the cases of splitting mentioned.
Another effect is the lengthening of the tubes due
to the peening action, causing them either to sag or to
project through the head. This action might follow an
unduly protracted application of even a good cleaner,
but should no.t be caused by such application as is
necessary to remove ordinary scale. Such elongation
is liable to crack the cast-iron headers of water-tube
boilers, and the makers of at least one of the cleaners
of this type discourage for this reason its use in boilers
with headers of that material. Such headers are, how-
ever, dangerous in themselves and their use is rapidly
being discontinued. This peening effect should be
present in the mind of the operator of the cleaner, and
he should regulate the intensity and time of application
of the blows so as to avoid it, and watch carefully for
it at the tube sheets.
The unequal expansion caused by discharging the
exhaust from steam-opera ted cleaners through the tubes
l86 BOILERS
is also considered, and the use of compressed air for
running the cleaner, when available, advised. The
makers of the cleaners are alive to this condition,
recommend the use of air in preference to steam, and
recommend also that the boiler be cleaned while hot.
The conclusions arrived at in The Locomotive article
are as follows:
(i) That when power-tube cleaners are used they
should be kept in motion so that they cannot strike a
succession of blows against any one part of the tube;
(2) they should be operated by a pressure not exceeding
20 pounds, or, at the most, 30 pounds per square inch;
(3) steam should not be permitted to blow through the
tubes of a cold boiler for a sufficient time to sensibly
heat the tubes; (4) compressed air should be used to
operate tube cleaners unless the motive power is entirely
external to the tube; (5) in any case, the boiler should
be carefully watched during and after the application
of a power cleaner, especially around the ends of the
tubes and on the headers, and at the first sign of dis-
tress of any kind the use of the cleaner should be
promptly discontinued; (6) lastly, a power cleaner
should never be put in charge of any attendant save
one upon whose judgment and skill the owner of the
boiler can implicitly rely.
These conclusions commend themselves even to the
makers of the devices in question, with the exception
that they claim that a pressure of from 40 to 90 pounds
is better than the lower pressure recommended as giving
more rapid vibrations and of less amplitude, and deny
that the heating due to exhaust steam will injure a
MECHANICAL TUBE CLEANERS 187
sound tube. Signs of distress may be evidences of
weakness revealed by the cleaner, and point to reforms
or repairs rather than the discontinuance of the use
of the cleaner. The strictures apply principally to
cleaners operating by hammer action and discharging
steam through the tube, but do not amount to a con-
demnation of the type, the successful present use of
over 5,000 machines for a single maker evidencing that
injury from its use is exceptional and avoidable rather
than general and inherent.
INDEX
PAGE
Air bubbles 5
Area for escape of steam 116
to be braced in heads of horizontal tubular boilers, finding 67
Auxiliary valve 115
Average unit length 48
Bagging of boilers 138
Ball of safety valve, finding distance from fulcrum 105
of safety valve, finding weight 105
safety valve, weight 119
Beading tube-end 160
Blow back 108
-off pipe, care 148
pipes, faulty 140
Blowing off 148
Boiler appliances 123
at work, watching i
care and management 145
compounds : 138, 146
rules 179
Braces, number 31
Bracing, amount 35
heads of horizontal tubular boilers 67
horizontal return tubular boilers 30
Bridgewall, hight and form 137
Bubbles, air 5
steam 5
Bulge on fire-sheet 140
Bursting strength of boiler 17, 24, 29
Butt-joint, double-riveted double-strapped 58
189
igo INDEX
PAGE
Butt-joint, single-riveted double-strapped 57
triple- riveted double-strapped 61
Calorific value of various woods 161
Carle, N. A 70
Center of gravity, distance from fulcrum 119'
Chain riveting 53
Chimney for wood-burning furnace 175
Circle, finding area 80
Circulation in U-tube i
Cleaning boilers 138, 147
tubes 137
Combustion chamber in wood-burning furnace 170, 174
chamber, proper depth 135
Compressed air for running cleaner 186
Cooling boiler 148
Cracks in settings 134
Crushing of rivets . . .41, 44, 45, 47, 5. 5*, 55, 5 6 , S8 59. 60, 64, 71
Diagonal braces 3 1 , 35
Diagram, calculating 72
Diameter of rivets 70
of shell 70
valve 112
Disk Y-valves 125
Double butt-strap, efficiency 7 2
lap, efficiency 72
-riveted double-strapped butt-joint 58
lap-joint 49
riveting 14, 23
shearing 46
Drilled plate, strength 43
Dropped forge steel flanges 128
Dutch oven 170, 172
Factors of safety 29, 72, 1 80
INDEX 191
PAGE
Feed pipe, point of discharge 143
-water 147
Feeding boiler 142
through blow-off 142, 144
wood-burning furnace 174
Flanges 1 28
Force acting on heads 17
tensile 1 1
Front drum, action in 3, 4, 5
Fuel available 169
Fulcrum 86
Furnace for burning wood 170
Fusible plugs 181
Gage-glass valves 127
Graphical determination of boiler dimensions 70
Grate for wood-burning furnace 174
Hartford Inspection and Insurance Co 184
Heating value of woods 164, 165
