CALIFORNIA
AGRICULTURAL EXTENSION SERVICE

CIRCULAR 4

November, 1926

IRRIGATION BY
OVERHEAD SPRINKLING

H. A. WADSWORTH

PUBLISHED BY

THE COLLEGE OF AGRICULTURE
UNIVERSITY OF CALIFORNIA

Cooperative Extension work in Agriculture and Home Economics, College of Agriculture,
University of California, and United States Department of Agriculture cooperating. Dis-
tributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. B. H. Crocheron,
Director, California Agricultural Extension Service.

UNIVERSITY OF CALIFORNIA PRINTING OFFICE

BERKELEY, CALIFORNIA

1926

Digitized by the Internet Archive

in 2011 with funding from

University of California, Davis Libraries

http://www.archive.org/details/irrigationbyover04wads

IRRIGATION BY OVERHEAD SPRINKLING

H. A. WADSWOETHi

INTRODUCTION

Although the irrigation of truck crops by overhead sprinkling has
long been a common practice in some parts of the United States, with
some citrus fruits irrigated this way in Florida, the application of
water by overhead sprinkling has but recently become a factor in
California orchard irrigation practice. Though scattered installations
which have been in operation for some years are to be found in various
parts of the State, the majority now in operation have been established
since 1924.

Irrigation by sprinkling is an attempt to imitate rainfall. "Water
is carried in pipes under such pressure that when released from
sprinkler heads or from perforated pipes, the surface to be irrigated
is sprinkled with the coarse drops of a heavy shower. In details,
individual installations may differ widely, but in general, the prin-
ciple is the same. Certain manufacturers of sprinkling equipment
recommend distribution from horizontal pipes supported above the
surface of the ground and equipped with non-corrosive nozzles or jets
at fixed intervals along them. Such an installation can serve a zone
of a length equal to that of the pipes and of a width determined by
the available pressure and by the number of lines. Other manufac-
turers recommend rotary sprinklers. When these are used, sprinkler
heads somewhat similar in design to revolving lawn sprinklers are so
located in the area to be irrigated that the overlapping circles of
application completely cover the area.

Sprinkler equipment is relatively costly regardless of the type of
distributing system selected. Many installations which are designed
to eliminate all labor of irrigation except the opening of a valve or
the starting of a pump represent an investment up to $300 an acre.
Under favorable conditions, when the operator is willing to handle
some portable sprinkling equipment, the initial cost may be reduced
to one-half of this amount or less. When natural pressure is not
available for the operation of a sprinkler installation, pumps must be
included in the plan. In such cases the first cost of the system will
be increased by the cost of the pump with its fittings, and the annual

1 Assistant Professor of Irrigation Investigations and Practice and Assistant
Irrigation Engineer in the Experiment Station.

4 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 4

cost will be increased by the carrying charges on this additional
investment and by the cost of the power consumed.

Because of the large investment represented by sprinkler equip-
ment, the practice of overhead irrigation has been mainly limited to
the irrigation of high-value crops on high-priced land. In California,
numerous plantings of oranges, lemons, avocados, and nursery stock
are being irrigated by this method. Sprinkling is often practiced in
truck-growing areas where soil, market facilities, and climatic con-
ditions warrant the expense involved. Because of the flexibility of
the system and the possibility of irrigating small tracts efficiently
with a minimum of labor, overhead irrigation is rapidly finding favor
with poultrymen as a means of watering chicken runs and of irrigat-
ing small areas for green feed. The method is also sometimes used for
the irrigation of lawns and ornamental shrubs.

OVERHEAD SPRINKLER LINES

Sprinkler installations for the irrigation of orchards, nurseries,
and truck gardens fall into two general classes: perforated overhead
pipes, sometimes called overhead nozzle lines, and revolving sprinkler
systems which water circular areas.

The distribution of irrigation water in the form of small jets
forced through openings in the shell of the pipe was the first method
used. In these early installations a few lengths of pipe were per-
forated and the water forced through them by a simple hand force
pump. Since these perforations were not reinforced with non-cor-
rosive metal, the holes gradually became irregular in sliape or entirely
clogged.

Modern sprinkler lines carry patented nozzles of non-corrosive
material. These are screwed into tapped holes drilled through the
shell of the pipe. The holes through these nozzles are intended to be
so shaped that particles of rust, which may be carried through the
pipe, cannot clog them. It is extremely important that the nozzles in
a pipe line be set in a straight row. Special drilling machines have
been designed to facilitate this.

LOCATION AND DESIGN OF NOZZLE LINES

A strip of land 50 feet wide can be irrigated from a single over-
head line if that line be so arranged that it can be rotated through
a turning union and the angle of the jets changed. When the angle
of the jet is 45 degrees above horizontal, greatest distance is secured.
Hence, the total angle available in the turning union should be 90

1926]

IRRIGATION BY OVERHEAD SPRINKLING

degrees. Considerable attendance is required with installations of this
sort if changes in angle of jet and consequently in the area served
are made by hand. Turning machines consisting of small turbines,
driven by the flow of water in the vertical supply type, have been
devised. These attachments slowly turn the pipe line through the
required angle. Need for personal attendance is practically obviated
by the use of this device.

The details of the installations vary widely with the proposed use.
For truck crops and ornamental plantings the pipes may be carried
on short posts, or even laid on the ground. When the pipes are carried
on posts, these supports are usually about 15 feet apart. When longer
spaces are used, it becomes increasingly difficult to turn the line
because of its sag. Simple roller bearings can be secured which may
be placed on the posts as an aid to easy turning. For short lines the
bearings may be eliminated and the lines held in place by metal straps
over the tops of the posts. Even in good installations with abundant
pressure, lines longer than 700 feet are not to be recommended.

Many growers object to the obstruction to cultivation which results
from placing sprinkler lines on short posts. Posts carrying the pipe
lines about six and one-half feet above the ground permit the passage
of men and horses under the lines and eliminate most of this trouble.
Four by four inch redwood posts make suitable supports for sprinkler
lines. They should be long enough to be set in the ground 21/2 or 3
feet and should still give a 6I/2 foot clearance. When greater per-
manence is required, sections of IVi-inch or li/2-inch iron pipe set in
concrete footings may be used.

Obstruction to cultivation can be still further reduced by the use
of high poles which may be from 100 to 200 feet apart. The nozzle
line is then suspended from a wire cable which joins the tops of these
poles and hangs in the form of a catenary between them, the wires
supporting the nozzle lines carrying specially designed galvanized
iron hooks equipped with simple roller bearings at their lower ends.
The nozzle lines fit into these hooks and can be brought to the proper
height by adjustment of the wires leading from the supporting cable.

Because of unavoidable sag in the cable, the height of the poles
supporting it should be considerably greater than the height required
for the nozzle line. Suitable poles can be made from standard tele-
phone poles having a diameter of 8 to 10 inches at the base and 6 to 8
inches at the top. These poles should be set in holes at least 6 feet
deep and should be tamped firmly in place. For greater permanence,
footings of concrete may be used. Since any deflection of the high
posts from their original position would result in a further sagging

6 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 4

of the cable and a consequent distortion of the nozzle line, it is well
to anchor the end posts with guy wires fastened to ' ^ deadmen. ' ' These
"deadmen'' may be any massive concrete or wooden members buried
3 or 4 feet below the surface and attached to an anchor rod which
terminates in an eyebolt above the surface. The "deadmen" should
not be closer to the base of the pole than a distance equal to one-third
its height. Guy wires attached to these anchor rods by means of
turnbuckles give rigid support for the poles. Future sag in the line
can be corrected by the turnbuckles.

The weight of the cable to be used depends upon the spacing of
the poles, the length of the pipe line to be supported, and the pipe
sizes which make up that length. Most manufacturers who produce
sprinkling equipment of this sort maintain an engineering office where
information as to the suitable spacing of poles and the required cable
sizes can be secured. When such advice is not available, an engineer
familiar with sprinkling systems should be consulted and his advice
followed. No detailed design of sprinkler lines can be given which
would be suitable for common use, since each installation must be
considered individually before an intelligent design can be offered.
In general, the nozzle lines should be at right angles to the supply
lines and should run the long way of the area to be irrigated, in order
that obstruction to cultivation may be minimized. If the pipe sizes
making up the nozzle lines are wisely chosen, and if sufficient pressure
is available, the lines may be as far apart as 50 feet, if necessary to
secure a better location in the field.

The pipe sizes to be used for overhead sprinkling lines depend
upon the type of nozzle used, the pressure available at the intake of
the line, and the distance between nozzles.

