i Publication of The College of UNIVERSITY OF CALIFORNIA W- CALIFORNIA AGRICULTURAL Experiment Station Extension J. CIRCULAR 418 .For a majority of farms, concrete pipe irrigation systems offer the best known method of distribution when they are properly designed and installed. This circular is planned to help the California farmer decide whether he should install such a system, and if so, to help him choose the best pos- sible one for his needs. It describes the various structures, and gives design and installation details. A sample contract, and specifications are also in- cluded. Much of the information is technical, and will be useful primarily to the engineer and to the person installing the system after it has been designed. The circular is so organized, however, that the farmer need not concern himself with the technical material unless he wishes to do so, but he should find the general information of value if he is considering installation of a concrete pipe system. THE AUTHOR: Arthur F. Pillsbury is Professor of Irrigation and Irrigation Engineer, Experiment Station, Los Angeles. L (length . of line in feet) e^IOOO 100 600 400 200 100 80 60 40 20 H Total loss in line with uniform discharge along entire length (ft. of water ) For 10" pipe For 6" pipe 20 10- 5 2 -: 20 ^—10 5 For 8" pipe 10 : - 5 2 I For 4" pipe Fig. 18. Nomongraph for design of gated surface pipe lines. Find unknown quantity by placing straightedge across sheet intersecting known values. (SOURCE: Unpublished friction loss data of Professor CN. Johnston, University of California, Davis; and assumption that friction loss with uniform discharge along entire length of line is one third of friction loss with full flow to end of line.) (discharge in c.f. s. per foot of pipe) e-1.0 ^-0.6 10 -0.4 0.2 0.1 0.06 0.04 0.02 — 0.01 0.006 H0.004 ^-0.002 0.001 Digitized by the Internet Archive in 2012 with funding from University of California, Davis Libraries http://archive.org/details/concretepipefori418pill ,' WOULD A CONCRETE PIPE SYSTEM HELP YOU? w, ith more and more demands on our limited water supply, there is increasing need for more efficient use of irrigation water. One important method of meeting this problem is the use of concrete pipe distribution systems. Generally speaking, plain (nonreinforced) concrete pipe irrigation systems are used to distribute the water from, at, or near the high point of the farm. If lifts in excess of about 20 feet, vertical, are required, special heavy wall or reinforced con- crete pipe is used. Because such cases require special design for each individual installation, they are not discussed in this circular. On a majority of California farms, concrete pipe distribution systems will save money, despite their initial cost, because of savings in water, in land, in maintenance, and in irrigation labor, and because drainage problems and weed problems will be less severe. ADVANTAGES Little loss of land. Practically all of the system is buried, consequently no significant amount of land is re- moved from crop production. Labor saving. Control of the water is simple, and usually requires much less irrigation labor than do other sys- tems. The labor is often only 25 to 50 per cent of that required with earth ditches. Permanence. Well-made pipe, properly installed, has long life and high carrying capacity. Maintenance costs are usually small. No seepage. The systems are es- sentially watertight conduits. Water is saved, and drainage problems are lessened. Ease of distribution. This is es- pecially important where land is rough and uneven. Water can be run across swales or boosted uphill — a procedure not possible with canals or ditches un- less they have elaborate structures. Where adaptation to the lay of the land requires water to be under high pres- sure, proper reinforced or heavy wall concrete irrigation pipe is substituted for plain pipe. No ditchbank weed problems. There are no ditches to become choked with weeds that hinder flow of water. Weeds in such ditches may harbor harmful insects. In addition, weed seeds may be carried, by the water, to the fields. These problems do not exist with pipe lines. Better control. Better and easier control of the flow of water means that more efficient and better irrigation is possible. LIMITATIONS Less advantage with larger flows. Efficiency and economy of irri- gation of flooded field crops can be im- proved by using large flows of water. The cost of concrete pipe lines in- creases faster with capacity than does the cost of ditches. Thus, an alfalfa grower taking delivery of a 15 cubic feet per second (c.f.s.) flow would be less likely to benefit from a concrete pipe system than would a grower un- der similar circumstances taking deli- very of 5 c.f.s. The net economy of con- crete pipe systems varies with the value of the land, frequency of irrigation, and the cost of irrigation labor. Thus, it is impossible to set flow limits above which ditches might have some advan- tage over pipe lines. The grower must judge that for himself, possibly with the help of his University of California Farm Advisor and an engineer. The trend, however, is toward larger pipe systems. Cost. A concrete pipe system re- quires a greater investment than do unlined ditches. Economy comes, in time, from the savings in water and labor, and in permanence of instal- lation. Saline conditions. Use of concrete irrigation pipe in saline or alkali soils with a high water table is not recom- mended unless proper reclamation measures are planned. Some precau- tions must also be taken concerning addition of certain fertilizers to water that is to run through concrete pipe. Subject to earthquake damage. Although any risk involved is ex- tremely small, concrete irrigation pipe lines are subject to damage, within a limited area, from movement along earthquake faults. The remoteness of the risk is demonstrated by the fact that, although faults are found throughout California, and although earthquakes are relatively frequent (geologically speaking), the first movement along an earthquake fault known to have caused appreciable damage to concrete irrigation pipe systems occurred on July 21, 1952. There was severe movement along the Bear Mountain fault south of Bakers- field. A few systems immediately over the fault line were so damaged as to be considered a complete loss. In spots, for a distance of 2 to 5 miles on either side of the fault line, some cracking of pipe and stands was observed, the damage decreasing with distance from the fault. Farmers should be able to prevent economic loss from such dam- age, very real but very remote in prob- ability, by some form of insurance. Special repairs required. Usu- ally repairs can be avoided with proper design, installation, and care. But, where repairs are required, special techniques are necessary. NOTE: Figure 18, referred to on page 20 of this circular, is included as a separate, folded supplement, made to scale, for the convenience of the designer. CONCRETE PIPE For IRRIGATION ARTHUR F. PILLSBURY These Are the Different Types of PIPE SYSTEMS When water is distributed in pipe sys- tems in cities, it is necessary only to open a hydrant to get the flow of water desired. Such systems are classified as "closed systems," and are seldom applicable to irrigation because of the much greater flows required by the latter; because it is necessary to use expensive pressure pipe; and because opening or closing hydrants in one part of a system will severely affect flows in another section, thus breaking the constant flow necessary for successful irrigation. Most irrigation systems are classified as "open systems" — periodically, verti- cal, open-top "stands" are placed along a line. These limit pressure, prevent water hammer, and sometimes control pres- sures. Use of such systems requires reg- ulation of gate valves in the lines and the opening and closing of hydrants on a rotation basis. These systems are gen- erally more suitable for irrigation, and permit use of low-cost, plain concrete irrigation pipe. On steeper slopes another type of sys- tem has become increasingly popular in recent years. This is the "semiclosed" system wherein float valves are used in- stead of the overflow stands that are used with the open system on steep slopes. This arrangement has the desirable character- istics of both systems, including the use of the comparatively cheap, plain pipe. Most farm concrete pipe systems, be- cause of flat terrain, will continue to be open systems, although use of the semi- closed type on the steeper slopes should increase. The various components of either open or semiclosed systems are described in this circular. These Are the IRRIGATION STRUCTURES USED Hydrants Hydrants are devices through which water is carried from the pipe line to the land. They regulate the rate of discharge. Their types and characteristics depend upon where the water is delivered — to flooded areas, to ditches, or to furrows. They further vary with the rate at which water is to be applied. Stands Stands on concrete irrigation pipe systems serve a variety of purposes. They relieve high pressures which the pipe lines are not designed to with- stand. They act as surge chambers. Sud- den fluctuations in flow might result in water hammer — almost instantaneous [5] pressure impacts — if excess water could not surge into the stands. Normally, the discharge of a pump goes directly into a stand which dampens the surges and pro- tects the line. (On high-pressure lines operating uphill from a pump, special surge chambers or pressure safety devices are required. These are not discussed here.) They act as air vents. Air often be- comes entrained in the water. This is not desirable because it makes the flow irreg- ular and decreases the capacity of the line. It is essential to have air vents at all high points in a line, where air tends to collect. They can act as diversion struc- tures (gate stands). It is usually desir- able to have laterals branching off a main line. Gate valves mortared to the outlets from a stand regulate the flow into each outlet. They sometimes act as overflow stands to regulate the pressure upstream from the stand. Water must flow over a baffle at a predetermined elevation before it passes on down the system. Thus, the discharge, and consequently, the uni- formity of discharge, from hydrants or into laterals for a distance upstream, are regulated. Difficulty arises with the en- trainment of air in the flow downstream. This can sometimes be minimized by spe- cial design or by substituting a float valve type system. They can also act as float valve stands to regulate the pressure down- stream from the stand. These systems re- verse the usual overflow stand (open system) type of regulation because they admit into the upstream end of the line only as much flow as can be released by the hydrants that are open. Thus, they are classed as semiclosed systems. The