UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION CIRCULAR NO. 117 Bewritten February, 1923 THE SELECTION AND COST OF A SMALL PUMPING PLANT* BY B. A. ETCHEVEEEY and S. T. HAKDINGt Pumping plants have become an important factor in the irrigation development of California. The U. S. Census of 1919 reports 826,846 acres of land irrigated by pumping from wells in this state as compared to 276,595 acres in 1909, an increase of 198.9 per cent in ten years. There were 21,561 pumping plants reported in 1919. As such plants now furnish water to about one-fifth of the irrigated area in the state, the importance of the proper selection of the necessary equipment and the cost of its operation is obvious. The proper selection of a pumping plant depends upon many factors which should be carefully considered by prospective pur- chasers. These are: (1) source of water supply; (2) capacity of plant and period of operation; (3) the kind of pump; (4) the class of engine or driving power ; (5) the pumping lift; (6) the initial cost; (7) the power cost ; (8) the cost of fixed charges and attendance. These factors are interdependent and should be considered in connection with one another. Their relative importance will vary with local conditions, and for that reason it is not possible to state definite rules which will apply to all cases. A study of the conditions affecting each factor is therefore necessary in the several cases. * The material in this bulletin was originally prepared in connection with instruction in irrigation in the Short Courses in Agriculture at the University Farm at Davis. It was afterward published in the "Journal of Electricity, Power and Gas." This is the second printing in its present form. The changes from the first reprint consist mainly in the revision of costs, and in additions made to include recent developments in pumping plant practice. t Department of Irrigation, University of California. UNIVERSITY OF CALIFORNIA EXPERIMENT STATION SOUECE OF WATER SUPPLY The source of water supply may be surface water, such as water occurring in rivers, lakes, canals, etc., or it may be ground water. Where surface water is available, the supply should be developed by means of a proper intake, which in the simplest cases will be formed by making the suction pipe of the pump extend into the body of water. Where ground water is available, wells are the most common means of development. No attempt is made in this bulletin to discuss the conditions under which ground water occurs, or the extent and permanence of the supply. It is an important fact that over a long period of years no more water can be pumped from any body of ground water than is replaced from its source of supply. The source in any given case may be seepage from natural stream channels or from canals, percola- tion from irrigated areas, or percolation from direct rainfall. The conditions under which ground water is replenished, however, are frequently complex, and the measurement of the replenishment is difficult. That present rates of pumping are approaching or exceeding the rates of replenishment in some areas of the state is indicated by the lowering of the ground water elevation from year to year. There is as much need for investigation and care in studying the water supply for pumping purposes as there is determining the adequacy of the water supply of a canal system diverting natural stream flow. WELLS Wells may be dug, bored or drilled. The most common type for individual pumping plants in California is a drilled or bored well 10 to 16 inches in diameter, lined with one of the three following types of casing: First: Standard steel screw casing. Second: Single galvanized iron casing No. 12 to 16 gauge, with joints riveted together. Third: Double black steel casing, No. 12 to 16 gauge, known as California stove pipe casing, and used very generally in south- ern California. This casing is made of riveted steel sections two feet long placed with broken joints. The bottom of the casing consists of a starting section 15 to 20 feet long, made of triple thickness, riveted together with a steel shoe at the lower end. Circular 117] SMALL PUMPING PLANTS 3 The well and casing should extend into the water-bearing gravel far enough to give a perforated area equal to at least five times the cross-section area of the well. Slit perforations are made in the casing with an improved cutting tool. These perforations consist of six to eight slits made in each ring or circle, each slit being 12 to 18 inches long and % to % inch wide. A space of 4 inches is skipped after each set of perforations and another ring of slits offset with the adjacent ones is made. Slits should not be over 18 inches long in the case of stove pipe casing. Special forms of perforations and wire windings are sometimes used. General average costs for well boring, exclusive of casing, in the San Joaquin Valley are about as follows: Cost per foot of depth according to depth in feet Diameter of Well in inches to 50 50 to 100 A 100 to 150 150 to 200 7 $ .90 $1.15 $1.50 $2.00 10 1.25 1.50 1.90 2.40 12 1.50 1.75 2.10 2.60 14 1.75 2.00 2.40 2.90 The cost per foot of steel stove pipe casing is about as folio Diameter No . 12 Gauge No. 14 Gauge 7 $1.80 $1.35 10 2.50 1.75 12 2.90 2.05 14 3.30 2.35 16 3.75 2.65 THE CAPACITY OF THE PLANT AND THE PERIOD OF ITS OPERATION The required capacity of the plant will depend on the area to be irrigated, the duty of water or depth of water required on the land, and the period of operation of the pump. For an average loam soil a total depth of 12 inches of water during the irrigation season will be sufficient in the case of young orchards. In the case of a full-bearing deciduous orchard a depth of 18 inches may be required, while for a citrus orchard, 24 inches should be ample. For alfalfa and other forage crops, 24 to 36 inches is representative of good practice. Where the cost of pumping is high, as it is with small plants and high lifts, pump- ing will be profitable only in the case of crops of high return or low water requirements. In order to reduce the cost of pumping the use of excess water should be avoided and all losses should be prevented by careful irrigation and thorough cultivation. If care is taken a young orchard on fairly deep and retentive soil may not require more than 6 to 12 inches of irrigation water, and a full-bearing orchard not 4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION more than 12 to 15 inches during the irrigation season for deciduous trees and 18 inches for citrus trees. To put a depth of 2 feet of water on one acre of land takes a flow of very nearly 1 cubic foot a second for 24 hours. This is equal to a flow of 450 U. S. gallons a minute for 24 hours. By applying this relation to any given case it is possible to determine the size