As has been stated above, the overhead sprinkling line finds its
greatest popularity in nursery work, truck growing, and ornamental
planting. The oldest installations in California were of this type and
were the first ones used for the irrigation of citrus trees. The practice
of overhead sprinkling did not spread among citrus growers, however,
because of the obstruction offered to cultural practices by the sup-
porting posts. Horizontal lines have also proved a great inconvenience
in the handling of fumigation tents. Furthermore, it is probable that
the fine stream issuing from a nozzle of the type used on such lines
increases evaporation loss. Figure 1 shows a typical overhead sprinkler
line in operation.

^^^^] IRRIGATION BY OVERHEAD SPRINKLING

FITTINGS FOR NOZZLE LINES

In addition to the special brass nozzles which are essential to satis-
factory operation of a sprinkler installation of this sort, there are
other fittings which reduce difilculties of installation and make for
greater convenience in operation. Automatic turning equipment has
already been mentioned, as has also the simple roller-bearing saddle,
in which a long length of pipe may rest and still turn easily. The
saddle is supplied with several base fittings for use with various
methods of support for the sprinkler line. Turning unions completely

Fig. 1. — General view of overhead sprinkler line. Sprinkling from a perforated
horizontal pipe, which may be rotated through a turning union, is a popular means
of applying water to ornamental plants, vegetables, and poultry runs.

assembled are sold by manufacturers of sprinkler equipment. Ordi-
narily a perforated conical strainer is built into the union so that
water entering the nozzle line may be kept free from dirt, which might
clog the fine nozzle openings. For extensive installations where several
parallel lines are to be turned in unison, the power supplied by the
turbine of the automatic turning equipment is inadequate and
hydraulic oscillators may be obtained in that case. The reciprocating
action of the central oscillator is carried to the turning unions which
are operated by carefully balanced cables.

CALIFORNIA AGRICULTURAL EXTENSION SERVICE

[CiRC. 4

Flushing valves are usually installed at the end of each nozzle line
to permit the removal of dirt and scale from the line without the
necessity of dismantling.

Difficulty is often experienced in assembling sections of drilled
pipe since the couplings must be tight and the nozzles in the several
sections in perfect line. The use of quick-acting couplings with
squared sockets makes it impossible to assemble the pipe unless the
nozzles in the several sections are in perfect alignment.

COS

\\v

^Po//er
tiear/ng

M > Jurnina

> Turning
union

S<H

'T'^sf^jrT^^^r^-j^,

Oofe
vo/ve

K-"'i.

"P^imwn^^Tims^T

77^^^//^///

Fig. 2. — Detail of typical sprinkler line assembly. The special fittings required
for the installation of overhead sprinkler lines can be secured only from manu-
facturers of sprinkling equipment.

Other equipment such as gate valves, couplings, tees, and unions,
which may be necessary for assembly, is common to all pipe work and
need not be considered. Figure 2 shows the detail of a sprinkler line
assembly.

WATER REQUIRED FOR OPERATION

For outdoor irrigation, with nozzles spaced on 3-foot or 4-foot
centers, a supply of one gallon per minute for every 15 feet of line
should be provided. AVith uniform application over a strip 50 feel
wide, such a flow would provide an irrigation of one inch in about
eight hours.

1926] IRRIGATION BY OVERHEAD SPRINKLING

PEESSURE EEQUIREMENTS

A pressure of from 25 to 35 pounds per square inch is required at
the head of a nozzle line for satisfactory distribution. In cases where
this pressure is not available or where it cannot be created without
prohibitive cost, special nozzles should be used which are designed for
low pressure operation. Planning such a low pressure system is a
special problem which should be undertaken only under advice from
a reliable manufacturer of sprinkling equipment of this sort.

When the sprinkler lines are remote from the source of pressure,
much more pressure is required at the source than can be used at the
intake end of the nozzle line. Pressure is always consumed when
water is forced through a pipe line. This loss results in the necessity
of overcoming the resistance to flow, which is offered by the relatively
rough interior and small diameter of the supply pipe. The amount
of pressure necessary to overcome this friction varies with the amount
of water carried, the length of the line, the size of the pipe, the
material of the pipe, and its age. Methods of determining the pres-
sure consumed under given conditions will be discussed under a con-
sideration of the design of supply pipes.

REVOLVING SPRINKLER SYSTEMS

As has already been indicated, sprinkling heads cannot distribute
water over a given rectangular area as uniformly as a well operated
sprinkler line because of the overlap of the circles of application
which are necessary to insure complete coverage. With field crops,
nursery plantings, and truck crops, where the location of sprinklers
is not rather rigidly fixed by planting arrangement, part of this
objection can be obviated. When sprinkler heads can be located on
a hexagonal pattern and every head placed at an equal distance from
every other head adjacent to it, only about 15 per cent of the area
served will be within the zones of overlap, provided the spacing is
properly determined according to the spread which may be expected
from a single head. In cases where the location of the heads cannot
conform to a true hexagonal spacing because of the planting scheme —
or for some other reason — the amount of overlap must be increased
if complete coverage is provided. No real objection is offered by this
necessary overlap, since all sprinkler heads throw less water to the
extreme circumferance of the circle of coverage than is applied to the

10 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [ClRC 4

central area. The overlap tends to equalize any lack of uniformity
of application which may result from a single head.

Many commercial sprinkler heads now on the market throw water
with fair uniformity over a circle with a 60-foot diameter when a
pressure of from 15 to 18 pounds per square inch is available at the
head. With an expected diameter of coverage of 60 feet, sprinkler
heads should be located so that each head is 52 feet from its neighbors
in every direction. Such a spacing can be effected by staggering the
sprinkler heads on feed lines which are parallel and which are 45 feet
apart. This plan of installation is evidently impossible in orchards
that are planted on the rectangular system. Several plans of layout
are shown in figure 3. In this figure, plan A is a hexagonal instal-
lation for truck gardens, nurseries, or for orchards planted on the
hexagonal plan. Plans B, C, and D are superimposed upon rect-
angular orchard plantings.

LOCATION AND COST OF SPEINKLEES IN PEEMANENT PLANTINGS

In orchards set on the rectangular plan, with 24-foot spacings, a
close approximation to the ideal installation suggested above can be
reached by establishing sprinkler heads in alternate trees in alternate
rows. When such a scheme is adopted, the diameter of a single circle
of coverage must be two and one-half times the distance between
trees, if complete coverage is to be obtained with a minimum of over-
lap. Under the condition given the diameter of coverage required for
most efficient distribution is 60 feet.

Some growers object to locating heads directly over a tree. The
accumulation of excess water at the trunk of the tree, because of
unavoidable leaks in the sprinkler heads and the difficulty of handling
fumigation tents over trees equipped with sprinkling stands, are given
as criticisms of this method. Growers who disapprove of such an
arrangement sometimes install sprinklers in the centers of the tree
squares. The diameter of coverage required is the same in either case.
Some obstruction to cultivation must be caused by an installation in
which the sprinkler pipes rise from the centers of the tree squares.

Some types of sprinkler heads are designed for greater coverage
than the 60-foot diameter usually served by the more common heads.
It is difficult to use these special heads advantageously in orchards
on common spacings, because of the unavoidable overlap which must
be allowed to obtain complete coverage. If sprinkler heads are placed
in every third tree in every second row, the circle of application from
a single head must have a diameter equal to about three and one-third

1926]

IRRIGATION BY OVERHEAD SPRTNKIJNG

Fig. 3. — Typical layouts of permanent sprinkler installations,

A. A hexagonal installation reduces the overlap of circles of coverage to a
minimum. Each head is the same distance from its neighbors in every direction.
Such a method of installation is not adapted to orchards on a rectangular plant-
ing plan.

B. A common metliod of installation in rectangular plantings is to establish a
sprinkler head in every second tree in every second row. The sprinkler heads are
not equally spaced.

C. Economy in underground piping results when individual sprinklers can be
located in every second tree in every third row. The distribution is lacking in
uniformity.

D. When sprinklers of large diameters of coverage are used auxiliary sprinklers
are sometimes installed to insure complete coverage without excessive overlap.

12 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 4

times the distance between the trees. With trees planted on 24-foot
distances, for example, the diameter of application required would be
about 80 feet, and undesirable inequalities in application would
necessarily result.

Some manufacturers, particularly those who specialize in sprink-
ling devices for golf greens, offer sprinklers wdth great diameters of
coverage for orchard use. The advantage in using such heads lies
in economy in underground piping. The great disadvantage is that
undesirable inequalities of distribution must exist if the sprinkling
heads be located with respect to existing tree rows. In some instal-
lations with large-diameter heads, a dry area is allowed to remain
between the circles covered by four large sprinklers. This dry area
is covered by a small sprinkler fed from a lateral leading from the
nearest main.