overflow stand systems do not hold back any flow, but pass any surplus on down- stream. Neither overflow stands nor float valve stands are required where land is flat. Float valve stands are not yet com- mon on steeper grades because reliable and economical float valves have been on the market only a few years. Since their appearance, however, quite a few over- flow stand systems have been converted to float valve stand systems. They sometimes serve as sand traps, and in this respect are especially useful where wells discharge appreciable amounts of sand. Pump stands should be designed as sand traps. Sand traps may also be useful where water is delivered to pipe systems from unlined ditches. They sometimes act as metering devices, as when a weir or miner's inch plate is installed on top of the baffle of an overflow type stand. Unfortunately, these and similar devices are seldom efficiently and effectively used, except where organ- izations maintain them to deliver water on # toll or allotment basis to individual farmers. To use such devices generally requires periodic measurement of flow (often with some computation and refer- ence to tables) and records of hours run. The most satisfactory meters for farm use are the totalizing propeller-type line i meters, and only those are discussed. Whether stands serve other functions in addition to those of relief, surge dampening, and air venting, is deter- mined by their design. Line Structures A few appliances are sometimes placed right in the pipe line instead of in a stand. Common line structures include gate valves and meters. Line valves have the advantage of easy access for control, and their use is in- creasing. It is unnecessary to climb to the top of the stand to change the setting; however, repair and maintenance may be less convenient. Line meters are of the propeller type, with a totalizing register (as are some of the stand meters used by irrigation dis- tricts) . By simply recording the readings . of the dial before and after irrigation, or at regular intervals through the year, a good record of water application is ob- tained. [6] How to Arrange for INSTALLATION OF A PIPE SYSTEM Most farmers are not in a position to design and do the engineering for their concrete pipe distribution systems, but two methods of contracting for such sys- tems are available to them. Owner-engineered. With this method, the owner employs engineers to make the surveys, plan the system, pro- vide line and grade for the contractor, and inspect the system as it is installed, to see that it conforms to the specifica- tions. The advantage of this method is that the owner can get competitive bids on identical systems from several con- tractors, and can assure himself as to the quality of materials and workmanship. Installer-engineered. When using this method, the owner employs a repu- table installer to make the surveys and design the system. The owner and in- staller review the plans and specifications, which then become a part of the contract. It is essential that such plans specify per- formance in detail, because performance is, in effect, the owner's only safeguard. The standards and specifications in this circular may be used for either owner- or installer-engineered systems. If the system is to be owner-engineered: 1. Make the necessary plans and pro- files showing where pipe lines are to run. (Profiles should be determined after land has been graded. Sometimes it is advan- tageous to irrigate with ditches for a year after new land is brought under cultiva- tion, to insure that grades are satisfactory and that planned rates of flow are ade- quate.) 2. Consult installers regarding avail- ability of the various structures in your locality, and the sizes and quality of appliances. 3. Prepare detailed plans, profiles, and specifications. The contract and specifica- tions on page 00, as well as the standards for the various structures, will help sim- plify this task. Make, size, and quality of all appliances must be specified. Eleva- tions of tops of stands and of crest of overflow stands must be shown on the profiles. 4. Bids are received and a contract is let, specifying date of completion. 5. The owner's representative sets stakes for grade, line, and structures, and inspects the work as it progresses. After completion and testing, the system is ac- cepted. If the owner is certain that his inspection of the installation assures high quality workmanship and materials, it may be specified that the installer is ex- cused from the usual one-year guarantee of performance. When this is done, bid prices should be lower. If the system is to be installer-engineered: 1. Select a reputable installer and go over, with him, the locations of the pipe lines, control structures, and hydrants, and decide on the types and capacities required. 2. The installer makes the surveys and design, and presents the owner with plans, contract, and specifications. These should include information on the type of control structures, capacities of pipe lines, type and capacity of hydrants, and make, size, and quality of accessories for stands and hydrants. If water is to be pumped into the system, the necessary lift must be specified. This is important because while smaller pipe and structures might provide the specified capacities, they would result in increased pumping costs. 3. The sample contract on page 46 may be drawn up, using the specifications and standards for structures given in this circular. When delivery into the proposed system is to be from an open canal, a special inlet structure may be required, details for which are not included in this circular. This structure can be designed by the installer. [7] 4. The contract for construction is then agreed upon. In many instances, the farmer may not have sufficient technical knowledge to determine whether the in- staller adheres to all specification details. He is afforded protection by tests of the system upon completion, by the usual one-year guarantee, and by a few simple observations. He should: A. Inspect the pipe for a smooth and even interior surface; inspect broken faces to see if pipe appears dense, and if gravel fractures rather than coming out whole on such faces; hit the pipe with a hammer to see if it produces a clear, ring- ing sound. B. Watch to see that the laying pro- cedure of the specifications is followed. Observe the cushion under the pipe, the straightness of the pipe, and the depth of cover. See that the initial backfill is made immediately as required, and that the soil used for this initial backfill is moist and not of heavy clay texture. 5. Tests upon completion include one for watertightness. Fill the lines with hydrants closed, then observe the water levels in the stands from time to time. A lowering water level will indicate leakage. Note: Small leaks may tend to seal them- selves; allow the pipe to stand full of water for at least a day before the final test is made. 6. Any trouble that develops after test- ing and acceptance can usually be cor- rected under the one-year guarantee. These Are the DETAILS OF IRRIGATION STRUCTURES On the following pages are shown the various common types of structures used in the systems. These include hydrants, stands, and line structures. Except for a propeller type line meter, no metering structures are shown. (These structures are discussed in California Agricultural Exp. Sta. Bulletin 583, "Measuring Water for Irrigation," and normally will not be installed by farmers but by districts and water companies employing qualified de- signing engineers.) Metal portions of structures, such as gates and valves, are not specified in de- tail. It is expected that the purchaser will inspect the various makes and qualities available and specify accordingly. Steel accessories may be satisfactory with some waters, but will corrode severely with others. Sometimes cast iron, bronze, or brass accessories should be used. Local conditions should be studied before a choice is made. Sometimes, as when the source of water is a canal, special structures, such as screens, will be required. Such structures vary with local conditions and are not standardized enough to be included. Structure A ALFALFA VALVE HYDRANT Purpose: To distribute water into border strips, checks, and large basins. Description: The structure consists of an alfalfa valve set on top of a pipe riser. Valve top should be 1 to 3 inches below ground surface to prevent interference with mowing and to minimize erosion. If land to be irrigated is sometimes planted to row crops, distribution to furrows can be from a stub ditch or from metal "sur- face" pipe, with periodic slide gates along its length, attached to the alfalfa valve through a "portable hydrant." (See Structure H, page 20, for details on sur- face pipe.) Sheet metal stands can also be obtained that fit over the concrete riser [8] with a rubber or other type gasket. Such stands can have connections for surface pipe (the gated pipe for furrow irriga- tion, or the straight surface pipe so that one hydrant can serve two or three border strips) or for plastic pipe (to individual furrows for furrow irrigation). Where, as recommended, entire flow of pipe line can be released from one hydrant at a time, and where available head is low, riser and valve should be the same size as pipe line. An old tire or a short section of large pipe placed around the hydrant and flush with the ground will help mini- mize erosion. If a true alfalfa valve is used with this hydrant it will have a ring outside the disk for attachment of a por- table hydrant. Maximum Design Capacities Recommended Inside Diameter of port Maximum design capacity diameter of riser Usual low head 1 High head 2 inches inches c. f. s. c. f. s. 6 6 0.8 1.6 8 8 1.4 2.8 10 10 2.2 4.4 12 12 3.1 6.3 14 14 4.3 8.6 16 16 5.6 11.2 18 18 7.1 14.2 20 20 8.7 17.5 1 Recommended for minimum erosion with hydraulic gradient 1 ft. above ground. Assu med 0.5 ft. ponding over valve, h =0.5 ft., Q = 0.7A\/2gh where A is the nominal port area, h is the head loss through the valve, and g is the acceleration due to gravity (32.2 ft./sec. 2 ). 