of pump to be employed. For example, to irrigate a 40 acre orchard iy 2 feet deep during an irrigation season of 120 days, requires 60 acre feet of water, or i/ 2 acre foot a day. This result will be obtained by a pump discharging % cubic foot a second, or 110 U. S. gallons a minute, provided the pump is operated con- tinuously 24 hours a day every day during the irrigation season of four months. For a 10 acre orchard the capacity required under the same conditions would be one-quarter of the above amount, that is, 28 gallons a minute, or Via of a cubic foot a second. The two examples above are based on a pump operating continu- ously at given rates. Although continuous operation makes possible a plant of smaller size, it is usually preferable to select a plant of larger capacity and operate it only a part of the time. This is especially desirable for very small orchards, in the case of which continuous operation gives a stream too small for efficient irrigation. The further disadvantages of continuous operation are : First. — Continuous operation requires either continuous irrigation or the use of a reservoir to store the water pumped during the night and at other times when water is not being applied to the crops. Second. — Continuous operation gives a small stream which cannot be applied economically. Third. — Continuous operation means that the water cannot be ap- plied to the different parts of a tract within a short time, so that only a small part of the orchard or farm in question receives water when it is most needed, and the remainder must be irrigated either too early or too late. Fourth. — A small plant is less efficient than a larger plant and requires a proportionately larger power consumption to pump the same quantity of water. In the case of small plants which are operated continuously, reser- voirs are frequently used to store the water pumped during the night and also to give a larger head when the irrigation is going on. A larger head reduces the time required for irrigating and gives greater efficiency in application in that it decreases the percolation loss by flooding the land more rapidly. Circular 117] small pumping plants 5 The reservoirs are usually built by excavating from the area which is to form the interior enough material to make banks with a width of 2 to 3 feet, the side slopes varying from iy 2 to 2 feet in a horizontal direction for each 1 feet in vertical direction. The depth of water stored is usually from 4 to 6 feet. To store a discharge of 450 gallons a minute for 24 hours would require a reservoir about 100 feet square holding water to a depth of 4 feet. Such a reservoir would cost about $140. Larger reservoirs may have an area of as much as one acre. The cost in this case would be about $400, if the land used be taken as worth $100 an acre and the cost of excavation be estimated as 12 cents a cubic yard. Where the soil is pervious there may be considerable seepage from a reservoir. This waste may be reduced by the use of puddled clay, oil, or concrete. Under usual conditions clay puddle or oil linings will cost about one cent a square foot. The cost of such a lining is about equal to the initial cost of constructing the reservoir. Concrete linings usually cost from 3 to 8 cents a square foot, according to the availability of the materials and the thickness of the lining used. A very short period of operation requires a comparatively large pumping plant, thus increasing the first cost of installation, the interest on the capital invested, the depreciation of the plant and the fund necessary to provide for its renewal. A short operation period also requires a larger source of supply, which may not always be available. The flow of water required, for instance, may exceed the capacity of the well, or may so lower the water plane that the cost of pumping will be increased. The rates for electric power, where this is used, are frequently graduated on the basis of the percentage of time that the power is used, the average rate being lower where the use is more nearly continuous. It is frequently desirable to install a pumping plant that will operate from one-half to one-third of the irrigation season only or even for a still shorter period. This method requires a pumping plant some two or three times the size of the plant required for continuous irrigation. The capacity of the pump in each case must be sufficient to give a large enough stream of water to irrigate economically ; even for the smallest orchards a stream measuring at least 5 to 10 miners inches, or about 50 to 100 U. S. gallons per minute is desirable. The table below gives the required pump capacity for various sizes of areas irrigated during different periods of operation. It is based on a depth of irrigation of 6 inches each month. The period of operation is given in number of 24-hour days that the pumping plant is operated each month. These days need not be consecutive; UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Typical installation of Horizontal Centrifugal Pump, direct-connected to motor, placed at bottom of concrete pit. Circular 117] SMALL PUMPING PLANTS 7 for instance, if the operation period is ten days, instead of applying 6 inches of water in one irrigation period lasting ten days where the soil is so porous and gravelly that it will not retain moisture it may be preferable to apply 3 inches at a time in two irrigation periods of five days each during the month. Capacity of Pumps in U. S. Gallons Per Minute Eequired to Give a 6 Inch Depth of Water Each Month, on a Given Area of Land, the Pump Being Operated a Given Number of 24-Hour Days Area Acres 30 days 20 days 15 days 10 days 5 days 2.5 days 1 day 5 19 28 38 56 113 225 563 10 37.5 56.25 75 112.5 225 450 1125 15 57 85 113 170 340 675 1690 20 75 113 150 225 450 900 2250 30 113 169 225 338 675 1350 3375 40 150 225 300 450 900 1800 4500 60 226 338 450 675 1350 2700 6750 80 300 450 600 900 1800 3600 9000 120 450 675 900 1350 2700 5400 13500 The capacity of pump required for smaller or greater depths of water to be applied per month may be easily computed from the values given by proportion. For different areas and different periods of operation the pump capacity may be obtained by interpolation. KINDS OF PUMPS The kinds of pumps generally used in irrigation are (1) ordinary centrifugal pumps, (2) deep well turbine pumps, (3) power plunger pumps, (4) deep well plunger pumps, (5) air lifts. There are in addition, many special types of pumps some of which have already been tried, while others are now being brought forward. The list given above includes the types which have been used for a sufficiently long period and to a sufficient extent to establish their adaptability and dependability. Centrifugal pumps. — This term is used for the ordinary type of centrifugal