TYPES OF SPRINKLEE HEADS

Sprinkler heads designed for orchard work fall into four main
classes, as follows :

(1) Solid heads carrying no moving parts. With these, water is
broken into drops by impact against a baffle plate in the top of the
head. The drops are forced through ports in the top or side of the
head by the pressure in the line. Such heads usually serve areas of
small diameter, their advantage being that they have no moving parts,
which eventually necessitate replacements, and that there is freedom
from leakage when in operation.

(2) Rotary sprinklers carrying small and simple moving parts.
These throw water over a greater distance than could be served by a
solid head. This wider distribution may be due either to the impact
of a revolving member against the jet, or to the centrifugal action
imparted by short arms. The pressure of the water in the riser
revolves the moving parts. Such heads usually have a greater capacity
than solid heads and usually cover a larger area. Some heads in this
class carry a thrust bearing, which is subject to wear. When this
wear becomes appreciable, the head leaks and the leakage runs down
the stand pipe, causing an undesirable accumulation at the base. One
manufacturer of a popular head in this class provides a simple ball-
bearing to accommodate this thrust with a minimum of wear.

(3) Long arm sprinklers depending on centrifugal force for the
distribution of water. Arms of brass or galvanized iron pipe are
screwed into specially designed heads, which screw on the riser pipes.
These heads contain thrust bearings, usually of babbit or monel metal
against brass. The arms are bent near their outer ends so that they

1926]

IRRIGATION BY OVERHEAD SPRINKLING

form a slight angle with the diameters of the heads, as indicated by
the longer sections of the arms. When water is forced through these
arms, the reaction to the issuing stream causes the heads to revolve.
Caps of special design are screwed to the ends of the arms to promote
uniform distribution. In many cases the cap of one arm carries a
round hole which throws a solid jet to the extreme circumference of

Fig. 4. — Types of sprinkler heads. Sprinkler heads should be selected after
consideration of the required diameter of coverage, the capacity of each head
under the available pressure, and the water supply.

the wetted circle. The other end sometimes carries an aperture of
such design that a fan-shaped jet is provided, which serves the inner
zones of the area. When the arms of such sprinklers are of galvanized
iron pipe, the bending to form off-set ends may result in scales of
rust w^iich may lodge in the discharge orifices and stop the head.

(4) Geared sprinklers, designed to secure greater coverage than
can be obtained by the common long arm type. This end is achieved

14 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 4

by having part of the water escape through a central jet of such
design that a large throw can be obtained. The remaining water is
sent through a rotary sprinkler head which supplies the inner zones
of the area. The rapid revolution of this rotor moves the large central
jet by means of a more or less elaborate gear train so that the whole
circumference can be served. Many sprinklers in this group are
adjustable so that varying quantities of water can be sent through the
central jet. Increasing the quantity discharged through the central
jet makes for increased application on the circumference of the circle
of coverage and a lighter application near the center. Several
sprinkler heads in common use are shown in figure 4.

UNIFOEMITY OF COVEEAGE FEOM EEVOLVING SPEINKLEES

An ideal sprinkler head should apply water uniformly over the
diameter of coverage. While this ideal cannot be reached, it has been
approximated closely by several modern sprinklers. When many
sprinklers are to be used for the irrigation of a large rectangular
area, a slight ''feathering out" in the uniformity of application near
the circumference is not a great disadvantage, since the overlap of
these circles of coverage occurs on the zones of lighter application and
tends to equalize them.

Many observations have been made in an effort to determine the
uniformity of application resulting from standard sprinkler heads of
modern design. Except for solid heads, which are not widely used in
orchard practice, all sprinkler heads are, to some extent, adjustable.
Any adjustment tends to influence the uniformity of distribution.
Light rotary heads can be adjusted by a slight constriction in one or
all of the small tubes through which water is discharged. A slight
bend in the soft metal of these tubes also affects the uniformity of
distribution.

Long arm sprinklers can be adjusted in two ways. One method
is to change the terminal orifices. Most manufacturers send long arm
sprinklers into the field with an assortment of brass outlet fittings to
be used on the ends of the arms. Changing a large holed fitting for
a small one results in increasing the application on the circumference.
Equipping both ends of the arms with such orifices in place of fitting
one end with a notched or diamond-shaped orifice results in excessive
application on the circumference and almost no application near the
center. Long arm sprinklers can also be adjusted by backing the
arms out of the head so that the angle formed by the offset in the arm

1^20] IRRIGATION BY OVERHEAD SPRINKLING 15

with the horizontal may be changed. If, however, the arms are backed
out so far that the plane described by the main part of the arm and
the offset is vertical, there can be no revolution and consequently no
distribution.

As has been mdicated, geared sprinklers can be adjusted by chang-
ing the proportion of the whole flow which passes through the central
jet. This can be done by the manipulation of a needle valve behind
the central jet, if one is provided, or by changing the brass orifice cap
which covers the jet.

Changes in the pressure under which a head is operating may
affect the uniformity of distribution resulting from that head.

For these reasons it seems unnecessary to give results obtained
from distribution tests. In most cases heads must be adjusted after
installation to accommodate minor and perhaps unintentional changes
in the head itself and to adapt the head to the pressure available at
the particular location. Tests for uniformity can be easily made in
the field. In making such a test cans of uniform cross-section are
placed at equal distances along one radius of the circle to be covered.
At the end of a given period, absolute equality of distribution is
reflected by equal depths in the several cans. Such a test should be
run for several hours before reliable conclusions can be reached. A
refinement of this method lies in catching the water in funnels estab-
lished at equal distances along a radius and collecting the drainage
water from such funnels in glass test tubes of equal diameters. Minor
inequalities of distribution are more quickly and accurately detected
by this method. A day with little or no wind should be chosen for
such tests, since a very slight breeze will result in a great distortion
from the normal coverage.

PEESSURE EEQUIREMENTS FOE EEVOLVING SPEINKLEES

Since the pressure under which a sprinkler head operates affects
its uniformity of distribution, recommendations as to suitable pres-
sures should be closely adhered to. Most solid and rotary sprinklers
operate eff'ectively under a pressure of 15 pounds per square inch at
the head. Long arm sprinklers require more pressure for successful
operation than solid heads. Geared sprinklers ordinarily require more
pressure for operation than sprinklers of any other type because of
the mechanical losses in the gear train. Large geared sprinklers, such
as are used for the irrigation of parks or golf greens, are sometimes
designed for operation under pressures as great as 100 pounds per

16 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 4

square inch. Manufacturers claim a diameter of 175 feet for the
circle of coverage of geared sprinklers under such pressures. The
pressures recommended by manufacturers are usually those required
at the heads. Gages should be installed at the top of the standpipe
and immediately beneath the thrust bearing, if the actual pressure
under which a head is operating is to be measured. If such a location
is impracticable, a gage may be installed nearer the ground. If this
is done, the reading on the gage should be reduced by as many pounds
as is represented by the height of the sprinkler above the gage, divided
by 2.31. This reduced pressure will closely approximate the pressure
at the head.

CAPACITIES OF SPRINKLER HEADS

Sprinkler heads vary widely in capacities. This is due partly to
differences in design and partly to the pressures for wdiich various
heads may be recommended to insure greatest uniformity of distri-
bution.

For heads commonly used for orchard irrigation, such as rotary
sprinklers and certain types of long arm sprinklers, a discharge
sufficient to cover the circle of coverage to a depth of one inch in four
or five hours may be considered as typical. Geared sprinklers may,
and usually do, discharge more than that indicated above. Solid
heads of various makes differ widely in discharge under operating
pressures.

Since knowledge of the amount of water discharged by a single
head is of great importance in the design of a sprinkler installation,
tests have been run on a few modern heads under varying pressures.

A solid head popular in the citrus areas of the southern states
was found to discharge 7.6 gallons per minute under a pressure of
35 pounds per square inch. Under a pressure of 20 pounds per square
inch, the discharge dropped to 5.9 gallons per minute, and 10 pounds
gave only 3.8 gallons.

Two makes of long arm sprinklers in common use in California
showed almost identical capacities for similar pressures. These heads
discharged 6.9, 5.3, and 3.8 gallons per minute when operated under
pressures of 35, 20, and 10 pounds per square inch, respectively.