2 Can be used where higher pressures are avail- able (hydraulic gradient 2.5 ft. above ground) and precautions are taken to prevent erosion. (Ponding = 0.5 ft., h = 2 ft.) Fig. 1. A typical alfalfa valve hydrant (Structure A). Note machined ring around base of valve, to accommodate "portable hydrant." Structure A. Cross-sectional elevation of typical alfalfa valve hydrant. [9] Fig. 2. Left: Sheet metal device by which flow from a single alfalfa valve hydrant can be directed into either of two checks or border strips. The flow director is designed to fit snugly when pushed down over the hydrant riser. Canvas on the spout helps control erosion. Fig. 3. Center: "Portable hydrant" attached to alfalfa valve hydrant. Gated pipe leads from this structure. This is a common method of converting a flooding irrigation system to a furrow system. Fig. 4. Right: Old tire placed around alfalfa valve hydrant (Structure A) to minimize erosion. Same result could be obtained by installing orchard valve hydrant, but capacity would be considerably lower. Structure B ORCHARD VALVE HYDRANT Purpose: To distribute water into single ditches, large furrows, or into basins, checks, or border strips. Description: These hydrants have an advantage over alfalfa valve hydrants be- cause water flows out of them more quietly, thus minimizing erosion. Their big disadvantage is that the capacity is much lower. They are commonly used in place of alfalfa valve hydrants where erosion is a problem and smaller flows are acceptable. But there is often an ad- vantage in having flows that are larger than the ones these hydrants can provide. Top of pot should be at ground surface except for those of notched design; in the latter, the bottom of the notch is at ground surface. The orchard valve hy- drants can also be converted to the irri- gation of row crops by use of stub ditches or of sheet metal stands that fit over the hydrants (see Structure A). Fig. 5. Left: Modified alfalfa valve installed as an orchard valve hydrant (Structure B). An over- size riser is used, and valve is mortared into the riser. Fig. 6. Right: Variation in design of orchard valve hydrant (Structure B), with overflow notch, which should be at ground level. Advantages are: a larger orchard valve or a modified alfalfa valve can be used; it is high enough to be seen during cultivation; any erosion is concentrated on one side. [10] ot ground surface 0v^0tmj6 feet above ground (h = 2.0 ft.). [ii] Orchard being irrigated with notch design orchard valve hydrants (see fig. 6). Structure C RISER HYDRANT Purpose: To distribute water into fur- rows for systems operating under very low pressures. Description: This structure is simply a riser with two or more slide gate tubes to distribute the water into furrows. Its only advantages over Structure E, the closed pot furrow hydrant, are that gates are on the inside of the riser, resulting in less erosive flow from hydrants, and that it is Maximum Design Capacities Recommended for Slide Gates Diameter Approx. max. capacity inches c. f. s. 1 0.02 IX 0.04 2 0.07 3 0.15 4 0.26 5 0.41 6 0.60 cheaper. Maximum capacity of slide gates is based on the assumption that velocities under about 3 ft. /sec. will not cause ex- cessive erosion. Risers Recommended for Various Sizes and Numbers of Slide Gates Diameter Maximum numbers and sizes of of riser slide gates inches 6 2 gates up to 3 " diam. 8 4 gates up to 1 " diam. ; 2 gates up to 5" diam. 10 4 gates up to 2 " diam. ; 2 gates up to 6 " diam. 12 6 gates up to 1 " diam. ; 4 gates up to 2 " diam. 14 6 gates up to VA" diam.; 4 gates up to 3 " diam. 16 8 gates up to 1 " diam. ; 4 gates up to 4" diam. 12] Structure C. Riser hydrant. This is used where pipe line is always under low pressure, and no orchard valve in riser is necessary. Fig. 8. Installation of riser hydrants (Structure C). Slide gate outlets appear to be too high, and considerable erosion may result. [13] Structure D OPEN POT HYDRANT Purpose: To distribute water into fur- rows, principally with orchard irrigation. Description: The orchard valve regu- lates the flow into the pot, and the slide gates regulate the flow into individual furrows. For best control, the orchard valve is adjusted to keep the water sur- face only an inch or two above the slide gates. Slide gates should be on the inside of the pots, to minimize erosion of the adjacent soil, and at ground surface ele- vation. Size of pot depends upon the num- ber and size of the slide gates to be used. Note: If there is possibility that irri- gation will be changed to broad furrows or narrow strips (possibly 4 to 10 feet wide) for salinity control or for wetting more of the soil volume, set hydrants low so that the slide gates are actually about 3 inches below the surface. Thus, slide gates can be closed and the pot allowed to overflow for greater capacity. This may also affect the size of orchard valve selected. Fig. 9. Open pot hydrant (Structure D). With this installation, the slide gate outlets were placed too far above ground surface, and there was a rather steep slope (3 to 5 per cent) leading away from the hydrant. As a result, there has been considerable erosion, and special precautions are necessary to minimize this. Slide gate outlets should be low. Maximum Design Capacities Recommended For slide gates For orchard valves Diameter Maximum Size (inside Diameter of Usual design of opening design capacity diameter of riser) valve outlet capacity 1 inches c.f.s. inches inches c.f.s. 1 0.02 6 1V2 0.04 IK 0.04 6 2Y 2 0.12 2 0.07 6 VA 0.23 3 0.15 8 5 0.46 4 0.26 10 6 0.67 5 0.41 10 6M 0.78 6 0.60 12 8 1.18 Hydraulic gradient 1 foot above ground surface (Q = 0.6a V g). [14] Pot Sizes Recommended for Various Sizes and Numbers of Slide Gates Inside Maximum numbers and sizes of of pot slide gates inches 6 2 gates up to 3 " diam. 8 4 gates up to 1 " diam. ; 2 gates up to 5 " diam. 10 4 gates up to 2 " diam. ; 2 gates up to 6 " diam. 12 6 gates up to 1 " diam. ; 4 gates up to 2 " diam. 14 6 gates up to l l A" diam.; 4 gates up to 3 " diam. 16 8 gates up to 1 " diam. ; 4 gates up to 4 " diam. Structure D. Open pot hydrant with or- chard valve on top of riser and three slide gate outlets on the pot. The orchard valve is usually adjusted to keep the water level 1 to 3 inches above the slide gate outlets. Such low head simplifies regulation of the latter. Fig. 10. Open pot hydrants for furrow irrigation of citrus. Slide gate outlets appear to be too high. [15] Structure E CAPPED RISER OR POT HYDRANT Purpose: To distribute water into or- chard furrows from low-head pipe lines >n flat grades. Description: The advantages of these structures are : leaves cannot fall into the pots and clog the slide gates, and no orchard valves are required. Disadvan- tages are: less control of the flow, and more erosion of adjacent soil since the slide gates must be on the outside. They are recommended where the hydraulic gradient can be kept within 1 or 2 feet of the ground surface at operating hydrants. Some manufacturers use die-cast, screw type valves in place of the slide gates. These are designed to break the force of the jet and give a quiet, nonerosive flow. See Structure D, page 15, for riser diam- eters (see pot diameters). Maximum Design Capacities Recommended for Slide Gates Diameter of opening Usual design capacity inches c.f.s. 1 0.02 IK 0.04 2 0.07 3 0.15 4 0.26 5 0.41 6 0.60 ' W,A- ' ------ — ■>•-•.•: iv-.vv-.' ■■■>■.■: - Structure E. Capped riser hydrant. Slide gate outlets and concrete cap are mortared to a length of ordinary concrete irrigation pipe. Note: Having slide gates in a short section of pipe with larger diameter than the riser makes the riser hydrant a "capped pot hydrant." [16 Fig. 1 1. Left: Installation of capped pot hydrant (Structure E), showing structure before the cap is mortared on. Fig. 12. Right: Capped pot hydrant after cap has been mortared into place. Fig. 13. Furrow irrigation of citrus with capped riser hydrants (Structure E). Caps keep leaves and other trash from plugging the slide gates. Control is more difficult with this type of structure, and there may be more erosion. [17] Structure F OVERFLOW POT HYDRANT Purpose: To distribute water into fur- rows in contour orchard plantings on steep slopes. Description: These structures combine the functions of the open pot hydrants (Structure D, p. 14) and the overflow stands (Structure R, p. 27). For rela- tively low capacity systems, these are quite satisfactory — regulation is simple, and pressure control excellent. Sometimes the hydrants are reversed — upflow in out- side instead of inside pipe. This reversed type is not recommended because of air entrainment difficulties. The inner riser is of the same size pipe as the pipe line. With use of the design shown here, air entrainment will normally not present any problems. Consult Structure D, page 14, for ca- pacities of slide gates. Principal limita- tion on pot size is the maximum flow in the pipe line. Structure F. Overflow pot hy- drant. This structure simplifies regula- tion of small flows where pipe lines are on relatively steep slopes. Recommended Sizes and Capacities Inside diameter of inner pipe and line Inside diameter of outer pipe Maximum design capacity of pipe line Maximum numbers and sizes of slide gates inches inches c.f.s. 6 16 0.7 4 gates up to V/2" diameter 8 18 1.1 4 gates up to 2 " diameter 10 20 1.4 6 gates up to 2 " diameter 12 24 1.7 8 gates up to 2 " diameter [18] Structure G SWIVEL ARM DISTRIBUTOR HYDRANT Purpose: To distribute small flows of water to furrows. Used in orchards, some- times with row crops. Description: Slide gates are spaced at regular intervals along the galvanized sheet steel or aluminum arms. After fur- rowing, the arms are dropped across the furrows (one slide gate opening to each) . This eliminates handwork necessary to bring furrows up to hydrants. Arms are raised to the vertical and chained to posts, between irrigations. Lengths of arms limit spacing of hydrants to about 25 feet. The system usually consists of: One 1%" st'd. galv. steel pipe riser (extend- ing 2" above ground surface) . One 1%" special die-cast globe valve with swivels for two arms attached (or one 1%" st'd. globe valve plus one 1%" x 1%" x 1%" st'd. galv. tee plus four 1%" st'd. galv. street ells plus necessary bushings and nipples) . Two 10- to 12-ft. lengths of 2" copper bearing galv. downspout or alu- Structure G. One type of combination valve and swivel joints used for swivel arm distributor hydrants. A simple gate valve is often used on the riser, with a tee above and two loose street ells on each side of the tee. minum pipe with 1-inch gates set in at specified intervals. Usual capacity: Of each slide gate = 0.02 c.f .s. Of each hydrant = 0.1 c.f.s. — with provision for 4 feet of water head above ground surface. Fig. 14. Swivel arm distributor hydrants (Structure G) in a young, contoured lemon planting. When not in use, the arms are chained to the posts to prevent damage. Risers should have been shorter so that valves and swivelswould be just above ground surface. Thus water flowing from slide gates in the arms would cause less erosion. [19] Structure H SURFACE PIPE HYDRANT Purpose: To distribute water to furrow- irrigated crops, generally where spacing of hydrants is 25 feet or greater. Used principally for truck and field crops and in orchards of larger trees, such as wal- nut. Note: Some farmers prefer to install alfalfa valve hydrants and to convert these to surface pipe hydrants as needed with a "portable hydrant." This permits rotation of row crops with border strip irrigation. Description: The structure can be one of four types: H-I. A metal "furrow valve" on which are attached connectors for surface