pump. It does not include deep well turbine pumps, although these operate on the centrifugal principle. Centrifugal pumps are used both horizontally and vertically, the difference being that in horizontal centrifugal pumps the shaft of the pump is horizontal, while in vertical pumps it is vertical. A centrifugal pump consists of a circular casing with its inlet or suction end connected to the center, and its outlet or discharge end forming a tangent to the outer circumference. Inside the casing is 8 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION the runner or impeller which is keyed on the shaft and revolves with it. It is formed of curved vanes closely fitting the casing. When it is in operation the impeller, by its revolutions, imparts to the water between the vanes a velocity which forces it away from the center of the casing toward the perimeter or rim of the casing and from there through the outlet and up the discharge pipe. This process produces a partial vacuum at the center of the impeller and thus induces a flow through the suction pipe into the casing. The number of revolutions of the runner or speed of the pump, has a definite relation to the head or lift against which the pump is working, and for every head there is a speed at which the pump works most efficiently. The rate of this speed can be obtained from the pump manufacturers. It is important that the pump be connected to an engine or motor which will give it the proper speed. Overspeeding is preferable to underspeeding, but either alternative reduces the efficiency of the pump. Simple centrifugal pumps which are specially designed and driven at a sufficiently high rate of speed may be used for lifts of a height considerably over 100 feet, but usually the stock pump obtainable from the manufacturers is not suitable for lifts of over 75 feet. For the smaller sizes the total lift should not exceed 50 feet. For higher lifts compound or multi-stage centrifugal pumps are used. These consist of two or more pumps connected in a series in which the dis- charge of the first pump or stage is delivered into the suction of the next pump and so on, according to the number of stages. Usually 75 feet to 125 feet is allowed for each stage. Centrifugal pumps are usually denoted by a number which repre- sents the diameter of the discharge outlet measured in inches. The capacity at which each size of pump is most efficient will vary to some extent with the speed of the pump, which in turn will depend on the total lift pumped against. Such pumps, therefore, can not be rated accurately. The capacities given in the accompanying table are repre- sentative of the discharge to be expected of the usual types of pump under average conditions. The actual discharges of different makes of pumps operating under different conditions as regards lift may vary considerably above or below the figures given. To start a centrifugal pump the suction pipe and the pump itself must be filled with water, or primed. This may be done by closing the discharge pipe with a check valve and connecting the suction end of a hand pump to the top of the casing. For small pumps and low lifts a foot valve attached to the end of the suction pipe may be used, and the pump primed by pouring water into the casing or suction pipe. The disadvantage of a foot valve is that, if the water is not Circular 117] SMALL PUMPING PLANTS Vo vcNuqt /e/ease. coil Platform or jrof.-ia o// ptrforoJco' on to-vcr es*d <5-frOirtcr ortd foot ro/,c Details of Vertical Pump Installation 10 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION clear, a small stone or twig may lodge itself in the valve and prevent priming. Such an accident may make it necessary to uncouple the suction pipe in order to remove the obstruction. u o Si* pa ® 5 c ^ o S § ft = 3 .as .a« Number of Acres Irrigated 6 Inches Deep Each Month for a ^ a3'™ **"* Given Operation Period •is 8 a a s s 2 2 55 '-do G3 O OC5 °3 ^ ft c3 O o A 30 days 20 days 15 days 10 days 5 days 2)4 days 1 day 2 100 .22 27 18 13 9 4y 2 2% 9 /l0 2% 150 .33 40 27 20 13 6V2 3V4 l%o 3 225 .50 60 40 30 20 10 5 2 3% 300 .66 80 53 40 27 13 6V2 2% 4 400 .90 110 71 55 35 18 9 3% 5 700 1.60 190 127 95 63 32 16 ey 3 6 900 2.00 240 i60 120 80 40 20 8 7 1200 2.70 320 213 160 107 54 27 IO2/3 8 1600 3.50 430 287 215 143 72 37 14% The pump must be placed as near as possible to the water level in order to keep the suction lift down. While theoretically the suction lift may be as great as 33 feet at sea level, and about 30 feet at an elevation of 3000 feet, it is desirable not to exceed 20 feet, while a still lower lift is preferable. The horizontal centrifugal pump is preferable where the depth from the surface of the ground to the water plane is not great. Where the depth is great, however, a verti- cal pump in a deep pit may be used. A centrifugal pump with a horizontal shaft is usually more efficient than a vertical centrifugal pump, as it eliminates the difficulty of properly balancing the end thrust obtained with the vertical shaft. The efficiency of a plant may be increased by reducing the friction in the suction and discharge. There should be as few bends as possible in the pipes. Losses may be reduced by using elbows with long turns. The suction and discharge pipes should be larger than the intake and outlet opening of the pump and joined to it with a reducer. The diameter of the suction pipe, and what is more important that of the discharge pipe, should be one and a half times as great as the diameter of the intake of the pump, and if the discharge pipe is long it may be economical to make the diameter even larger. Where the source of the water supply is a surface body of water, enlarging the lower end of the suction pipe will further decrease the friction. This may be done by attaching a funnel-shaped section about three times Circular 117] SMALL PUMPING PLANTS 11 Deep Well Turbine Centrifugal Pump the diameter of the suction pipe in length and about one and a half times as wide as the diame- ter of the pipe at its large end. The larger opening at the en- trance to the suction pipe will decrease the tendency to draw sand or trash into the pump. When the water carries weeds, gravel, or other extraneous ma- terial, a strainer should also be used. The total area of the strainer should be at least twice that of the suction pipe. The discharge pipe should not carry the water any higher than is necessary. Deep well turbine pumps. — This term is used to designate a type of centrifugal pump adapted for operation within the limited space conditions of the well casing. This makes it nec- essary to give to the impellers, or bowls as they are more gener- ally called, a smaller diameter, thus causing a reduction in the amount of lift obtainable from each set of runners. For this reason an additional