As has been stated, geared sprinklers have greater capacities than
either solid heads or long arm sprinklers. One geared sprinkler used
in parks and on golf greens discharged 17.3 gallons per minute under
a pressure of 35 pounds per square inch. Under pressures of 20
pounds per square inch and 10 pounds per square inch, the discharge
was 13.4 and 9.4 gallons per minute, respectively.

1926]

IRRIGATION BY OVERHEAD SPRINKLING

When the discharge of a certain head nnder the recemmended
pressure is known, the time required for an application of one inch
of water can be readily computed by the following simple formula :

II D = diameter of the wetted area in feet, and

G.P.M. = capacity of the head in gallons per minute, then

r P M N/ 199 ^^ hours run required for an application of one
(x.r.M. X 1-- i^^]^ Qj^ ^j^g wetted zone.

This equation is based upon the assumption that evaporation losses
are negligible.

Fig. 5. — Botary sprinklers in operation. Permanent installations represent
a high first cost and are most popular in high producing areas.

TYPES OF INSTALLATIONS FOR USE WITH REVOLVING HEADS

Permanent Sprinkler Installations. — Installations which are pro-
vided with fixed riser pipes connected to underground laterals, are
sometimes called permanent sprinkler installations. Such an instal-
lation is shown in operation in figure 5. AVith this type it is possible
to irrigate an entire field or any part of it by an adjustment of the
valves which are at the intake ends of the laterals and in the indi-
vidual riser pipes. The number of sprinklers that can be carried by
a single lateral, the capacity of each head under the available pres-
sure, the topography of the area to be served, and, in some cases, the
head of water available are factors which affect the design. Since
these considerations vary widely in different areas, it is inadvisable
to copy an existing successful installation unless it is definitely known

CATJFORNIA AGRICULTURAL EXTENSION SERVICE

[CiRC. 4

that conditions are similar. Every problem of permanent sprinkler
design is a special problem which must be undertaken only after the
governing factors are known. A typical plan for a permanent instal-
lation is shown in fiefure 6.

. SuppfL/ pipe —. — : ., J 00 6.PM. at 60 /hj. pressure ^3"

+ t f <- » — ^-^ » f — » / + f + — t
t -t ■*- -f + +-'+--1-1/+- +- ■♦-,' +

+ / +
/

t » — r
+ t 1-

-f — +y -T 4

/
-h Y 1- t

* f 4-V »

f + /»

4.A-

+ '^.

+ +

f-— T f \ 4- T- F ? T ^^ =F r i-\ +

+ + +\4--f-+t + + + + +§^

■I

^ TTT T— TT T T T ¥ =T T + ^ +

4 4 '^+ + \+ -*- 4- 4 ^ 4- + -u +

/ ^

rt •-t — ^ • JL » * ■ — _L m. —

^-f-

4^'. 4 Y

■^/'.

/<«7

Fig. 6. — Typical plan for permanent installation. The pipe sizes indicated
above are suitable only for the conditions indicated and for installations in which
both main and laterals are level. The dotted lines indicate the point at whicli
1-incli pipe must change to 1^4 -inch pipe. Every installation is a special problem
and must be so considered. The circles represent coverage and indicate the
extent of overlap.

It is evident from the consideration of the location of sprinkler
heads, that laterals in the case of permanent plantings must be
installed adjacent to alternate rows in the grove, if heads giving

1^26] IRRIGATION BY OVERHEAD SPRINKLING 19

common diameters of coverage are to be used. Risers, capped by
sprinkler heads, start from tees located on the laterals below alternate
trees. A fair approximation to ideal distribution can be obtained in
this way.

Six sprinkling heads on a single lateral are commonly used with
sprinklers of ordinary capacities. A 10-acre area of usual shape
(Vs niile square) can be satisfactorily irrigated, if a main pipe line
runs through the center of the tract and if laterals branch to each side
from crosses installed on the main opposite the selected tree rows.
Each lateral on a 10-acre tract must carry six risers to insure com-
plete coverage. It is customary to consider larger areas as multiples
of such units. In such a case, the main mentioned above would become
a lateral of the larger installation, while the laterals would become
branches from laterals of the larger installation. Since available
water and available pressure can rarely be developed for the simul-
taneous operation of more than 10 acres, the multiple installations
suggested above are very rare.

One of the advantages of overhead sprinkling as a means of apply-
ing irrigation water is the flexibility of the method. Localized areas
of light soil can be irrigated frequently and lightly, while the heavier
soils can be watered heavily and more infrequently. Valves located
at the heads of laterals supplying water to heavy soils make it possible
to cut out these areas when water is required by lighter soils under
the same unit. Globe valves may be used for this purpose, although
simple cut-off valves are suitable, since the valve will usually be
entirely open or entirely closed. The valve in either case will be
below the surface of the ground, since it must be installed on the
underground lateral. It should be protected by a short length of
casing which ends at the surface of the ground or slightly above it.

It is practically impossible to select pipe sizes for a lateral with
such exactness that each riser on that lateral will be supplied with the
pressure required for best distribution. A small valve is usually
installed on each riser so that pressures may be equalized and each
sprinkler head supplied with the specified pressure. In some cases
a special fitting, carrying a valve and a strainer, is incorporated in
each riser at a convenient height. This fitting is so designed that the
strainer can be cleaned of scale accumulation and other debris in the
water without dismantling the riser assembly. Such fittings also
provide a convenient point at which the riser may be temporarily
removed if it interferes with fumigation. Figure 7 shows a riser pipe
equipped with a strainer and valve fitting.

CALIFORNIA AGRICULTURAL EXTENSION SERVICE

rClRC. 4

In other installations, a strainer is built into the head. Such a
design may entail the use of a ladder when the strainer is to be
cleaned.

Fig. 7. — Detail of permanent riser a8seml)ly. The offset fitting carries a
strainer and a valve by which inequalities of pressure can be accommodated. The
riser can be dismantled at this fitting for cleaning or replacement.

Some means of draining the pipe system should be provided.
Repairs and replacements can best be made on empty lines. In areas
where freezing weather is to be expected, lines should be drained.

1926] IRRIGATION BY OVERHEAD SPRINKLING 21

Drain plugs should be installed at the end of each lateral and at the
end of the main, if local conditions would cause an accumulation of
water at that point. Common plugs screwed into terminal couplings
provide a cheap and satisfactory means of drainage. In cases where
"the laterals run up hill from the main, the drain plug should be
installed in a tee connected by a short nipple to the discharge end of
the cut-off valve on that lateral.

The design of a satisfactory sprinkler installation is complex and
requires considerable familiarity with the principles involved in the
flow of water in pipes. Some discussion of the design of sprinkler
layouts and a friction head table for iron pipe of small diameters is
furnished in this circular as an aid to those who are removed from
the service furnished by manufacturers of sprinkling equipment.

As may be suggested from the list of materials required for a
permanent sprinkler installation, the cost of such a system is high.
Under average conditions, when tree rows are from 20 to 24 feet apart
and when sprinkler heads are located in alternate trees along these
lines, a cost of $300 an acre is not unusual. This cost is based upon
pipe prices obtained in the spring of 1925. When truck crops or
nurseries are to be irrigated and a more efficient location of sprinkler
heads is effected, this cost may be slightly reduced. Iron pipe has
the unfortunate property of an ever decreasing diameter due to the
formation of scale within the pipe. This property is apparent even
when pipes carry only the purest water. If an installation is planned
for a 20-year life, pipe sizes which will have ample capacity during
the whole period should be chosen. A layout based upon the capacities
of new pipe might be considerably cheaper than the estimate given
above. The estimate of .$300 an acre is based upon a design in which
the capacities of pipes ten years old are considered.

Portahle Sprinklers Operated from Underground Laterals. — Many
growers are prohibited from using a permanent installation because of
the high first cost or because of unwillingness to accept the high annual
overhead charge which such an installation would entail. The use of
portable stands attached by '^^-inch garden hose to outlets carefully
located on an underground distributing system provides for the con-
venience and benefits of overhead sprinkling without the high first
cost of a permanent installation.

There is no standard design for portable sprinklers. In most cases
growers build sprinkler stands from materials at hand and cap them
with purchased sprinkler heads. In some cases the riser pipe is
mounted on a light wooden platform by means of a bend elbow. Guy
wires run from the corners of the stand to the top of the riser. A tee

CALIFORNIA AGRICULTURAL EXTENSION SERVICE

[ClRC. 4

or elbow fitted with a hose-tliread adapter, allows for the connection
of a supply hose. Another common type is made entirely of pipe
sections and fittings. A %-inch pipe cross, fitted with 3-foot lengths
of %-inch pipe, furnishes the base. The riser pipe starts from a tee
connected to one arm of the cross by a short nipple. Three of the arms
from the cross are sealed by caps, while the fourth is fitted with a
hose thread-adapter which allows the entrance of water. Guy wires

4'x4' P/ofform

Fig. 8. — Detail of portable sprinkler stand. Such stands are usually home-
made except for the sprinkler head. The use of a drop elbow at the base of the
riser pipe simplifies the connection with the supply line.

are essential for all types of portable stands. Figure 8 shows a satis-
factory design for a portable sprinkler stand. Figure 9 shows such
stands in operation.