pipe running in opposite directions, and which is mortared onto a concrete pipe riser. H-2. A riser hydrant (Structure C, p. 12), but with the slide gates omitted, and in their place, two nipples for attach- ment of the surface pipe. With this type, head in the surface pipe must always be less than the height of water in the hy- drant above the centerline of the nipples. H-3, An open pot hydrant like H-2, but with an orchard valve at the bottom of the Structure H-2. Surface pipe hydrant for low pressure lines. With higher pressure lines, an orchard valve is normally inserted into the riser (Structure H-3). pot (similar to Structure D) . This type is normally preferable (figs. 15, 16). H-4. A capped pot hydrant, but with the slide gates omitted, and in their place two nipples for the attachment of the surface pipe. The pipe itself is often referred to as "gated surface pipe." It has gates in the sides every 20 to 60 inches, as required by the purchaser. It is made of galvanized sheet steel or of aluminum, and normally comes in 20-foot lengths. The simplest type comes with one end crimped so that sections can be driven together (slip joint) and held together by friction. Aluminum pipe with this type of joint is not recommended. However, the pipe also comes with quick couplings, with which aluminum pipe is excellent because of its lightness. The gates of such pipe are adjustable to any opening so that flow in any furrow can be adjusted and equalized where the pressure varies along the gated pipe. Where possible, it is desirable to keep pressure in the pipe low to minimize erosiveness of the jets. Where this is not possible, and savings can be made in pipe size, higher pressures can be utilized. This, however, usually requires baffles or other devices to break up the force of the jet at each gate, which may involve con- siderable handwork and expense. The size of hydrant structure used (normally connecting two reaches of sur- face pipe of 4-, 6-, or 8-inch diameter) depends upon the size of gated pipe re- quired. To determine what size pipe to use, consult the chart (fig. 18) that you will find as a separate, folded supplement accompanying this circular. The height of an open stand should equal the pressure loss (//) in the gated pipe plus about 1 foot freeboard. The following explains how to use the accompanying chart : 1. The purchaser will have decided the length of each line of gated pipe, the maximum discharge per furrow, and the [20] Fig. 1 5. Left: A surface pipe hydrant (Structure H-3) viewed from above, showing the slide gate outlets and the orchard valve. Fig. 16. Right: A line of surface pipe hydrants (Structure H-3). spacing of the furrows. Length (L) is found directly on the chart. Discharge per foot (q) is found by multiplying dis- charge per furrow by 12, and dividing the product by the spacing of the gates in inches. Then, with an understanding of what pressure loss (//) to require, the size of pipe can be determined by laying a straightedge across the chart on the de- sired values of L and q, and reading H for various pipe sizes on the center scale. 2. The pressure losses (H) are approxi- mately the losses that will occur in a gated pipe line along level ground with all gates open and adjusted so that each gate dis- charges at the same rate. This is about Fig. 17. Surface pipe hydrant (Structure H-2) with gated surface pipe, shown here as used for irrigation of citrus. [21] one third the loss that would occur if the full flow were discharged at the end of the line. If water is discharging only along a portion of the line, the losses will be increased (three times the loss for the portion with full flow) . 3. The velocity of water issuing from a jet depends upon the pressure in the pipe upstream from the jet. So that the jet of water at each gate will have low velocity, it is desirable that pressure be low in the pipe. If pressure loss through the pipe is high, at least some jets — those at the up- stream end — will have high velocity, and soil erosion will result. It is generally de- sirable that pressures be kept as low as possible. This is achieved by use of the control valve on the hydrant. With the nearly perfect installation, the pressure loss in the gated line will be about 1 foot (H = 1 ft.) . Sometimes, in the interest of economy, a smaller pipe must be used wherein the jets are erosive, but damage is prevented by placing sacks, rocks, boards, or the like in the furrow where they will break the force of the jet and prevent erosion. Or attachments for the pipe can be made that will break the force of the jet. Then the pressure loss in the line can be increased to 2, 5, or up to 10 feet. Generally the concrete pipe line, from which the gated surface pipe is served, should not be under higher pres- sure than would be caused by a pressure loss of 10 feet in the gated line. 4. First Example : Hydrants are to be placed 120 feet apart in a field with fur- rows spaced 30 inches apart. Length of each gated line will then be 60 feet. Maxi- mum discharge per furrow will be 0.05 c.f.s. Discharge per foot will be 12/30 x 0.05 = 0.02 c.f.s. Pressure loss would be slightly more than 4 feet in a 4-inch line and less than 1 foot in a 6-inch line. 5. Second Example: There is a con- crete pipe line down the center of a field parallel to the furrows. At 300-foot inter- vals there are surface pipe hydrants. Gated surface pipe is to run along level ground from these hydrants for distances of 660 feet. Spacing of furrows is 40 inches, and maximum rate of flow is 0.01 c.f.s. per furrow, with one third of the furrows in operation at one time. Solution: The condition under which maximum pressures will be created oc- curs where gates are discharging 0.01 c.f.s. at the far end of the line. Thus, there will be full flow for 440 feet. In the last 220 feet, the discharge per foot will be 12/40 x 0.01 = 0.003 c.f.s. Going to the chart (discharge per foot = 0.003 c.f.s., length = 220 ft.) we find that use of a 6- inch gated pipe appears reasonable — the pressure loss in the operating portion is just under 1 foot. Next, we can find what the loss would be in the 440 feet of pipe serving as a main. Total flow would be 0.003 x 220 = 0.66 c.f.s. "Flow per foot" equivalent would be 0.66/440 = 0.0015 c.f.s. Going to the chart we find the loss, for 6-inch pipe, to be about 1.7 feet. We require full flow to the end of the line, however, so we must multiply by 3. Total loss in the "main" part of the line, then, is about 5 feet. Total loss in the whole line would be about 6 feet. Also, there will be loss in the concrete pipe riser and in the surface pipe hydrant. The hy- draulic gradient of the concrete pipe line, therefore, might well be about 7 feet above ground surface. Structure L LINE GATE VALVE Purpose: To shut off or control flow without having the gate valve in a stand. Line gate valves are most useful where stands are high because they make it un- necessary to climb to the top of the stand to turn the valve. Also, gate valves per- mit the use of small-diameter, special capped vent stands instead of large gate stands. (See Structure V, p. 30.) The present trend is toward use of line gate valves with adjacent capped vent stands. [22] Structure L. Two views of typical line gate valve for use on a concrete pipe line. Description: This structure is simply a gate valve with hub ends that are mor- tared directly into the pipe line. Size, make, and quality should be specified. The turning screw or hand wheel of the valve is on an extension rod and is made accessible by placing a length of concrete pipe in position over the valve as backfill proceeds. Quick closing valves should not be used. Losses: Friction losses in wide open gate valves are low, and frequently can be ignored. Following are approximations of wide open losses in terms of "equiva- lent lengths of straight pipe in feet" that can be used where needed: Pipe and valve Equiv. length of size straight pipe inches feet 6 4 3 5 10 6 12 7 14 8 16 9 13 11 20 12 24 14 Since such losses are small, and since the cost of gate valves increases greatly with size, the question is often asked whether a valve somewhat smaller than the pipe can be used. This is best answered by computing the approximate loss from the above and from the pipe friction loss table (p. 40). Example: In a 12-inch line to carry 4 c.f.o., it is desired to install a 10-inch gate valve. The friction loss would be 6 ft. of pipe (from above) x 31.6/1000 (from pipe friction loss table, for 10-inch pipe carrying 4 c.f.s.) = approx. 0.2 ft. Fig. 19. A typical line gate valve (Structure L). [23] Structure M LINE METER Purpose: To meter the flow. A totalizing register mounted on top of the meter indi- cates the total quantity of water that has passed through the meter. The difference between readings before and after an irrigation permits computation of the total amount applied in that irrigation. By knowing the time interval between the two readings, rate of flow can be com- puted. Description: These meters are of the propeller type, most suitable because of low friction loss and because their dis- advantage — failure to register at very low flows — is not important in irrigation where flow is relatively constant. The meters are mortared directly into the pipe line, and a length of pipe over the register permits reading the meter. Extensions to raise the register to or near the surface are available if desired to facilitate read- ing. These meters should not be used on any pipe lines which might carry trash that will stop the propeller. The meters must be completely submerged at all times (pipe must not flow part full) . Structure O GATE STAND Purpose: To prevent high pressure, act as air vents and surge chambers, and con- trol the flow by means of the one or more gate valves they contain. They may also serve as stands for pumps to discharge into, and/or as sand traps. Where used: Gate stands are used to regulate the flow into laterals, or where, on a single line, it is desirable to create upstream pressure so that water will flow from hydrants at that point. This is done by partially closing the gate valve — or by closing it all the way if irrigation from the downstream line has been completed. The present trend is to substitute line gate valves and capped vents for gate stands, especially where a high stand would be required. This practice is not desirable where the structure must also serve as a sand trap. Structure M. A typical line meter. It must be installed so that pipe is completely full of water at all times. Structure O. Sectional elevation of a simple gate stand. Gates are usually set on the outlets from stands. Thus pressure of water in the stand tends to close the gate rather than hold it open. [24 Diameter of stand: This should be large enough to accommodate the gate valves and to permit getting down into the stands to work on the gates. Specify: Inside diameter of