stage or bowl is generally used for every 15 to 30 feet of lift so that deep well turbine pumps are practi- cally all multi-stage. The driv- ing shaft is carried to a pump head at the surface of the ground, the weight and friction of the revolving parts being car- ried by the pump head. For deep well turbine plants the wells are generally of somewhat larger diameter than for other 12 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION types. They may be as large as 20 to 24 inches in diameter. The pump is usually submerged so that priming is unnecessary. Be- low the level of the pump the diameter of the well is determined by the materials used and yield desired, and is frequently made smaller than the diameter above. The discharge pipe surrounds the driving shaft. The shaft may be separated from the discharge by an enclosing pipe. Discharge Suction Plunger Pump, Double Acting Cylinder Power plunger pumps. — This term is used for piston or plunger pumps of the ordinary types used for pumping from sources near the surface where the total operating lift is large. Pumps of this type, used for irrigation, do not differ in principle from those used under similar conditions for other purposes, as for example for a municipal water supply. The pump consists of one or more cylinders, in each one of which a piston or plunger moving backward and forward draws the water into the cylinder and forces it up the discharge pipe. When the cylinder has only one suction valve and one discharge valve, the piston as it moves in one direction causes suction, and the conse- quent displacement in the opposite direction forces the water through the discharge pipe. When the pump has two sets of valves so arranged that there is a discharge for each displacement of the piston, it is known as a double acting pump. When it has two cylinders, it is known as a duplex pump; when three cylinders, as a triplex pump. In either case it may be either double acting or single acting. The cylinders Circular 117] small pumping plants 13 with the driving gears or pulleys are assembled and built at a height above the water plane not exceeding the suction lift. The capacity of the pump will depend on the diameter of the cylinder, the length of the stroke of the piston, and the number of strokes or revolutions per minute. The capacities of a few sizes of plunger pumps are indicated as follows : Capacity of Double Acting, Single Piston Pump Diameter of vater cylinder Length of stroke Revolutions or strokes per minute Discharge in U. S. gallons per minute 3 in. 5 in. 40 12.4 4 in. 5 in. 40 21.6 5 in. 5 in. 40 34 6 in. 6 in. 40 58 7 in. 6 in. 40 80 8 in. 6 in. 40 104 Capacity of Single Acting, Triplex Piston Pump Diameter of water cylinder Length of stroke Revolutions or strokes per minute Discharge in U. S. gallons per minute 3 in. 4 in. 50 18 4 in. 4 in. 50 32 4 in. 6 in. 50 50 5 in. 6 in. 50 76 5 in. 8 in. 45 91 6 in. 8 in. 45 131 7 in. 8 in. 45 180 7 in. 10 in. 42 210 8 in. 10 in. 40 270 8 in. 12 in. 40 310 9 in. 10 in 40 340 Capacity of Double Acting, Duplex Pump Diameter of water cylinder Length of stroke Revolutions or Discharge in U. S. strokes per minute gallons per minute 2% in. 4 in. 75 20 3 in. 4 in. 75 36 3y 2 in. 6 in. 60 58 4 in. 6 in. 60 78 5 in. 6 in. 60 120 6 in. 6 in. 60 174 5 in. 10 in. 50 170 6 in. 10 in. 50 245 7 in. 10 in. 50 334 8 in. 12 in. 50 522 9 in. 12 in. 50 660 14 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION ■^s^'S&v The sizes of pumps and their capacities vary with the different manufacturers. The values stated above show the approximate range of the different sizes. For small capacities the double acting single piston pump may be used. Deep well plunger pumps. — The action of these pumps is similar to that of the power plunger pumps, but like the deep well turbines, the deep well plunger pumps are adapted to the operating and space conditions of the well casings. They consist of a cylinder in which two plungers operate with valves. The lower plunger is connected to a solid rod which fits into a hollow rod to which in turn the upper piston is con- nected. The plungers are so operated by the driving power that the pump is double acting, one plunger moving up while the other moves down, so that there is a continuous discharge of water. Above the cylinder and connected to it, is the vertical discharge or column pipe into which the water passing through the valves in the plunger discharges. The cylinder is about two inches smaller in diameter than the well casing and about one inch smaller than the delivery pipe ; the cylinder and delivery pipe are both lowered into the well until the plungers are under water. At the surface the driving power and circular motion of the belt is transmitted to the driving rods by means of gears and levers which are combined into a power head designed to produce overlapping strokes, so as to eliminate to some extent the pulsations of the discharge. These may be further decreased by an air chamber. The size of these pumps range from those with 6 inch cylinders and 28 inch stroke to those with 16 inch cylinders and 36 inch stroke. The number of strokes range from sixteen to twenty-four a minute, depending on the lift and the size of the pump. The maximum lift is about 350 feet. The capacity is usually less than 300 gallons a minute but it Sim mm Circular 117] SMALL PUMPING PLANTS 15 may be as much as about 1000 gallons, the capacity of the largest pump which has an extra long cylinder. Air lift pumps. — Air lift or compressed air pumping plants consist of one or more air lift pumps, the air compressor with its receiver and the motive power used for compression, and the piping necessary to deliver the compressed air from the receiver to the pumps. Each pump consists of: (1) the discharge pipe, which is smaller than the well casing and is placed inside of it, and for most efficient operation should extend below the water surface to a depth about equal to the pumping lift as measured from the water surface; (2) the air pipe, which is usually inside the discharge pipe, but may, if the well is enough larger than the discharge pipe to permit it, be placed outside the pipe and connected at its lower end by means of standard fittings or special castings; (3) the foot piece, which is a special casting con- nected to the lower end of the air pipe and so designed as to admit the air evenly in small bubbles (there are various designs of patented foot pieces, but there is little difference in their efficiency) ; (4) the tail piece which is a slightly enlarged extension of the lower end of the discharge pipe below the foot piece. The air is delivered through the foot piece at pressures varying according to the pumping lift and the ratio of diameters obtaining between the air pipe and the water pipe. Its expansion and displacement produces the lifting power. The relation between the volume of air supplied and the volume of water pumped for different lifts has been found by experi- ment to be as follows: Lift in feet 20 30 50 100 200 Cubic ft. of air Eatio Cubic ft. of water 3.2 3.5 4.1 5.4 7.7 In this table the lift is the distance from the surface of the water in the well to the end of the discharge pipe, and the volume of air is given in cubic feet of free air, under ordinary atmospheric pressure. The velocity of the water in the discharge pipe, as based on the volume of water pumped should not exceed 5 feet a second, if friction losses are to be kept down. The compressor may be connected to a steam engine, a gasoline engine, or an electric motor. The compressed air passes from the air cylinder to the receiver, which is used to store the air and equalize the pressure. From the receiver the air is conducted through pipes to the wells. 