Hose lengths used to connect portable stands to underground out-
lets should be less than 50 feet long because of the great pressure losses
in such material. When the hose is in use short bends should be
avoided. Hose is at best short lived and should be carefully drained,
coiled, and stored in the shade between irrigations.

It is evident that economy in underground piping can be effected
by the use of portable sprinklers operated by hose lengths of 50 feet.

1926

IRRIGATION BY OVERHEAD SPRINKLING

Such underground laterals are ordinarily placed under every fifth
or sixth tree in the grove. The outlets are usually short risers, con-
nected to the underground lateral by means of tees, and capped by

Fig. 9. — General view of portable sprinklers in operation. The use of such
portable sprinklers reduces the first cost. Flexibility in operation can be gained
by the use of such an installation.

CALIFORNIA AGRICULTURAL EXTENSION SERVICE

[CiRC. 4

common garden faucets equipped for hose couplings. Trees shelter-
ing such outlets are often flagged in some way, to insure prompt
identification during irrigation.

Another saving resulting from the use of portable sprinklers as
compared with permanent installations is in the initial investment
in the risers and sprinkling heads. Long arm sprinklers which throw
relatively large quantities of water are ordinarily used on portable

60 O.PM.
^"A y^^ Pressure

-H'i

-£"

Fig. 10. — Suggested design for underground pipe system under assumed con-
ditions of available supply and pressure. Each sprinkler is operated from a
separate lateral. Note the economy of smaller pipe necessary in this scheme of
installation as compared with that shown in figure 11.

sprinklers. Six portable sprinklers are usually operated at once, and
only that number need to be provided for the usual 10-acre instal-
lation. Economy can be gained by designing the underground pipes
so that each lateral carries but one sprinkler, rather than by locating
all the sprinklers along one lateral and finishing the zone within
reach of that lateral before the next is begun. With the latter plan
of distribution, the first section of the lateral line must be of sufficient

1926]

IRRIGATION BY OVERHEAD SPRINKLING

size to accommodate the water supply necessary for the five sprinl^lers
below it in addition to that used by the first. A further saving results
in possible reduction in the diameter of the main supplying these
laterals, since the required capacity of the main is reduced at each
turnout. Figures 10 and 11 illustrate the saving which may be
effected by this design.

60 aPM.

\^// SO"^ Pressure

•

^5"

a"pipe^

e"p/pe^

jE^aoh spnnk/er ^/Ves

Fig. 11. — Suggested design for underground pipe system for use with portable
sprinklers when eaeli lateral must have sufficient capacity for the simultaneous
operation of six sprinklers.

Except for the drain plug required at the end of each lateral, few
fittings are needed for a sprinkler installation of this type. Valves
regulating the flow into the laterals may be eliminated; pressure
adjustment into individual sprinklers may be effected by manipulation
of the garden faucet serving the stand.

Portable installations of this type represent an investment of about
$100 an acre, including the cost of the portable sprinkling stands.
Isolated installations in which secondhand pipe has been used are
estimated by the owners to have cost even less.

26 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 4

Portable Sprinklers Operated from Portable Surface Laterals. —
A further decrease in cost can be effected by the use of portable
laterals in place of the underground laterals used in permanent instal-
lations. Such installations are neither popular nor common, since the
saving in cost by using them is, to a great extent, offset by the
increased labor cost of operation.

A main underground line of sufficient size to carry the quantity
of water required for the operation of the portable stands is laid on
the long axis of the area to be served. This line is equipped at
intervals of about 100 feet with risers capped by 2-inch hydrants fitted
for connection to 2-inch rubber hose. A short length of^ such hose
furnishes a flexible connection between the hydrant and a portable
lateral of li/2-iiich pipe, which is assembled on the surface of the
ground and which extends down the center of the zone to be served.
The sections of pipe which make up the surface lateral are fitted at
intervals of about sixty feet with 3/4-inch garden faucets. Portable
stands are connected by means of hose to these outlets in the surface
lateral, and a zone as long as the lateral and as wide as can be reached
by the length of hose used, is irrigated before the lateral is moved.
When one zone is completed, the surface lateral is taken apart, carried
to a position opposite the next riser on the main, and reassembled.

It is evident that the economy of pipe design which is possible if
each lateral carries but one sprinkler cannot be effected with instal-
lations of this type. The main must be large enough to carry the
entire flow to its end; since there is but one lateral, it must be large
enough to carry all the sprinklers.

DESIGN OF SUPPLY PIPE SYSTEMS FOR SPRINKLER
INSTALLATIONS

Because of its closely limited cross-section and the roughness of
its bore, iron pipe offers appreciable resistance to the flow of water.
The smaller the pipe the greater is the resistance ; and if the pipe size
remains the same, a greater resistance is offered to a large flow than
to a small one. The resistance to flow offered by a pipe can best be
measured by the loss in pressure which results when water is forced
through the pipe. If 100 feet of 2-inch pipe be fitted with a pressure
gage at each end, and a stream of water be forced through that pipe,
the gage at the outlet end will record less pressure than the gage at
the inlet end. This loss of pressure measures the resistance offered
by the 100 feet of 2-inch pipe to the flow of the quantity of water
which was forced through. If the pipe were 200 feet long, the differ-

1926]

IRRIGATION BY OVERHEAD SPRINKLING

ence between the gage readings would be twice as great. No simple
proportion exists between the loss in pressure and the quantity of
water.

TABLE 1

Pressure LO'SSes in Pounds peu Square Inch for 100 Feet of Common Iron
Pipe of Varying Diameters and for Varying Flows

Gallons

Pipe sizes in inches

per
minute

Va,

134

4 55
6 35
10.82
16 45

1.40
1.97
3.38
5.06
7.10
9.52
12 10

0.36
0.52
0.69
0.89
1.86
2.47
3.16
3.94
4.80
7.18
10 16

0.41
0.62
0.87
1.16
1.47
1.83
2.25
3.38
4.75
6.36
8.13
10 00

0.22
0.31
0.41
0.52
0.64
0.78
1 18
1.66
2.21
2.85
3.55
4.29
6 02
7.96
10 25

0.14
0.18
0.22
0.26

40
0.56
0.74
0.95
1.19

1 43
2.01
2.68
3.42

4 25

5 51
7.28
9.68

18 . .

0.10
0.16
0.23
0.31
0.39
0.50
0.60
0.85
1 11
1.42
1.76
2.15
3.06
3.98

5 10

6 40
7.70
9 20

14
17
0.22
0.26
38
0.48
0.63
0.78
0.96
1.34
1.82
2 27
2.72
3.33
4 15
5.02
5.78
6 54
7.70
9.70

0.15
0.20
27
0.35
0.43
0.53
0.74
0.99
1.26
1.56
1.91
2.25
2.68
3.12

3 55

4 03
5.59
6 91
8.58

10 40

0.09
0.12
0.15
0.18
0.25
0.33
0.42
0.53
0.64
0.76
0.90
1.04
1.20

1 36
1.81
2.34

2 90

3 51

100

120

0.10
13
0.17
20
24
0.39
36
41
47
55
73

1 09
1 37

140

160

180

200

0.12

220

240

260

280

0.23

300

350

0.35

400

450

500

Table 1 is computed from results of experiments compiled by Williams and Hazen (Williams,
Gardner, S., and Allen Hazen. Hydraulic tables. 3rd ed., revised, )/5 p. John Wiley and Sons, Inc.,
New York).

A value of 100 has been chosen for the "C" used in the computations indicated in the table above.
The use of this value results in an indicated friction loss equivalent to the loss in ordinary iron pipe
which has been in service for 10 years. Galvanized iron pipe probably deteriorates less rapidly than
common iron pipe. The friction losses, as given in table 1, are probably greater than would be expected
in galvanized iron pipe 10 years in service.

Many engineers have endeavored to determine the pressure losses
resulting when certain sizes of pipe are used to convey varying
quantities of water. Tables have been prepared from numerous
experiments by which it is possible to foretell with some degree of
exactness what losses in pressure may be anticipated under given

28 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 4

conditions of diameter of pipe, length of pipes, and quantity of water.
Table 1 shows the pressure consumed by 100 feet of common iron
pipe of varying sizes when varying quantities of water, measured in
gallons per minute, are discharged. The loss resulting from other
lengths can be obtained by multiplying the loss as given for 100 feet
by the length of the line in question, divided by 100.