stand, acces- sories required, and any additional re- quirements of stand, such as to serve as a pump stand (Structure P) and/or sand trap (Structure U). Gate valves are of two general types: the screw lift (some with rising, and some with nonrising stems) , and the slide type with a cam device for locking in any position. The screw type is easier to regu- late; the slide type may be cheaper. There is less possibility of heavy surges or water hammer with the screw type because it cannot be closed as suddenly. The pur- chaser should satisfy himself as to the quality and size of accessories he desires, and so specify. Box stands instead of pipe stands are sometimes utilized for gate stands. Speci- fications for the former vary with local conditions, and are not included herein. Recommended Sizes Inside diameter of pipe line Inside diameter of stands With one gate With 2 or 3 gates inches 6 to 10 12 inches 30 30 30 30 30 42 48 inches 30 36 42 42 48 54 60 14 16 18 20 24 Structure P PUMP STAND Purpose: To convey the flow of the pump into the concrete pipe system and to serve functions of other stands. Description: The pump discharge nor- mally flows into such a stand above the ground surface elevation. If this elevation is below the hydraulic gradient of the pipe line, a flap valve should be placed at the end of the pump discharge line in the stand. Thus, water in the pipe line can- Structure P. Pump setup. Sectional elevation of a simple pump. The Dayton type coupling and oakum packing absorb vibration, which prevents cracking of the stand. Where the pump discharge pipe enters below the hydraulic gradient, a flap valve prevents backflow through pump when pump is off. [25] not flow back into the well when the pump is shut off. Normally, a metal pipe runs from the pump to the stand, through the wall of the stand, and is mortared into place. To keep pump vibration from cracking the stand, a flexible coupling should be placed on the pump discharge pipe. A straight reach of pipe, at least 20 diameters in length, facilitates metering of the flow by pump companies and power companies. (Pump tests are often a free service of power companies.) If pump stands must be high, they are sometimes capped (fig. 21). The capped design should never be used where the well has any tendency to pump sand. Since wells often discharge some sand, the pump stand may also be made to serve as a sand trap (Structure U) . Diameter: Use 30-inch pipe or larger (as required by other functions of stand) . Specify: Diameter of stand, accessories required, and any other functions the stand is to serve. Fig. 20. Left: Typical pump and gate stand (Structures P and O). Pump discharge is above hydraulic gradient in stand to prevent backflow when pump is shut off. Fig. 21. Right: (A) capped pump stand (Structure P); (B) line valve; (C) capped vent stand. Gate valves are used on the pump discharge pipe wherever a considerable amount of water might flow back into the well when the pump is off. (Hydraulic gradient is above elevation of pump discharge and of other pumps on the system.) Fig. 22. Typical box gate stand (Structure O). Such structures are ex- cellent. Relative cost, according to facilities of individual installer, deter- mines the type used. [26] Structure R OVERFLOW STAND Purpose: To function both as a check and a drop structure in addition to the usual functions of a stand. As a check structure, it regulates pressures to main- tain constant upstream flow out of hy- drants and/or into laterals. As a drop structure, it creates a drop in the hy- draulic gradient, thus limiting pipe line pressures. This structure is not required on flat areas or very slight slopes. Note: Overflow stands are often con- structed without a gate valve between the upstream and downstream portions of the stand. Because of the danger that surge will be created by the entrainment of air in the downstream portion, construction of stands without gate valves is not recom- mended, and such structures are neither illustrated nor described herein. The gate valve is normally open. When diversion or discharge of hydrants immediately up- stream is desired, it is closed sufficiently that head upstream is about at the over- flow crest, but little or no overflow is tak- ing place. Description: The structure is, in effect, two stands with connections between them at the pipe line elevation, where the gate valve is installed, and at the elevation of the overpour lip. The upstream stand is essentially a gate stand. (See Structure for dimensions.) The downstream stand is normally of the same diameter as the pipe line. Larger size for the down- stream stand would help minimize air en- trainment, but since there is no assurance that surging could be prevented, larger downstream stands are not recommended. Fig. 23. Overflow stand (Structure R) controlling pressure in upstream hydrants. for Structure T FLOAT VALVE STAND Purpose: A series of such stands are ad- vantageous on steep slopes to form a semiclosed system. Each valve controls pressure in the reach of pipe immediately downstream from it, and such valves re- lease into the stand only as much water as hydrants farther downstream are open to take. Description: The float valve is attached to the end of the pipe through which water enters the stand. The valve opens and closes so as to maintain a nearly con- stant level of water in the stand which is directly connected to the line or lines through which water flows downstream. The downstream pressure is determined by the water surface elevation, and hence by the setting of the float. If such float valves are designed to prevent almost all fluctuation in the water surface elevation, there is a tendency for the valve to "hunt" — a partial opening and closing [27] ;-;'; i.vi Structure T. Sectional elevation of part of a float valve stand, showing installation of an open, single disk type float valve. Fig. 24. Installation of a float valve of th< double disk, balanced type. occurs that produces a rhythmic variation in flow. This tendency is accentuated when float valves are in series. Hunting is prevented by providing for a water sur- face elevation fluctuation in the stand, between valve-open and valve-closed posi- tions, of 6 inches to 1 foot, and on other adjustments to the reaction of the float. Thus, the float should be tall relative to its diameter, or there should be linkage between valve and float. The purchaser should satisfy himself as to the desir- ability of the valve he selects. One type might have the advantage of readily pass- ing any chance trash in the line; another might be "balanced" (so constructed that the float volume is independent of the upstream water pressure) ; and another might or might not be designed for com- plete shut-off. Sometimes complete shut- off is desirable to eliminate the need for supplemental gate valves where a portion of a system will be out of service while the remainder is functioning. Generally, stands 30 inches in diameter are required, but practices have not become sufficiently standardized to enable us to set up rigid specifications as to size or design. Gen- erally, about 2-foot freeboard is desired. Where the valves are not "balanced" the float must counterbalance the head against the disk. Size selection: The size of float valve required depends upon the head loss Flow in c.f.s. Through Wide Open Float Valves with Head Losses Indicated Type and size Head loss in feet of water 0.5 l 2 5 10 20 Double disk (balanced) type: 4 inch c.f.s. 0.22 0.52 0.98 0.34 0.47 1.28 c.f.s. 0.31 0.74 1.39 0.48 0.66 1.80 c.f.s. 0.43 1.03 1.97 0.68 0.93 2.55 c.f.s. 0.69 1.66 3.10 1.08 1.49 4.05 c.f.s. 0.97 2.32 4.40 1.53 2.10 5.75 c.f.s. 1.39 3.30 6.25 2.18 3.00 8.15 6 inch 8 inch Single disk (open) type: 4 inch 5 inch 8 inch [28] available, and the friction loss in the valve when wide open under full flow. Table on page 28 shows rate of flow through the various valves now on the market for farm systems, with valves at wide open position, for various head losses. Structure U SAND TRAPS Purpose: To permit the settling out of sand and other suspended material in the water. This keeps such material from settling out in the pipe line where it re- duces capacity. Sand traps are suitable for use where the water is delivered into the system by a pump. The large box structures, generally used when water diverted from a canal carries either sus- pended or bed material, are not discussed here. (These will vary with local condi- tions and will frequently be combined sand traps and screens.) Description: The structure is simply a stand — commonly a pump stand — with sufficient cross-section to insure low velocities. Space is provided at the bot- tom, below the inverts of the outlet pipes, for the collection of sand, which is peri- odically bailed out. These structures do not remove all suspended matter, and sometimes it is desirable to have the sec- ond stand downstream on the system also serve as a sand trap. Recommended speci- fications for all sand traps are given on the following page. Structure U. Sand trap. This structure is commonly a pump stand with sufficient cross section to insure low velocities. Sand collects in space below the inverts of the outlet pipes, and is periodically bailed out. Inlet Optional hardware cloth lauers Space fot- sancl to collect - -O.v.o.. -O Outlet [29] A. Vertical offset of inlet and outlet (pref- erably up to 2 times the pipe line diam- eter) . B. About 2 feet inside depth of stand be- low outlet invert elevation. C. Inside diameter such that the average vertical velocity does not exceed about % ft./sec., and diameter never less than 30 inches. Three horizontal layers of %" to %" hardware cloth, possibly with %" to 1" separations, just below the inlet will make these structures more effective by limit- ing the "piping" through of the flow. Recommended Diameters of Sand Traps Maximum flow Diameter c.f.s. inches 0.5 30 1.0 30 1.5 33 2 39 3 48 5 60 Structure V VENT STAND Purpose: To serve as an air vent, and to prevent high pressures. Description: Vent stands are used at every high point in a line, at increases in down grade from a relatively flat slope, and at the end of each line. Any of the stands previously illustrated and dis- cussed also serve as vent stands, thus minimizing the number required. Where small amounts of air are en- Structure V-l. Straight vent stand. Top of stand is normally about 2 feet above maximum hydraulic gradient, and not less than 4 feet above ground surface. Where feasible, this is the most effective vent and surge chamber. Stand is same diameter as pipe line. '^foM&^WNJSrmU i MiferP AIR POCKET TO ABSORB SURGE • THE MORE VOLUME IN THE POCKET. THE MORE SURGE ABSORBED 'i . A " ' a 'J"'o '*■ ° °'» ° ••" ■ » '■ *■ o ■• ' : c r-* I klS Structure V-2. Sectional elevation of capped vent stand. The large riser should have the same diameter as the pipe line, and its height should be twice