16 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The efficiency of a properly installed compressed air plant as calculated from the ratio of actual water horsepower developed to the indicated horsepower in the cylinder of the engine, is generally between 20 and 30 per cent. Air lift pumps are used for pumping from several wells into a common place of supply as the installation of such a pump at each well is relatively simple, which is an advantage where the yield at each well is so small that it is necessary to operate a series of wells to obtain the desired supply. This method may also be used in a well with crooked casings in which deep well types of pumps can not be operated. ADAPTABILITY OF THE SEVERAL TYPES OF PUMPS FOR SMALL PUMPING PLANTS Where the source of water supply is a stream or surface body of water, the choice usually lies between a power plunger pump and a centrifugal pump, and will depend largely on the lift and capacity required. Power pumps are best adapted to high heads, those of above 75 feet and to small or moderate volumes of water, usually under 200 gallons a minute. Under these conditions the efficiency of a power pump is usually greater than that of a centrifugal pump. For greater volumes the plunger pumps are relatively expensive, so that centrifugal pumps are usually preferable, unless the lift is excessive. The centrifugal pump has the advantages of being simple in construc- tion, with no parts to get out of order, and of being cheaper than a power pump. When the source of water supply is ground water with the water table in the well at a depth below the surface of less than about 40 feet, making a deep pit unnecessary, the choice lies between a centrifugal pump, a power plunger pump, and an air lift pump. The selection between a centrifugal and a power plunger pump will depend on a consideration of the lift and capacity demanded as explained above. Air lift plants have a low efficiency, and require a depth of well below the water table about equal to the lift as measured from the water-table so that they are hardly to be considered in connection with small separate pumping plants. They are best adapted to a large number of wells (six at least, or preferably more) placed close together. An air lift pump may be used to advantage for a well which is too crooked for the other types of pumps. Where the source of the water is ground water developed by deep wells with the water table at a depth below the surface of 50 to 200 feet or more, the choice is usually between a vertical centrifugal Circular 117] SMALL PUMPING PLANTS 17 pump in a pit, a deep well turbine, and a deep well plunger pump. Deep well plunger pumps are best adapted to lifts of over 100 or 150 feet, and for discharges of not over about 300 gallons a minute. Their efficiency is greater than that of centrifugal pumps, but the cost of repairs and depreciation is also greater. Deep well turbines have a higher first cost than ordinary centrifugal pumps, but do not require a pit. Deep well turbines may be used for larger capacities than deep well plunger pumps. They are now used to a greater extent and on lower lifts than formerly. Where the ground water fluctuates, both of the deep well types of pump have the advantage of being submerg- ible, so that lowering of the pump may not be required in years of low water elevations. The selection of a pump should be made only after careful con- sideration of the first cost and the annual cost of fuel, operation, and maintenance. Where the lift is high, the power cost will be consider- able, and it is good economy not to select the cheapest pump obtain- able, but rather one that is guaranteed for its efficiency. On the other hand, if the pump is to be operated during only a very small portion of the season, it would be poor economy to invest a large capital in a high grade pumping plant to save in power cost. » METHODS OF DEIVING THE PUMPS The driving power for these pumps is generally either a gasoline engine or an electric motor. Centrifugal pumps are usually either directly connected with the source of power or else connected by means of belts, gears, or chains. Plunger pumps are connected by belts or gears. Direct connection is preferable when possible; it is more efficient and eliminates the adjustment of the belt necessary with the belt driven pumps. The connection of the pumps with the driving power must be such that they will be given the speed or number of revolutions a minute for which they are designed and at which the highest degree of efficiency is obtained. For this reason direct con- nection can only be used where the driving power and the pump have the same speed. The speed of centrifugal pumps is usually high; so is that of electric motors; and for this reason these two may, if they are properly designed, be directly connected. The connection is usually made by means of a flexible coupling. Gasoline engines are generally operated at a much lower speed than centrifugal pumps, and are therefore not connected directly unless the engine and pump are specially designed. When the heads are low and subject to wide variation, to obtain maximum efficiency with direct connection, it is 18 UNIVERSITY OF CALIFORNIA— EXPERIMENT STATION Belt Driven Submerged Pumps Circular 117] small pumping plants 19 necessary to change the runners of the pump to correspond to the different heads. Some pumps are so manufactured that this change may be made, but under such conditions it is easier to use belt con- nection and vary the size of the pulleys. Because power plunger pumps are operated at a low speed, they are not connected directly to the driving power. When the connection is made by gears, belts, or chains, the driving gear and driven gear, or the driving pulley and the driven pulley must be so proportioned to one another that the pump will be given the correct speed. When a plunger