The use of table 1 makes it possible to compute the pressure
required to force any flow of water through a line of any length and
diameter. For instance, if a flow of 60 gallons per minute is to be
forced through a 2-inch line 300 feet long, a pressure of 18.06 pounds
per square inch would be consumed in overcoming the resistance to
flow offered by such conditions. If the water is to be delivered at the
outlet under a pressure of 20 pounds per square inch, an initial
pressure of 38.06 pounds per square inch would be necessary.

In designing sprinkler layouts, the problem becomes more com-
plicated, for in the main pipe line the quantity is being constantly
decreased as the laterals are reached. And in the laterals, the flow
is being constantly reduced as successive sprinkler heads are supplied.
The pipe connecting the last two sprinkler heads on a lateral should
be only large enough to carry the quantity required for a single head.
The section between the main and the first sprinkler must carry the
whole flow necessary for the lateral.

There is no short cut toward the intelligent design of such instal-
lation. Each lateral must be considered in turn, usually starting with
the one most distantly removed from the source of water and pressure.
Pipe sizes are determined for each section between successive sprinkler
heads. If a manufacturer recommends, for the sprinkler head made
by him, a working pressure of 15 pounds per square inch then the pres-
sure at the foot of the stand must be enough in excess of 15 pounds per
square inch to lift the water to the top of the stand and deliver it at
the required pressure. One pound per square inch represents the
pressure exerted by a column of water 2.31 feet high. If a stand is
12 feet high, the pressure at the base of the stand must exceed the
required pressure for the operation of the head by 12 divided by 2.31,
or 5.2 pounds per square inch. A pressure of 20.2 pounds per square
inch, as measured on a gage at the foot of the stand, would be required
before satisfactory operation could be secured.

The pipe joining this last stand in the example given above with
the one next to it must be large enough to deliver the quantity of
water required by a single head through the length of pipe repre-
sented by the distance separating the stands, and must provide a
pressure of 20.2 pounds per square inch at the end of the line. The

1926] IRRIGATION BY OVERHEAD SPRINKLING 29

next section must be similarly determined. In this case, the quantity
required for two heads must be considered, since the last head and
the next to the last must be supplied.

The pipe section leading from the main to the first sprinkler on a
line must be laro^e enough to deliver the entire flow for the lateral. The
pressure requirement at the intake of this lateral must be smaller than
that which is available at the source, since there is necessarily some
loss of pressure in the main connecting the source of water with the
head of the lateral.

Table 2 has been prepared as an aid in the determinations indi-
cated above. Certain hypothetical conditions of pressure requirements
and capacities of sprinkler heads have been assumed and possible
combinations of pipe sizes computed. The pressure required at the
intake of laterals made up of the indicated pipe lengths and carrying
a certain number of sprinkler heads is also given under the heading
''Initial Pressure."

Table 2 can be used only as a rough guide to required pipe sizes,
and then only if the distance between sprinklers and the capacities
and pressure requirements are as given.

A main designed to supply sufficient pressure for the most remote
lateral is usually large enough to supply sufficient pressure for nearer
ones. Ordinarily smaller pipe sizes can be used in laterals close to
the source than in those more distant. Effort spent in a close deter-
mination of pipe sizes, so that every pound of available pressure is
utilized, is repaid by a smoothly operating system and low first cost.

The design of a system for the use of portable stands is less com-
plicated than that for a permanent installation. However, the same
principles apply and the same care should be used. The greatest
saving can be gained through the careful design of the main line, since
small reductions in diameters of large sizes are reflected in relatively
large reduction in costs per foot of pipe. The principles involved in
designing the underground distributing main are, of course, common
to all types of sprinkling installations.

DEVELOPMENT OF PRESSURE FOR SPRINKLER OPERATION

In some limited areas irrigation water is delivered through pipe
lines under such natural pressure that sprinkler installations can be
operated without the use of pumps. Such conditions, however, are
not often found. Growers receiving water from gravity ditches or
low pressure pipe lines, and those who secure water from private
wells must use pumps to supply the pressure necessary for sprinkler

CALIFORNIA AGRICULTURAL EXTENSION SERVICE

[CiRC. 4

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1926] IRRIGATION BY OVERHEAD SPRINKLING 31

operation. The cost of pumps, in such cases, must be charged against
the sprinkler installation, and the annual operation cost, including
interest and depreciation, charged against the maintenance of the
system.

When a pump is required one of the high pressure types should be
chosen, since the pressure at the intake must be sufficient to overcome
frictional resistance in the system in addition to the pressure required
for the operation of the sprinkler outlets. Two types of pumps are
in common use for this purpose, viz., displacement, or plunger, and
centrifugal pumps.

Displacement pumps are those which force water by means of a
piston or plunger traveling backward and forward in a close-fitting
cylinder. ■ Such pumps are divided into several classes, depending
upon the number of cylinders built into a single pump and upon the
action of the cylinders. A single acting plunger forces water only on
one stroke of the piston ; a double acting plunger forces water during
both the forward and the backward stroke. All displacement pumps
should be equipped with ample air chambers to act as cushions for
absorbing pulsations due to the action of the pistons. A relief valve
or by-pass should be placed in the discharge pipe to prevent damage
to the pump or motor, should the discharge be shut off during the
operation of the pump.

Displacement pumps for sprinkler operation should be chosen only
upon recommendation by reliable manufacturers of pumping machin-
ery. For certain conditions, such as an extremely high lift and
delivery at high pressures, displacement pumps are well suited. Dis-
placement pumps cannot be used wdth waters carrying sand.

Centrifugal pumps are rapidly gaining favor as sources of pres-
sure for sprinkler operation. When such a pump is used, the outlets
can be completely closed during the operation of the pump without
damage. Centrifugal pumps create pressure by forcing water into a
line by means of an impeller or vaned wheel which revolves at a high
speed in a closed shell or case. A single-stage centrifugal pump, that
is, a pump which carries but one impeller, may be used for instal-
lations where the required pressure at the intake need not exceed
50 pounds per square inch. In cases where a greater initial pressure
is required, a two-stage pump may be used. A two-stage pump con-
tains two impellers, each operating in a separate shell but rotated by
the same shaft.

Centrifugal pumps must be installed close to the source of water.
Long suction pipes should be avoided whenever possible. In cases
where a centrifugal pump must be placed directly over a water

CALIFORNIA AGRIOULTURAL EXTENSION SERVICE

[CiRC. 4

supply, as in a well, the distance from the water level during the
period of greatest draw-down, to the center line of the pump must not
exceed 22 feet. All centrifugal pumps must be primed before start-
ing. This can best be accomplished by filling the suction pipe and
pump shell by means of a priming pump located at the highest point
on the pump's shell. Figure 12 shows a direct connected single-stage
centrifugal pump used for the development of pressure for sprinkler
operation.

Fig. 12. — A typical pumping plant for sprinkler operation. Such pumping
plants are necessary when the water supply is not under pressure or when available
pressure is inadequate.

Centrifugal pumps are simple in design. They are inexpensive in
first cost, as compared with displacement pumps of the same capaci-
ties. They have few^ wearing parts and are usually equipped with
adequate oiling facilities. The better pumps are so assembled that
replacements may easily be made.

The selection of the proper type of centrifugal pump and the
proper size for a particular installation demands expert advice. The
efficiency to be gained by a centrifugal pump under any set of con-
ditions depends greatly upon the speed at which it is operated.
Recommendations with regard to the speed of operation should be
carefully observed.

1926] IRRIGATION BY OVERHEAD SPRINKLING 33

POWER REQUIREMENTS FOR SPRINKLER OPERATION

The power required by any pumping- plant depends upon the
quantity of water lifted in a given time, the height to which it must
be lifted, or the pressure required at the discharge, and the efficiency
of the plant.

A simple formula for determining the horsepower required for
lifting certain quantities of water to given heights is :

G.P.M X g X 100 ..

3960 XJ^ ^^

where G.P.M. = quantity of water lifted in gallons per minute.
H == vertical lift effected, in feet.

E = expected combined efficiency of pump and motor.
(About 65 per cent for well designed centrifugal
plants driven by electric motors.)
HP. = horsepower required.

Since causing a stream of water to flow under a pressure of one
pound per square inch requires as much power as would be expended
in lifting the same stream to a height of 2.31 feet, the equation may
also be written :

G.PJL X f X 100 ,„.