the diameter, or more. The small pipe line may extend down into the large riser to create an air pocket that will absorb surge. [30] Fig. 25. Left: Capped vent stand (Structure V-2). Steel pipe is used here for the constricted por- tion. Sometimes sheet metal pipe is used where the water has little tendency to corrode. With more corrosive waters, asbestos-cement pipe is used. Note turning wheel for line gate valve (Structure L) immediately to the left of the vent stand. Fig. 26. Right: A constricted vent stand (Structure V-3) made of 6-inch concrete sewer pipe. This pipe differs from concrete irrigation pipe because it has bell-and-spigot joints. Such pipe is superior to the irrigation pipe for stands up to 12 inches in diameter because the temperature and moisture changes occurring in exposed pipe above ground surface make irrigation pipe susceptible to leakage. An alfalfa valve hydrant (Structure A) is at base of vent stand. trained in the water, such as at the en- trance to a pipe line from a canal, a con- stricted vent placed less than 5 feet be- yond the entrance to the pipe line often serves effectively to release such air. V- J. Straight vent stand. The diam- eter of this type is the same as the di- ameter of the pipe line. It is placed after the line is laid, on top of a hole cut into the line. It should rise to an elevation at least 2 feet above the maximum hydraulic gradient. An anchor should be cast around the pipe under the stand. This type is usual on low head systems. V-2. Capped vent stand. These are common where gradients are more than about 8 feet above ground surface. The bottom portion of this vent stand is the same as the V-l, the stand pipe being the same diameter as the pipe line. However, at or near the ground surface it is capped over, and a small-diameter pipe extends through the cap to an elevation 2 feet above the maximum hydraulic gradient. The cap should have a minimum height of 2 diameters over the crown of the pipe line. The small pipe may be steel, sheet steel, or asbestos-cement, and the type and size to be used should be specified. Guying may be desirable. This will de- pend upon the size, height, and type of pipe used. Following are the recommen- dations for size of pipe above the cap: Pipe line diameter Suggested pipe dia. above cap inches up to 8 10 to 14 16 to 24 inches lto2 2 to 4 4 to 6 [31] Fig. 27. An air-release valve vent stand (Structure V-4). The optional gate valve imme- diately above the concrete portion permits shut- ting off the air-release valve in case it sticks at open position. Air-release valve is above the gate valve. The elbow on top directs the jet of water away from the irrigator if the valve should stick. Although not customary practice, the ex- tension of the small pipe down into the larger riser is recommended. Air will be trapped in the space between the two pipes and, being compressible, will ab- sorb pressure waves (act as a surge cham- ber). V-3. Constricted vent stand, A com- mon type of vent stand is simply a small- diameter pipe (such as that above the cap on the V-2) straight up from the pipe line. Air removal with such vents is in- efficient and there is less relief for surge (depending on size). Therefore, the con- stricted vent stand is not recommended for general use, but may satisfactorily serve to release air from the ends of dis- tributing laterals during the filling of such laterals. V-4. Air release valve vent stand: Below the air release valve this structure is similar to V-2. It is used where an ex- cessively high vent pipe would otherwise be required. When air enters the valve, a floating ball drops, opening the valve until the water level again comes up. Sometimes the valves stick — some makes probably more than others. A gate valve below the air release valve, and an ell above, make it easy for the irrigator to correct the difficulty. Elements to Consider in PLANNING THE SYSTEM Because of great variations in soil char- acteristics, topography, crop rooting and growth habits, climate, and water avail- ability, the methods and rates of water application also vary widely. In order to adapt a concrete pipe system to a partic- ular piece of land, the designer must first know these three things: 1. Hydrant capacity and type. Some- times this is limited not by the crop, but by the rate at which water is available. The designer should know the maximum rates at which water is to be delivered, and whether it goes to border strips, checks, furrows, etc. 2. Hydrant spacing. The designer will determine how far apart to space the hy- drants by studying the nature of the crop, the soil, and the cross-slope. 3. Pipe line spacing. The designer must know the length of run, as this de- termines pipe line spacing. Efficiency of irrigation (uniformity of application along the run) does not necessarily in- crease with decreasing length of run pro- vided rates of flow are adequate. Inefficient distribution systems often result not so much from poor pipe design and installation as from poor adaptation to the land — poor selection in the three [32] items above. Failure to provide adequate hydrant capacity is the most common fault. These factors are discussed following a description of the hydraulic and other units that must be used. Rate of flow is a measure of volume of water per unit time. The commonest unit used is cubic feet per second (c.f.s.) . Other common units are gallons per minute (g.p.m.) and miner's inches (M.I.) . The miner's inch is unsatisfactory because it represents different rates of flow, not only in other states, but also in different parts of California. Gallons per minute is a convenient unit with pump irrigation, but is less convenient to con- vert to depth of application. Cubic feet per second is therefore used throughout this circular. The following conversion factors can be used to change other units to c.f.s. : Divide gallons per minute (g.p.m.) by 450 (actually, by 448.83, but 450 is ac- curate enough). Divide the customary southern Cali- fornia miner's inches by 50. Divide the statute northern California miner's inches by 40. (Note: Still other factors would be used in other states.) Depth of application refers to the depth of water applied, in feet or inches, to the land. It is sometimes referred to as volume of water per unit area, which is the same thing. It is frequently necessary to convert flow rate (q) to depth of appli- cation or volume. Convenient conversion factors are given below. Slope of the land is important in plan- ning the system, and the units involved must be understood. Slope is referred to in several ways: As a ratio. This is the feet vertical rise or fall of the land per foot horizontal distance. It is a true ratio, and no units are used. As a percentage. This is the feet ver- tical rise or fall of the land per 100 feet horizontal distance. As "feet per 1 00 feet." This is the same as per cent slope. As "feet per mile." The feet vertical rise or fall per mile (5,280 feet) horizon- tal distance. Comparison: A parcel of land slopes 0.2 feet vertical per 100 feet horizontal. This is: As a ratio, slope = 0.002 As per cent, slope = 0.2 per cent As feet per 100, slope = 0.2 feet per 100 feet As feet per mile, slope = 10.56 feet per mile Slope is expressed as a ratio herein. These are desirable hydrant types and capacities: For flood irrigation, either the al- falfa valve hydrant or the orchard valve hydrant is used. The former provides the greater rates of flow, the latter provides a neater hydrant and, with some soils, less erosion. Rate of flow is often need- lessly sacrificed by use of the orchard valve hydrant. Flood irrigation includes the border strip, the contour check, the rectangular check, and the basin methods. Large strips, checks, or basins usually result in economical farming operations. Therefore, it is recommended with flood irrigation that hydrants for each strip, CONVERSION FACTORS 1 acre foot (volume) = 12 acre inches (volume) 1 acre foot (volume) = 43,560 cubic feet (volume) Rate of flow {q) in c.f.s. x hours = acre inches (approx.) Rate of flow (q) in c.f.s. x hours . = inches depth (acre inches per acre) (approx. acres irrigated [33 check, or other unit be of sufficient size to take the entire flow of the pipe system. For a given soil and crop, the permissible size of these strips, checks, and basins depends upon the flow that can be put into each. Generally speaking, there is a desirable trend away from furrows and toward flood irrigation for most crops except row crops, crops on steep slopes or on soils with profile development, and citrus (ex- cept possibly in desert areas). Types of plantings on which flooding methods could well be used more extensively in- clude vineyards, deciduous fruits, nuts, dates, and desert citrus orchards. Many vineyards, in particular, can be irrigated with strips, checks, and basins, the width of which may include several vine rows. For established farms there are simple field techniques that are used to determine the proper size of each flooded unit. The local Farm Advisor can be of help in plan- ning such tests. Otherwise, it may be nec- essary to rely on empirical computations utilizing the constant R in the relationship R = q/a, where R = time rate of water application to strip, check, or basin. q = rate at which water is applied to the strip, check, or basin, in c.f.s. a = area of the strip, check, or basin, in acres. By using the table of values of R it is possible to compute either (1) the rate of flow of each hydrant (q = Ra) where the size has been fixed, or (2) the size of each strip, check, or basin (a = q/R) where the maximum hydrant discharge is fixed. Thus, if R = 5 c.f.s./ac., and a = 0.5 ac, q would equal 2.5 c.f.s.; or if R = 5 and q = 3, a would equal 3/5 ac. (0.6 ac, or a strip about 40 x 660 feet). (See table at bottom of page.) With furrow irrigation, the aim is to wet downward and, to a variable extent, sub the water into the ridges. The latter requires a rather adequate flow of water to maintain considerable depth in the fur- rows, but in any case a good flow should be provided to attain high irrigation efficiency. There is seldom reason to pro- vide for a flow of less than 0.02 c.f.s. per furrow, even though the rate of flow in furrows does range from about 0.001 to 0.2 c.f.s. in extremes. Normal provision for maximum furrow flow should be in the range of 0.02 to 0.1 c.f.s., depending on permeability of soil, erodability, slope, size of furrow, and type of planting. There should be no significant differ- ence between costs of hydrants that pro- vide the recommended flows and those of hydrants with lower flow provision. Usual Time Rates (R) of Water Application for Flooding (The figures given will vary somewhat with the cost of water, value of crop, and frequency of irrigation. R will be smaller if slope exceeds 1 per cent.) Soil characteristics Coarse, sandy soils (most permeable) Sandy loam