pump is built with a steam engine as a single machine, with the piston or plunger of the water cylinder on the same driving rod as the piston of the steam cylinder, it is called a direct acting steam pump. The fuel consumption of such a steam pump is greater than that of a steam driven plunger pump. Deep well plunger pumps are usually equipped with gears and levers combined and connected with the driving rods of the pump, forming what is called the pump head, the object of which is to con- vert the circular motion of the driving power and transmit it to the driving rods of the pump. The engine or motor is usually connected to the pump head by belts, but it may be connected by means of gears. The power required to lift water is indicated in horsepower. One horsepower represents the energy required to lift 33,000 pounds to a height of one foot in one minute ; this is equivalent to raising 3960 gallons of water to a height of one foot every minute. By using this relation one is enabled to calculate the net horsepower required in any given case by multiplying the discharge of the pump in gal- lons a minute by the total lift in feet and dividing the product by 3960. The result obtained represents the useful water horsepower required to lift the water. The horsepower delivered by the engine or motor to the belt or gears, when the pump is belted or geared to the engine, or to the pump itself, when it is directly connected, is the brake horsepower, and must be greater than the useful water horsepower in order to allow for the loss of energy in the pump and transmission. Gasoline engines and motors are rated on brake horse- power. Gasoline engines are frequently over-rated. The combined efficiency of a pumping plant represents the ratio of the useful water horsepower to the rated horsepower of the engine or motor, and will vary considerably with the type of pump and method of connection employed, and the care taken in operating both pump and driving power at the proper speed. In ordinary field practice a good pumping plant properly installed, should obtain the 20 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION overall efficiency indicated in the following table. The average effi- ciencies of ordinary centrifugal pumps and deep well turbines for the same capacities and lifts are at)out equal. The total power requirements of a pumping plant should be figured on the basis of the total lift measured from the drawn down water level when the pump is in operation. When the pump discharges freely at its outlet, without a discharge pipe extension, the total lift is the difference in elevation between the water level in the well when the pump is in operation and the outlet end of the discharge pipe. It includes the draw down or the distance which the ground water lowers at the well when the plant is operating in order to supply the head necessary for the movement of the ground water to the well and through the perforations of the well casing. The amount of draw down varies with the quantity of water pumped and the texture of the water bearing material. It is frequently in excess of 10 feet and may exceed 30 feet in the case of fine materials heavily pumped. When the pump outlet is connected to a discharge pipe of any considerable length the total lift must include the head or additional lift corresponding to the frictional resistance offered by the pipe. Efficiency of Centrifugal Pumping Plants and Brake Horsepower Eequired Per Foot of Lift No. of centrifugal pump Discharge in U. S. gals. per minute Water horsepower per foot of lift Efficiency percentage Brake horsepower per foot of lift 2 100 .025 30 .081 2V 2 150 .038 35 .11 3 225 .057 40 .14 3% 300 .08 45 .18 4 400 .10 45 .22 5 700 .17 50 .34 6 900 .23 50 .46 7 1200 .31 50 .62 8 1600 .41 55 .75 The efficiency of power plunger pumps varies with the size of the pump and with the lift. A greater efficiency is obtained with the higher lifts and the larger sizes. The efficiency of properly installed plunger pumps and the horsepower required for operation in the case of various lifts are given in the following table: Circular 117] SMALL PUMPING PLANTS 2 Diameter Length of of I Capacity in U. S. gals. r- per minute Efficiency and Brake Horsepower of A for lifts cylinder stroke 50 ft. 100 ft. 150 ft. 200 ft. 250 ft. 3 in. 4 in 18 Efficiency .30 .40 .42 .45 .45 Horsepower .75 1.1 1.6 2.0 2.5 4 in. 4 in. 32 Efficiency- .35 .50 .60 .65 .65 Horsepower 1.2 1.5 2.0 2.5 3.1 4 in. 6 in. 50 Efficiency- .35 .50 .60 .65 .65 Horsepower 1.9 2.5 3.1 4.0 4.8 5 in. 6 in. 76 Efficiency .40 .55 .65 .70 .70 Horsepower 2.4 3.5 4.4 5.5 6.7 5 in. 8 in. 90 Efficiency .40 .55 .65 .70 .72 Horsepower 2.8 4.1 5.2 6.5 7.8 6 in. 8 in. 131 Efficiency .45 .60 .65 .70 .72 Horsepower 3.6 5.5 7.5 9.3 11.4 7 in. 8 in. 180 Efficiency .45 .60 . .65 .70 .72 Horsepower 5.0 7.5 10.5 13.0 15.5 7 in. 10 in. 210 Efficiency .50 .65 .70 .75 .78 Horsepower 5.25 8.0 11.0 14.0 17.0 8 in. 10 in. 270 Efficiency .50 .65 .70 .75 .78 Horsepower 6.75 10.25 14.50 18.25 22.1 9 in. 10 in. 340 Efficiency .50 .65 .70 .75 .78 Horsepower 8.5 13.0 18.0 23.0 28.0 The plant efficiency for deep well plunger pump plants as ordinar- ily installed and operated was found from measurements made on a number of pumping plants in southern California to be from 35 to 60 per cent. With proper installation and operation the plant efficiency or ratio between useful water horsepower and brake horse- power should be from 50 to 65 per cent. The plant efficiency of air lift pumps, expressed as the ratio be- tween the useful water horsepower and the indicated horsepower in the engine cylinder, was found from tests on a number of plants in southern California to average a little less than 20 per cent ; but with a good installation an efficiency of 30 per cent may be obtained. The tables just given will indicate the size of the driving power required. It may be either a gasoline engine or an electric motor. A gasoline engine generally uses comparatively high grade distillate, such as is commonly called engine gasoline. During the past few years engines which have been developed to use cheaper low grade distillates or crude oils have been put on the market. The main difficulty with these types is in the asphalt residuum which may occur upon the vaporization of the oil. Satisfactory results, however, have been obtained with a number of engines installed in California. The purchaser of an engine of this type should visit one or more 22 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION engines of the same make which have been in actual operation for at least one season and find out from their owners what difficulties and troubles, if any, have developed in operating them. The main ad- vantage of this type of engine is that it may be run with fuel of very low price. The