^■^■~ 1714 X E ^^>

where P = pressure in pounds per square inch which must be

effected at the discharge end of the pump.

In cases where the same pump is used to lift water through
appreciable distances, as from a well, and to subject the discharge to
a pressure sufficient to operate a sprinkler system, the motor must be
large enough to satisfy both these demands for power. Such compu-
tations can best be made by changing the pressure requirements into
the equivalent feet of vertical lift (by multiplying by 2.31) and adding
the vertical lift to the point to which pressure requirements are com-
puted. The relation stated in equation (1) can then be used. In
cases where a long suction pipe is necessary, allowances should be
made for losses in efficiency due to the resistance to flow in the suction
pipe.

34 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CiRC. 4

THE EFFECTIVENESS OF IRRIGATION BY SPRINKLING

PENETEATION AND SOIL MOISTUEE CONSIDERATIONS

The value of overhead sprinkling as a means of irrigation depends
upon the effectiveness of this method in creating and maintaining
a satisfactory soil moisture content. Soils vary in water holding
capacity and permeability, fine-textured soils holding more moisture
than coarser soils but '' taking" water less readily. Plants suffer for
water when the moisture content within the rooting zone drops below
a point known as the wilting coefficient. The wilting coefficient for
most soils may be determined in the laboratory with a fair degree of
accuracy. If it can be assumed that the major concentration of feed-
ing roots occurs in a definite soil stratum, a satisfactory^ method of
irrigation would permit the application of water by such a means
and in such an amount that the soil moisture content in* that stratum
of soil may be maintained between these limits.

Six sprinkled citrus groves in Los Angeles and Orange counties
were sampled intensively for depth of penetration of irrigation water
and soil moisture content during the irrigation season of 1925 to
determine the effectiveness of irrigation by the sprinkling method.
Three of these groves were on decomposed granite soils of low water
holding capacity and easy permeability, while three were on soils of
finer texture into which water penetrates less readily. In most cases
the groves were sampled immediately before and after each irrigation.
In every case samples were taken from the same limited areas at each
time of sampling. Although this method of sampling did not neces-
sarily indicate the average moisture content in the entire grove at the
time of the sampling, it did give a fairly accurate idea of the soil
moisture history in the small plots under consideration.

In the case of the three groves on decomposed granite soils, the
sampling indicated that satisfactory irrigations had been accom-
plished. In none of these groves did the soil moisture content in the
principal rooting zone fall below the wilting coefficient between March
and November. Adequate penetration of moisture at each irrigation
was, in most cases, indicated by an increase in soil moisture content
in the fourth foot of soil. The effect of irrigation was sometimes
evident in the fifth and sixth foot. It is to be noted that these groves
were managed by men experienced in sprinkler operation. Sprinkler
heads were well adapted to conditions, and factors determining the
required period of operation were well understood. A great measure

1926] IRRIGATION BY OVERHEAD SPRINKLING 35

of the success of overhead sprinkling in these groves can probably be
attributed to the experience of the operators.

Inadequate penetration of irrigation water was noted in each of
the three sampled groves on the heavier soil. In most cases irrigation
resulted in an increase in the moisture content of the surface foot
alone, the greater depths being at, or dangerously near, the wilting
coefficient when the residual soil moisture from winter rains had been
depleted by plant withdrawals. In one case, however, sprinklers were
operated for a period four times as long as usual and an increase in
the soil moisture content was noted to a depth of six feet. This fact
together with scattered observations upon the penetration secured in
difficult soils by overhead sprinklers in other areas seems to indicate
that adequate penetration in such soils can be obtained with experi-
ence, patience, and proper care in the selection and use of equipment.

DUTY OF WATEE

Observations on the amount of water used per acre in the irri-
gation of citrus trees by overhead sprinkling as compared with the
amount used by other methods show no significant difference which
can be attributed to the method of application. These observations
were localized in three areas. In these areas the amount of water used
in 1925 on groves under good sprinkler management were compared
with neighboring groves of comparable age, variety, and thrift, which
were irrigated by means of furrows. The results of these observations
are summarized in table 3. Although it is impossible to draw con-
clusions from such a small number of fields, it is probable that in
practice, such factors as the cost of water used, the skill of the
irrigator — and in the case of surface irrigation, the preparation of
the land — are of more importance in determining the amount of
w^ater to be used per acre than is the method of application.

EVAPOEATION LOSSES

Losses by evaporation from overhead sprinkling, especially during
periods of high temperatures and low humidity, are doubtlessly
significant in areas where water costs are high. As yet, no workable
means of measuring this loss has been devised. Irrigating by
sprinklers at night seems to reduce the losses from evaporation.

CALIFORNIA AGRICULTURAL EXTENSION SERVICE

[CiRC. 4

TABLE 3

Duty of Water in Acre-Feet per Acre on Sprinkled and Furroay Irrigated
Orange Groves, Season 1925

Area

Soil type

h
■11

II
I-

I >

n
II

.Hfe

1
Weighted
average

Sunnyslope .

Hanford gravelly
sandy loam.

8.5

1.13

1 13

1
2
3
4
5
6

4 5
4 5
4 5
10.0
10
10

1.14
1 54
1 75
1.92
1 64
1 71

1.67

Sierra Madre

Hanford gravelly
sandy loam.

1
2
3

8.7

23.0

1 88
1 26
1 05

1.28

1
2
3

5.50
4 00
3,90

1.42
1,31
1.40

1.38

La Canada

Hanford gravelly
sandy loam.

8.5

1.11

10.0

1.00

1 00

FERTILIZER DISTRIBUTION

Although conclusive experimental work is lacking, it can probably
be assumed that the distribution of fertilizing materials through the
soil after a surface application may be accomplished more speedily
and more effectively by sprinkling immediately after the distribution
of fertilizer than by any other means except a natural rain of proper
intensity and duration.

PEST AND DISEASE CONTROL

Experimental evidence as to effectiveness of overhead sprinkling
upon pest and disease control is not available.

TEMPERATURE AMELIORATION

In areas affected by hot dry winds, relief from excessive drying
out can probably be attained by sprinkling during the hours of
greatest danger, since exaporating water absorbs heat. An additional
benefit would accrue from the increased humidity in the area under
the sprinklers. In areas endangered by low temperatures, sprinkling
as a means of frost protection is of doubtful value. In freezes of long
duration, the ice load carried by delicate trees, when sprinkling is
unwisely attempted, may, and often does, cause damage to the trees.

1926] IRRIGATION BY OVERHEAD SPRINKLING 37

FEUIT QUALITY

Experienced packing house managers claim that fruit of a higher
quality comes from sprinkled groves than from groves irrigated by
other means. It has never been proved, however, that the increased
quality is due to the method of irrigation.

SUMMARY

1. Irrigation by overhead sprinkling is costly. At present this
method of irrigating is limited to the production of high-priced crops
on land of high value.

2. Intensive soil-moisture sampling during the irrigation season
of 1925 indicated that adequate soil-moisture penetration can be
secured by the sprinkling of decomposed granite and sandy loam soils
if the sprinkling equipment is w^isely selected and intelligently
operated. Experimental evidence as to the adaptability of sprinkling
to heavy soils is not as conclusive.

3. The type of installation to be adopted for a particular location
depends upon the crops to be irrigated, the money available for
investment in such equipment, and the labor available during the
irrigation.

4. The detailed design of a sprinkler layout requires considerable
skill and care.

5. Except in favored localities where natural pressure is available,
pumps must be installed to create pressure for the operation of the
system.

6. Sprinkler systems, if used, should be, installed because of their
ability to distribute irrigation water uniformly and effectively, and
not because of claims for other advantages.

7. Judgment and care are essential in the intelligent operation of
a sprinkler system. There is no substitute for a soil auger in deter-
mining the effectiveness of an irrigation.

PUBLICATIONS AVAILABLE FOE FREE DISTRIBUTION

BULLETINS

No. No.

253. Irrigation and Soil Conditions in the 366.

Sierra Nevada Foothills, California.
2G1. Melaxuma of the Walnut, "Juglans 367.

regia."

262. Citrus Diseases of Florida and Cuba 368.

Compared with Those of California.

263. Size Grades for Ripe Olives. 369.
268. Grovring and Grafting Olive Seedlings.

273. Preliminary Report on Kearney Vine- 370.

yard Experimental Drain. 371.

275. The Cultivation of Belladonna in

California. 372.