soils Medium silt loam soils Clay loam soils Heavy clay soils (least permeable) . . . [34 Deep- rooted crops (4 to 6 ft.) c.f.s./ac. 15 8 4 2 1.5 Medium- rooted crops (2 to 4 ft.) c.f.s./ac. 20 10 5 3 2 Shallow rooted crops (0 to 2 ft.) c.f.s./ac. 30 15 8 5 3 These are desirable hydrant spacings: In furrow-irrigated orchards, and in some vineyards, hydrant spacing is regulated by tree spacing. Putting hy- drants in line with a row of trees helps keep them away from traffic, and 1 to 4 furrows on either side of the row can be readily served by each hydrant. Common spacings are 18 to 25 feet. With furrow-irrigated row crops, the preferred practice is to plan hydrant spacing for flood irrigation since in most areas rotation is desirable — rotating the row crops periodically with alfalfa, per- manent pasture, or other forage crops. Almost any reasonable spacing for flood irrigation can be adapted to furrow irri- gation with spud ditches and a system of furrow tubes or furrow siphons. Gated pipe may also be used for such adapta- tion, with some saving of water. With flood irrigation, spacing of hydrants is normally regulated by cross slope — slope parallel to pipe line. Width of border strips, contour checks, and ba- sins is normally set to give not over 0.2 foot elevation difference. Thus, if the cross slope is 0.005, the border strips, etc., will be 40 feet wide, and the hydrants will be spaced every 40 or 80 feet apart. (There may be some inconvenience in having only one hydrant for two border strips.) A few growers prefer smaller hydrants, and have two or more for each flooded unit. This requires a greater in- vestment, but smaller flows may result in somewhat less erosion and easier control. These are desirable pipe line spacings: Pipe line spacings may range, in ex- tremes, anywhere between 100 feet and 2,640 feet (1/2 mile). With flood irri- gation, pipe line spacing (length of run) most commonly ranges between 1/8 mile (660 feet) and 1/4 mile (1,320 feet) if slopes are moderate (less than 0.005) and uniform, and if adequate flows of water are available. Attention is called to the relation R = q/a, previously explained (p. 34) , which may fix pipe line spacing. With furrow irrigation, the length of run most commonly varies between 220 feet and 660 feet. With adequate water flows and moderate slopes, there is seldom need for shorter runs. Where sub- bing is practiced (vegetables), runs are shortest, and where deep irrigation is de- sired (field crops, orchards, vineyards), runs are longest. It is important to remember that ade- quate flow and moderate, uniform slope are more important in attaining good ir- rigation efficiency than are short runs. Most poor distribution along the length of the run results from too small a flow rather than too long a run — rate of flow may be limited either by available supply or, more commonly, by too steep a slope. Slope may influence design Since slope bears so important a rela- tionship to design of the irrigation dis- tribution system, general practices and recommendations are summarized below. Normally, slope in the direction of run varies from zero to about 0.01 for either furrow or flood irrigation on the usual relatively flat terrain. With furrow irrigation, where small flows are preferred and where the princi- pal object is to get 3 to 6 feet penetration of the water into the soil, slopes range from about 0.005 to about 0.01. More gentle slopes are commonly preferred for most crops, and the general recommen- dation would be for grades between zero and 0.003. On steep slopes, and land, that cannot be leveled because of profile development, the direction of furrows follows the con- tour of the land. The furrows are run on a contour grade (often around a side hill) . Because there is danger that water may break out of the furrows and flow down the slope, grades are usually steeper and the flows small. Grades varying from 0.01 [35] to 0.03 are recommended, depending on the slopes involved and the nature of the soil. Erosion often limits the rate at which water can be run down a furrow, and slope is of prime importance in determin- ing the susceptibility of a soil to erosion. Depending upon how readily a soil is eroded, the following may be taken as rough limits of the allowable flow per fur- row. Slope of land Range in max. flow to avoid along furrow erosion, depending on soil feet per foot C./.5. 0.001 0.1 to 0.2 0.002 0.06 to 0.1 0.005 0.02 to 0.05 0.01 0.01 to 0.02 The slopes for flood irrigation are simi- lar to those for furrow irrigation. Flood- ing methods can be adapted to all types of topography. Where it is feasible to level land, the more gentle slopes are prefer- able — generally less than 0.003. Slopes from zero to 0.003 are preferred — often the flatter, the better with precise level- ing — although efficient irrigation can be attained on slopes up to at least 0.006. On low value development, or where leveling is not feasible, slopes up to 0.06 have been used successfully, but not with high effi- ciency. The above refers to slopes in the direction of irrigation run. Previous ref- erence was made to limitations on cross slope for flood irrigation, and it is not a big factor with furrow irrigation. Hydraulic gradient. Water is carried in pipe lines under a small but positive pressure. At stands, that pressure causes the water to seek and maintain a certain level or height, and that level is the elevation of the hydraulic gradient at that point in the line. On a profile, the hydraulic gradient is a line connecting the water surfaces in the vari- ous stands. Since there is "friction loss" of energy in water flowing through a pipe, the hydraulic gradient always slopes down in the direction of flow. The slope steepens with increase in flow, and it steepens with each decrease in pipe size for a given flow. The hydraulic gradient for an 18-inch pipe line, 2,650 feet long, with discharge of 3 c.f.s. at the far hy- drant, is shown in Figure 28. The vertical drop of the hydraulic gradient in 1,000 feet horizontal corresponds to the friction loss per 1,000 feet shown in the table on page 40. Note that the hydraulic gradient is rather independent of the actual eleva- tion of the pipe line — except, of course, that the hydraulic gradient should not drop below the pipe line. If the hydraulic gradient at any hydrant is at the ground surface, the water can rise to that elevation but cannot flow out. The gradient must be high enough to overcome friction losses through the riser and hydrant, and to flood the ground sur- face for a depth of from 2 to 6 inches. High pressures make control difficult. Therefore, a common standard is to have the hydraulic gradient about 1 or 2 feet above the ground surface at the hydrant where discharge is taking place. The pressures at upstream closed hydrants, or upstream hydrants where only partial flow is being discharged, are of necessity usually somewhat higher. Some types of hydrants often require a higher head, as indicated in the details on hydrants. The hydraulic gradient shown in Fig- ure 28 applies only when the entire flow is discharged at one hydrant. Further, it is only approximate because minor losses, such as those caused by bends in the pipe line, and losses at structures, will have some effect upon it. However, with these pipe lines, such losses are small and can be ignored. The hydraulic gradient for the same 3 c.f.s. discharge at any other hydrant (as to 13 + 90) is parallel to the gradient to 26 + 50, as shown in Figure 28. Limiting heights of stands. As shown in Figure 28 at station + 00 it is sometimes necessary to have relatively [36 1 I ( t il l*" ..OI ..9i .91 .91 ..91 .,91 .91 ,.91 ,.91 ..91 ,91 ..9i ,.9l ,.91 ..91 0..91 0..0G ..91 .91 ..91 ,.91 ,.91 .91 ..91 0. .91 .91 .91 ..91 .91 ..9) IA V V V v V V V V V V V 3. n v v v V V V V V V V V V IA V V V V V V V 09* 9?. 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IO05IOMN © © rH ^" t> coq i>"^oq dcodoocd CO CO«tf Tt» © q ©©cm • © © co i> © t- © © rH rH * © rH rH rH rH rH The pressure of water in concrete pipe creates tensile stress in the shell. External loading, from backfilled earth and traffic over the pipe, creates both compressive and tensile stresses. Therefore, plain con- crete irrigation pipe, which contains no reinforcing, must be carefully designed and placed so that tensile stresses are never excessive. One might ask — why not reinforce concrete irrigation pipe with steel as a precaution against failure? Such pipe is made, as is another type made by centrifugal and by vibrating processes that result in an especially dense and strong product. These types are excellent, but at present are too costly for the usual farm distribution systems. They are sometimes used on farms for special booster lines. Since design of such high-pressure lines requires special engi- neering services, they are not discussed here. Concrete irrigation pipe is customarily fabricated by troweling or tamping ma- chines that produce it quickly, cheaply, and in quantity. Using this pipe, systems can be designed which operate simply and with perfect satisfaction. They often successfully withstand considerable abuse in operation. These facts explain the popularity of concrete pipe, but knowl- edge of its limitations is necessary to ob- tain the greatest possible value from the systems. How to avoid failure. Most systems are used year after year without giving trouble. But there are always a few fail- ures, generally of the following types: 1. Development of longitudinal cracks in the pipe, principally in the top or in both top and bottom. 2. Telescoping of sections. 3. Pushing of the pipe into the stands. 4. Development of circumferential cracks. 5. Deterioration of the concrete. 