methods of connecting the engine with the pump have been already considered. Other factors being equal, direct connection is preferable when it is possible. A few general considerations as to the types of driving power are given in the following paragraphs. For small plants irrigating a few acres, the steam engine, although very reliable, is seldom used in California, and need not be considered except where coal or wood is very cheap as compared to gasoline. It has proved economical under such conditions for some small plants in Oregon, Washington, and New Mexico. For larger areas, moreover, and where coal or oil is cheap, it may be more economical than either a gasoline engine or an electric motor. A gasoline engine is fairly reliable if it is strongly built and op- erated with care. Cleanliness and proper attention are necessary. All its parts and bearings should be kept well adjusted and properly oiled, to which end it should be examined at least every two or three hours. The engine should be regulated by means of a governor so as to give proper speed to the pump. To keep down the fuel consump- tion the gasoline feed should be so adjusted that there will be a miss in every ten or twelve explosions, and the engine should be worked up to its full rated capacity. Over 75 per cent of the troubles occur- ing in connection with gasoline engines are due to the sparking device. The difficulty here can usually be remedied by cleaning all connections free from oil, scraping the ends of wires, tightening screws, replacing the batteries, and removing carbon from contact points. Electric motors are reliable and easy to operate since they require very little attention. FIKST COST OF THE PLANT The first cost of a pumping plant depends on the grade of machin- ery to be installed, the cost of transportation, and the expense of installation. Because of these factors accurate estimates of costs cannot be given. The approximate cost values given below will be of help, however, to the landowner who is considering the feasibility of a pumping plant. They represent the prices at the factory and do not include transportation and installation. Circular 117] SMALL PUMPING PLANTS 23 Approximate Cost of Single Stage Centrifugal Pumps No. of pump Capacity in gals, per minute Cost for belt connection Cost for direct connection 2 2% 100 150 $ 65 80 $130 170 3 225 95 200 3% 300 110 215 4 400 120 230 5 700 145 325 6 900 180 360 7 1200 240 430 8 1600 275 500 The cost of two-step centrifugal pumps of the same size would be about four times the values indicated. The cost of deep well turbine pumps is greater than of the ordinary centrifugal pumps and varies more widely with the size of the well used and the lift. A deep well turbine installed in a 12 inch well with a lift of 60 feet discharging 450 gallons a minute and operated by a 15 horsepower motor would cost for installation about $1500 exclusive of the cost of the well. Approximate Cost of Triplex Single Acting Power Pump Diameter of water cylinder in inches Length of stroke in inches Capacity in gals, per minute Height of lift in feet Cost 4 8 65 75 to 100 $170 5 10 130 100 250 6 12 220 100 340 4 6 48 175 225 5 8 91 175 325 7 8 180 175 450 8 10 270 175 700 8 12 310 175 750 Horsepower Cost of electric motors 1200 revolutions per minute Cost of gasoline engines Cost of oil engines 2 $ 70 $100 3 85 120 5 110 180 10 240 400 $750 15 280 500 950 20 310 800 1000 25 360 1500 30 415 2000 40 480 2900 50 550 3400 24 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The costs indicated above are for pumps and engines, and do not include the accessories of the plant, the foundation, the labor of in- stallation, or the housing. For an electric plant the cost of trans- formers should be added unless these are supplied by the electric company. The accessories will include the suction and discharge pipes the valves and fittings, the priming pump, and the connection between pump and engine. The suction pipe is usually made of steel; the dsecharge pipe may be steel or wood banded pipe, and should cost, delivery included, as follows: Approximate Cost of Pipes Safe for 150 ft. Head Diameter of pipe Wood banded pipe Steel pipe in inches cost per foot cost per foot 4 $ .35 $ .40 6 .50 .55 8 .65 .65 10 .80 .80 12 1.00 .95 14 1.20 1.05 16 1.40 1.20 18 1.60 1.60 20 2.00 1.80 As a rough estimate of the total cost of valves, priming pump, all fittings and suction pipe, not including discharge pipe, about 10 per cent of the cost of pump and engine may be taken for a gasoline plant and 20 per cent for an electric plant. The cost of installation should not exceed 5 per cent. The cost of a building to house the plant will range from about $25 for a small plant to $100 or more for a larger plant. The cost of transportation and hauling will depend upon the freight charge and the distance from the station to the point of in- stallation. FUEL CONSUMPTION AND FUEL COST The selection between a gasoline engine and an electric motor in a given case will depend largely on the comparative cost of gasoline and electrical energy and the conditions of operation. A gasoline engine is usually guaranteed for a fuel consumption of one-eighth of a gallon per rated or brake horsepower an hour. A new engine well adjusted will come up to this standard of efficiency, but an engine that has been operated for some time will consume about Y 6 of a gallon of engine gasoline or distillate per brake horsepower an hour. Circular 117] small pumping plants 25 Electrical energy is measured in kilowatts. A kilowatt is equal to l x /3 horsepower. As the energy consumed by a motor is measured on the inlet side of the motor, one kilowatt of electrical energy de- livered to the motor will usually deliver about 1.1 brake horsepower. Based on this ratio, %o of a kilowatt hour will be required to produce 1 brake horsepower hour. The values indicated above show that to produce 1 brake horse- power hour either Vq of a gallon of distillate or %o of a kilowatt hour of electrical energy is required. The table below which is based on these figures show the cost of fuel per brake horsepower hour for several equivalent cost values of power. In the same table is also given the power cost of pumping one acre foot of water through one foot lift, assuming a plant efficiency of 50 per cent and 75 per cent. Power companies engaged in supplying electrical energy for use in irrigation pumping must have always available a sufficient amount of power to meet the maximum demand that may be made on the system at any one time. It may require nearly as much in- stalled capacity to meet a load which operates only one-half of a given time as it would if the same load operated full time, if the conditions of use in question are such that the period of use of all the part time load comes at the