276. The Pomegranate.

277. Sudan Grass. 373.

278. Grain Sorghums. 374.

279. Irrigation of Rice in California.
283. The Olive Insects of California.

294. Bean Culture in California. 375.

304. A Study of the Effects of Freezes on

Citrus in California. 376.

310. Plum Pollination.

312. Mariout Barley. 377.

813. Pruning Young Deciduous Fruit 379.

Trees. 380.

319. Caprifigs and Caprification.

324. Storage of Perishable Fruit at Freez- 381.

ing Temperatures.

325. Rice Irrigation Measurements and 382.

Experiments in Sacramento Valley,
1914-1919. 383.

328. Prune Growing in California.

331. Phylloxera-Resistant Stocks. 385.

335. Cocoanut Meal as a Feed for Dairy 386.

Cows and Other Livestock.

339. The Relative Cost of Making Logs 387.

from Small and Large Timber. 388.

340. Control of the Pocket Gopher in

California. 389.

343. Cheese Pests and Their Control. 390.

344. Cold Storage as an Aid to the Mar-

keting of Plums. 391.

346. Almond Pollination.

347. The Control of Red Spiders in Decid- 392.

uous Orchards. 393.

348. Pruning Young Olive Trees. 394.

349. A Study of Sidedraft and Tractor

Hitches. 395.

350. Agriculture in Cut-over Redwood 396.

Lands.

352. Further Experiments in Plum Pollina- 397.

tion.

353. Bovine Infectious Abortion. 398.

354. Results of Rice Experiments in 1922. 399.

357. A Self-mixing Dusting Machine for

Applying Dry Insecticides and
Fungicides. 400.

358. Black Measles, Water Berries, and 401.

Related Vine Troubles.

361. Preliminary Yield Tables for Second 402.

Growth Redwood. 403,

362. Dust and the Tractor Engine. 404

363. The Pruning of Citrus Trees in Cali- 405!

fornia. 495

364. Fungicidal Dusts for the Control of

Bunt.

365. Avocado Culture in California.

Turkish Tobacco Culture, Curing and
Marketing.

Methods of Harvesting and Irrigation
in Relation of Mouldy Walnuts.

Bacterial Decomposition of Olives dur-
ing Pickling.

Comparison of Woods for Butter
Boxes.

Browning of Yellow Newtown Apples.

The Relative Cost of Yarding Small
and Large Timber.

The Cost of Producing Market Milk and
Butterfat on 246 California Dairies.

Pear Pollination.

A Survey of Orchard Practices in the
Citrus Industry of Southern Cali-
fornia.

Results of Rice Experiments at Cor-
tena, 1923.

Sun-Drying and Dehydration of Wal-
nuts.

The Cold Storage of Pears.

Walnut Culture in California.

Growth of Eucalyptus in California
Plantations.

Growing and Handling Asparagus
Crowns.

Pumping for Drainage in the San
Joaquin Valley, California.

Monilia Blossom Blight (Brown Rot)
of Apricot.

Pollination of the Sweet Cherry.

Pruning Bearing Deciduous Fruit
Trees.

Fig Smut.

The Principles and Practice of Sun-
drying Fruit.

Berseem or Egyptian Clover.

Harvesting and Packing Grapes in
California.

Machines for Coating Seed Wheat with
Copper Carbonate Dust.

Fruit Juice Concentrates.

Crop Sequences at Davis.

Cereal Hay Production in California.
Feeding Trials with Cereal Hay.

Bark Diseases of Citrus Trees.

The Mat Bean (Phaseolus aconilifo-
lius).

Manufacture of Roquefort Type Cheese
from Goat's Milk.

Orchard Heating in California.

The Blackberry Mite, the Cause of
Redberry Disease of the Himalaya
Blackberry, and its Control.

The Utilization of Surplus Plums.

Cost of Work Horses on California
Farms.

The Codling Moth in Walnuts.

Farm-Accounting Associations.

The Dehydration of Prunes.

Citrus Culture in Central California.

Stationary Spray Plants in California.

No.

87. Alfalfa.
117. The Selection and Cost of a Small

Pumping Plant.
127. House Fumigation.
129. The Control of Citrus Insects.
136. MeUlotus indica as a Green-Manure

Crop for California.
144. Oidium or Powdery Mildew of the

Vine.

CIRCULARS
No.

157. Control of the Pear Scab.

Lettuce Growing in California.
Small Fruit Culture in California.
The County Farm Bureau.
170. Fertilizing California Soils for the

1918 Crop.
173. The Construction of the Wood-Hoop

Silo.
178. The Packing of Apples in California.

160
164
166

CIRCULARS— (Conhnw^d)

No.

179. Factors of Importance in Producing

Milk of Low Bacterial Count.
190. Agriculture Clubs in California.
199. Onion Growing in California.

202. County Organizations for Rural Fire

Control.

203. Peat as a Manure Substitute.

209. The Function of the Farm Bureau.

210. Suggestions to the Settler in California.
212. Salvaging Rain-Damaged Prunes.
215. Feeding Dairy Cows in California.
217. Methods for Marketing Vegetables in

California.
220. Unfermented Fruit Juices.
228. Vineyard Irrigation in Arid Climates.

230. Testing Milk, Cream, and Skim Milk

for Butterfat.

231. The Home Vineyard.

232. Harvesting and Handling California

Cherries for Eastern Shipment.

234. Winter Injury to Young Walnut Trees

during 1921-22.

235. Soil Analysis and Soil and Plant

Inter-relations.

236. The Common Hawks and Owls of

California from the Standpoint of
the Rancher.

237. Directions for the Tanning and Dress-

ing of Furs.

238. The Apricot in California.

239. Harvesting and Handling Apricots

and Plums for Eastern Shipment.

240. Harvesting and Handling Pears for

Eastern Shipment.

241. Harvesting and Handling Peaches for

Eastern Shipment.

243. Marmalade Juice and Jelly Juice from

Citrus Fruits.

244. Central Wire Bracing for Fruit Trees.

245. Vine Pruning Systems.

247. Colonization and Rural Development.

248. Some Common Errors in Vine Prun-

ing and Their Remedies.

249. Replacing Missing Vines.

250. Measurement of Irrigation Water on

the Farm.

252. Supports for Vines.

253. Vineyard Plans.

254. The Use of Artificial Light to Increase

Winter Egg Production.

255. Leguminous Plants as Organic Fertil-

izer in California Agriculture.

256. The Control of Wild Morning Glory.

257. The Small-Seeded Horse Bean.

258. Thinning Deciduous Fruits.

259. Pear By-products.

261. Sewing Grain Sacks.

262. Cabbage Growing in California.

263. Tomato Production in California.

264. Preliminary Essentials to Bovine

Tuberculosis Control.

No.

265. Plant Disease and Pest Control.

266. Analyzing the Citrus Orchard by

Means of Simple Tree Records.

267. The Tendency of Tractors to Rise in

Front; Causes and Remedies.

269. An Orchard Brush Burner.

270. A Farm Septic Tank.

272. California Farm Tenancy and Methods

of Leasing.

273. Saving the Gophered Citrus Tree.

274. Fusarium Wilt of Tomato and its Con-

trol by Means of Resistant Varieties.

276. Home Canning.

277. Head, Cane, and Cordon Pruning of

Vines.

278. Olive Pickling in Mediterranean Coun-

tries.

279. The Preparation and Refining of Olive

Oil in Southern Europe.

281. The Results of a Survey to Determine

the Cost of Producing Beef in Cali-
fornia.

282. Prevention of Insect Attack on Stored

Grain.

283. Fertilizing Citrus Trees in California.

284. The Almond in California.

285. Sweet Potato Production in California.

286. Milk Houses for California Dairies.

287. Potato Production in California.

288. Phylloxera Resistant Vineyards.

289. Oak Fungus in Orchard Trees.

290. The Tangier Pea.

291. Blackhead and Other Causes of Loss

of Turkeys in California.

292. Alkali Soils.

293. The Basis of Grape Standardization.

294. Propagation of Deciduous Fruits.

295. The Growing and Handling of Head

Lettuce in California.

296. Control of the California Ground

Squirrel.

298. The Possibilities and Limitations of

Cooperative Marketing.

299. Poultry Breeding Records.

300. Coccidiosis of Chickens.

301. Buckeye Poisoning of the Honey Bee.

302. The Sugar Beet in California.

303. A Promising Remedy for Black Measles

of the Vine.

304. Drainage on the Farm.

305. Liming the Soil.

306. A General Purpose Soil Auger and its

Use on the Farm.

307. American Foulbrood and its Control.

The publications listed above may be had by addressing

College of Agriculture,

University of California,

Berkeley, California.

12to-11,'26