Horizontal tubular boiler, care 133
Horse-power of boilers 1 20
Huddling chamber of safety valve 106
I-beams for setting return tubular boilers 153, 154
Jeter, S. F 40
Johnston, J. A 161
Joints, proportion 50
Kavanaugh, Prof 185
Kennett, M 133
Lap-joint, double-riveted 49
-joint, single-riveted 48
triple-riveted 51
IQ2 INDEX
PAGE
Lap-riveted joint with inside strap 54
joints, single 72
Leakage, cold air, through cracks in setting 134
Lever, length t x 9
of safety valve, effect 95
principle 84
safety valve 89
valve, amount of opening 115
weight . . . .' 119
Lift of valves 109, in
Lifting force of safety valve 103
Locomotive, The 184, 186
Loss, sources 134
McConnaughy, John 145
Man-head frames 1 29
Mass. Board of Boiler Rules 179
Model boiler i
Moisture content of woods 163
Moment of a weight or load 86
of lifting force of safety valve 103
Moments, measuring for 98
Mud-drum, action in 4, 5, 7
-drum, size 9
Net section , 48
section, failure 50, 51, 58, 59, 60, 61, 64
Nipples, long 8, 10
Oil 139
Opening of lever safety valve, amount 115
Peening action of cleaner 185
Pitch , 13
Plate efficiency, calculating 16
strength 28
INDEX 193
PAGE
Pop safety valve 100
valve 1 16
Position of weight to exert pressure on stem of safety valve. . . 93
Pressure against head 30
amount boiler will stand 37
at which valve blows off, finding 104
effect in lifting a valve 82
of changing 7> 9
internal 17
on boilers, maximum 179
valve to lift ball 91
per square inch 75
safe working 29
to burst a shell 24, 28
lift valve and stem 119
raise lever 119
raise valve, stem and lever 119
Priming 9
Projected area 22, 25, 26
Quadruple butt-strap-riveted joint 72
-riveted double-strapped butt-joint 64
Rear drum, action in 4
Reduction of pressure, effect 9
Refuse for fuel 169
Return tubular boilers, setting 150
Rivet efficiency 16
holes 71
resistance to crushing 41, 44
Riveted joints, strength n, 28, 40, 41
plate, possible modes of failure 41, 43
Robbins, C. G 1 20
Rupturing plate 42, 43, 45
Safety valve 75, 1 23
194 INDEX
PAGE
Safety valve, capacity 108
care I4 8
force necessary to lift 79
position 3, 9
rules 103
Scale, avoiding 146
Sediment . 4, 7, 9
Segmental area, finding 34
Segments of circles, areas 37
Separators 140
Setting return tubular boilers 150
Sexton, J. E 156
Shearing of rivets 13, 45, 48, 50, 51, 55, 56, 58, 59, 60, 61, 64
strength of rivets 13, 41, 44, 46, 47, 70, 71, 180
Sheet strength 28
Shell formula 72
Single lap-riveted joints 72
-riveted double-strapped butt-joint 57
lap-joint 48
shearing 46
Sizes and weights of columns and I-beams 154
Sleeve for blow-off pipe 141
Smith, C. Hill i
Solid plate, strength '. 43
Spacing of rivets 70, 71
Spring-loaded safety valves t 100
Square of a number, finding 114
Stack area, wood-burning furnace 175
Staggered riveting 53
Steam, amount escaping through opening 116
bubbles 5
gage 79, 127
wet, cause 6, 9
withdrawing 9
Steel frames and nozzles 130
lugs supporting boiler 131
INDEX 195
PAGE
Stem, distance from fulcrum ............................. 119
Stop valves in column connection ......................... 126
Strength, ultimate tensile ................................. 1 1
Tensile force ....................................... 1 1, 27, 28
strength ............................................ 41
of cast iron and forgings ............................ 129
of plate ........................................... 70
ultimate ................ . .......................... 1 1
Test, boiler ............................................ 3
Testing boiler plate ..................................... 41
machine ............................................. 41
Thickness of plate ...................................... 70
Through braces ...................................... 31, 35
Top feed ......................................... . ..... 142
Triangle, area .......................................... 81
Triple butt-strap, efficiency ............................... 72
lap, efficiency ........................................ 72
-riveted double-strapped butt-joint ...................... 61
lap-joint .......................................... 51
Try-cocks ............................................. 127
Tube cleaners, mechanical ............................... 184
Tubes, cleaning ........................................ 137
renewing in tubular boiler .............................. 156
U-tube, circulation ...................................... i
Ultimate tensile strength ................................. 1 1
Unit section of joint .................................... 47
United States Board of Supervising Inspectors, rules. . . .36, 108, no,
Valve area ................................. 108, no, 112, 119
auxiliary ............................................. 115
diameter ............................................. 119
lifting ............................................... 82
weight with stem ...................................... 119
196 INDEX
PACE
Waste pipe for safety valve 1 24
Water column '. 125
-tube boilers 9
Weight of valve and stem of safety valve, effect 95
to hold pressure on valve 9 2
Wet steam 6 > 9
Wood as fuel for steam boijers 161
Working pressure 7
pressure, safe - 2 9
UNIVERSITY OF CALIFORNIA
LIBRARY
This is the date on which this
book was charged out.
OCT. 21911
[30m-6,'ll]
YB 10714
196487