same time. For this reason most schedules of rates for electricity for pumping contain either a mini- mum charge, which must be paid if any power is used, or are arranged on a sliding scale by which the cost for a unit of power consumed decreases with an increase in the extent of use of the plant. Some power companies formerly used rates according to which the pay- ment was based on the extent of the maximum demand or connected load, requiring the payment of a certain price a horsepower for the season, the cost being the same regardless of the proportion of the time the plant might actually be used. Such rates naturally resulted in the installation of smaller plants to be operated more nearly continuously, the plant being reduced in order to keep down the size of the motor required. Some form of rate with a minimum price per horsepower per month plus a rate per kilowatt hour consumed, or a rate in which the price per kilowatt hour is decreased as the time of operation a month increases is now more usual. The actual rates also vary with the size of the plant and with the costs of service of the different power companies. Under usual conditions for the small irrigation pumping plants a typical average cost of power would be about 2 cents a kilowatt hour. The rate may be considerably less for small plants if they are operated more nearly continuously. It is also less for large plants. 26 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION Cost of Fuel Per Brake Horsepower Per Hour Equivalent unit cost power of fuel or Fuel costs (in cen ts) Per brake , horsepower per hour in cents Per acre-foot of h water igh lifted 1 foot r Cost of electric in power per k.w.h. al. in cents Cost of oil cents per g with 50% efficiency with 75% efficiency 6 1.11 1.00 2.75 1.83 8 1.50 1.33 3.70 2.45 10 1.85 1.66 4.60 3.05 12 2.22 2.00 5.50 3.65 14 2.60 2.33 6.40 4.25 16 3.00 2.66 7.30 4.90 18 3.33 3.00 8.25 5.50 20 3.70 3.33 9.15 6.10 22 4.10 3.66 10.10 6.70 24 4.35 4.00 11.00 7.35 26 4.80 4.33 11.80 7.95 FIXED CHARGES AND ATTENDANCE A. Fixed charges. — The cost of the installation of a pumping plant represents a capital which, if invested, would bring in an income equivalent to the interest on the original cost. It is therefore neces- sary to consider this interest as part of the cost of operation. To this amount should be added the annual cost of repairs, maintenance, and renewal. These items of cost represent the fixed charges for the plant. After six or eight years a gasoline engine may need to have its cylinders rebored and to have a new piston provided. The cost of these repairs is about one-tenth of the cost of a new engine. With ordinary care the life of a gasoline engine may be estimated as 10 years, and the life of an electric motor about 15 to 20 years. The fixed charges on the entire plant may be estimated as follows: Fixed Charges Gasoline Engine Electric Plant Plant Depreciation and renewal 8% 5% Repairs and maintenance 3% 1% Interest 6% 6% 17% 12# B. Attendance. — An electric motor requires a minimum of attend- ance, while small gasoline plants require frequent inspection. The cost of attendance for an electric motor pumping plant should not exceed 5 cents an hour, and that for a gasoline engine plant 10 cents an hour. While electric motors and gasoline engines are usually operated by the irrigator himself, the time used in attendance is valuable and a charge should accordingly be made for it. Circular 117] small pumping plants 27 THE FINAL SELECTION OF THE TYPE OF PLANT The final selection of a pumping plant should be made on the basis of a careful consideration of the factors which have been stated. The best size of plant, the period of operation, the kind of driving power, can be correctly determined only by a final consideration of the cost of installation and cost of operation. When electric power is avail- able, the choice lies between a gasoline engine and an electric motor. The electric motor requires a minimum of attendance. It is, further- more, reliable, and its first cost is much less than that of a gasoline en- gine. For these reasons, if electric power is available, an electric motor is usually preferable, and may prove to be more economical, even should the cost of electrical energy be higher than the fuel cost for a gasoline engine. The application of the information and cost data previously given to particular cases is illustrated by the following examples : A 20-acre orchard is to be irrigated by pumping from a surface body of water where no wells are required. The quantity of water to be applied is 6 inches a month, and the total depth in one season, 18 inches. The lift in this case is 50 feet, and the discharge pipe employed is 200 feet long. Engine gasoline or distillate costs 12 cents a gallon. Assuming that the pump is operated one-third of the total time, or ten twenty-four hour days each month, a pump capacity of 225 gallons a minute will be required. This discharge is obtained with a No. 3 centrifugal pump and 7 horse-power engine, as has been shown in previous tables. The discharge pipe of the pump will be 4 inches in diameter. The first cost of the plant and the annual cost of its operation will be about as follows: First Cost of Plant No. 3 centrifugal pump $ 95.00 7 horsepower gasoline engine 250.00 Priming pump, suction pipe, fittings, etc 35.00 Freight charges and hauling 30.00 Wood-banded discharge pipe, 200 feet of 4 in. diameter 70.00 Installation, 5 per cent of cost 25.00 Building to house plant 60.00 Total cost $565.00 Total Annual Cost of Operation Fuel cost of 7 brake horsepower engine for 3 periods of 10 days each, of 720 hours = 720 x 7x2.00= $100.80 Fixed charges at 17 per cent of first cost 95.20 Attendance, 720 hours at 10 cents 72.00 Total cost for 20 acres - $268.00 Cost per acre, $13.40. 28 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION In the following examples, costs are given for pumping plants using centrifugal pumps with lifts of 50 feet, delivering 3 irrigations of 6 inches each in depth a season to areas of 20, 40 and 80 acres. Tables for plants of different sizes operating different proportions of the season are worked out. It is assumed that the discharge pipe used is 200 feet long. No costs for wells or pits have been included. In the case of pumping from wells the total cost of the plant should be increased by the cost of drilling and casing the well, and the cost of operation by the interest and depreciation on the well. Estimated Cost of Pumping with Gasoline Engines and Centrifugal Pumps Under Selected Conditions £°g a -5 h a «*h c^.2 a .s » © teS« *u - *S «2 S £~ ^ «« £ ft ° g o .m^ ° ft ^ u ° d Annual operating cost per acre with 18 a o w— o> «j ^ S ,3 § inches total depth of water per acre applied, 3=3 lift 50 ft., cost of fuel 12c per gal. ft £ Fixed Attend-