6. Surging or intermittent flow of water. The first four types of failure are closely related. The cause of most failures (types 1, 2, and 3) , and the prevention of some (type 4) stem from the fact that concrete expands when wet, and contracts when drying. Concrete also is affected by temperature: it expands when heated, and contracts when cooled. Circumferential cracks are caused by a drop in water or soil temperatures, or by drying out of the pipe. The primary cause is low water temperature of surface supplies in winter and early spring. Well waters seldom give trouble. Such cracks may be partially prevented by prestress- ing the pipe longitudinally. Fortunately, this prestressing tends to occur auto- matically when the pipe, which is laid dry, expands on becoming wet. Longi- tudinal stress from wetting expansion does not normally remain high for more than a few months to a year, but it con- tinues to offer some protection. The axial stress set up in pipe by the natural restraint of longitudinal expan- sion is a partial cause of longitudinal ripping, and also the cause of telescoping and pushing of pipe into structures. The longitudinal rips normally occur within a few days to a week after pipe is laid. Other wetting stresses can occur as a re- sult of change in moisture gradient through a pipe wall, or from a wetter condition around the bottom than around the top of a pipe. Also, stresses can de- velop as a result of air circulation through a pipe, causing thermal expansion or contraction. Ripping results from a com- bination of circumferential stresses and longitudinal restraint. The solution to the problem of occasional failures lies not in eliminating wetting expansion, but in keeping it from becoming excessive, and in minimizing moisture gradients around the shell. Failure from the above causes can be avoided by proper laying procedure, as outlined in the laying specifications (p. 49) . First, it involves the use of moist soil for the initial backfill after laying the pipe. This procedure minimizes the cir- cumferential moisture stresses and takes 42 any excessive peak from longitudinal stress. Another recommended, but seldom practiced, precaution is to minimize air i circulation through a line when laying pipe and when the line is not in use. On flat grades this is automatically accom- plished because water stands in the lines. On steeper grades the same thing can be accomplished by having a semiclosed system; by keeping hydrants closed and having covers over the stands; and/or by designing overflow stands so that the pipe is always submerged for a short dis- tance above such stands. Covers should be free to lift up, like a flap valve, if pres- sures in the stand exceed atmospheric, and should not be absolutely airtight. As an added precaution against failure, do not lay pipe in extremely hot, ex- , tremely cold, or in wet weather. If pipe should push into structures, this is generally not serious, since it can be remortared to the stand. Procedure is specified so that the pipe can move into the stand and not crush it. Use of fertilizers. An important cause of concrete deterioration is the addition of ammonium sulfate fertilizer to the water before it goes through the pipe. Ammonium sulfate is not recommended as a fertilizer to be applied in irrigation water except for occasional use, and never at concentrations above 0.1 per cent. The lines should be flushed immediately after its use. Ammonium nitrate can cause some deterioration, but is safe if concen- trations never exceed 1 per cent, and if the lines are flushed after application. No other commerical fertilizers have been found to cause deterioration of concrete. Use of soil amendments. Generally speaking, there have been no direct ex- periments on the effect of various soil amendments on concrete. But as many contain sulfates, which are generally harmful to concrete, it is safest not to add soil amendments to irrigation water be- fore it goes through concrete pipe sys- tems. There is one known case in which a patented soil amendment, added to the water, caused a release of sulfuric acid vapor along the crown of a pipe line, re- sulting in deterioration of the crown. Gypsum is the most common soil amend- ment used, and is sometimes added to water before it goes into pipe lines. Be- cause gypsum has a very low solubility, its adverse effect upon concrete would be slow. The practice of adding gypsum to irrigation water is only a few years old, which may explain why damage has not yet been observed. But the farmer should be aware that, by adding gypsum to water going into concrete pipe lines, he risks injuring the pipe— to what extent is not, at present, known. Making repairs. Longitudinal com- pression helps prevent circumferential cracks resulting from temperature drop. If, in making repairs, one or more sec- tions of pipe must be removed, this longitudinal compression can be lost be- cause the two ends of pipe will move together slightly. This can be partially prevented if the line is allowed to dry out as much as possible for several days to a week before repairs are made. To facili- tate drying out, remove all water from the line, and open all possible hydrants, gates, and stands to facilitate air circulation. Also, be sure that the sections of pipe used in making repairs are thoroughly dry when they are installed. Backfill with moist soil around the pipe. Surges in pipe lines. As indicated, surging is one of the common disadvan- tages of open type systems with overflow stands. Air becomes entrained in the water as it overpours the lip into the downstream portion of the overflow stand. This intimate mixture of air and water is carried down into the reach of pipe down- stream from the stand, and, because of the turbulence of the flow, the tendency for the air to separate out is minimized. Therefore, after a short interval, the up- stream portion of this reach of water be- comes lighter than the downstream por- tion — sometimes causing a reversal of hydraulic gradient until the water with [43] entrained air flows back to the stand and the air is dissipated. Thus, forward flow is only in cycles. The pipe line functions at only a fraction of its capacity, and the water is difficult to handle. The following observations have been made with regard to surging: 1. Most trouble occurs at low flows be- cause at near capacity flows there is little, if any, fall of water over the baffles. It may not, however, be possible to open up to full flow because of the surge. 2. When the reach of pipe immediately downstream from the overflow stand causing the entrainment has sufficient grade, the air appears to accumulate gradually along the crown of the pipe and to blow back upstream to the stand. Also, the pipes are often flowing only part full. Thus, in this case, surges do not develop. As yet it cannot be stated whether or not there is a minimum grade above which all air will blow back and prevent trouble. 3. Relief is obtained by placing gate valves in the baffle walls (or between the upstream and downstream portions) of overflow stands, and closing these gates only enough to create the pressure neces- sary for operation of upstream hydrants or laterals. This changes the hydraulic characteristics of the system. With a straight overflow stand system, each stand keeps upstream heads quite constant so that there is no appreciable upstream change in deliveries (into laterals or out of hydrants). Any water that spills over the baffle is surplus from the upstream deliveries. Thus, the far end of a system may have a surplus or a deficiency of water if flow into the system is not exactly correct. Where there are gate valves in the overflow stand baffles, the water levels in the stands will vary with the flow. Thus, upstream deliveries and flow through the baffle gate valves will vary somewhat, and any "errors" in flow into the system will tend to be proportioned throughout. This eases the problem of regulation, but de- liveries may not be constant. Whether this is an advantage or a disadvantage de- pends upon individual circumstances. 4. Relief is obtained by placing an airtight cover over the overflow stand in question. This method tends to create a vacuum in the stand, thus inhibiting the entrainment of air. This vacuum aifects the hydraulic gradient to the extent that discharge into hydrants and laterals up- stream is uncertain, and the capacity of the pipe line downstream is decreased. The airtight cover may act like a flap valve — seal when there is a vacuum in the stand, but lift for relief if positive pressure should be created. This type system is largely experimental, with breather pipes from the lids extending into the water upstream from the baffles to provide more constant upstream deliv- eries. It is not recommened as yet. 5. Use of an overflow stand, with a re- latively large cross-sectional area of the downpour section, may minimize the trouble. The downward velocity is low, and much of the air may be released be- fore the water gets into the pipe line. 6. Sometimes surge gradually builds up in flowing downstream from reach to reach of pipe. Surge can be dampened by certain irregular spacing of overflow stands. The idea is not, however, generally applicable to farm systems. Some Systems Are Now Using MONOLITHIC PIPE Monolithic or "mole" pipe systems are becoming more common on farms served by irrigation districts which deliver water at higher rates than can be well handled by the prefabricated pipe. The plain con- crete irrigation pipe, prefabricated, is limited to a maximum size of 20 or 24 inches, depending upon locality and in- staller. The monolithic pipe ranges in size from 24-inch to 42-inch. Hand methods of fabricating mono- lithic pipe were initiated about 1930. 44] The invert or lower half of the pipe is first formed by drawing a sled with a semi- circular bottom through poured wet con- crete in the bottom of a trench that has been carefully excavated so that its sides and bottom serve as a form. The arch or upper half of the pipe is later formed by hand-troweling poured concrete over a collapsible, semicircular steel form. The pipe may not be truly round, and may not be as perfect as prefabricated pipe, but it has a number of advantages over the lined canal — the structure with which it is competitive. The machine-made monolithic pipe eliminates the need for construction joints along each side and reduces the labor requirement for placing. The ma- chine, with a maximum laying rate of 100 feet per hour, is on a sled which is pulled along the trench bottom by a cable winch. Wet concrete is poured into a hopper on top and is vibrated into the spaces between the trench bottom and sides and the slip forms of the sled. Temporary, collapsible forms are left under the arch until the concrete is set. As with the handmade monolithic pipe, openings in the top of the pipe for vents and hydrant risers are made as the pipe is formed. Lack of good comparisions, and lack of thorough tests of strength and dur- ability, make it impossible to compare monolithic pipe systems with the pre- fabricated ones. Actually, except for the 24-inch size, the two types are in no way competitive. Prefabricated concrete pipe would usually be reinforced in similar sizes, and might cost about twice as much as the monolithic pipe. Hydrants and stands are constructed similarly for both types of systems, and are installed in the same manner. [45 CONTRACT AND SPECIFICATIONS FOR THE INSTALLATION OF A CONCRETE PIPE IRRIGATION DISTRIBUTION SYSTEM The contract: Date:. The seller The buyer:. name of seller address of seller name of buyer address of buyer Location of proposed work:. The seller, subject to acceptance within 30 days of the above date, agrees to fur- nish material for, and install a concrete pipe irrigation distribution system, or portions thereof, in accordance with the plans and profiles (if any) prepared by (buyer or seller), and in accordance with the standards and specifications of circular 418, "Concrete Pipe for Irrigation," of the University of California, College of Agriculture, Berkeley 4, California (1952, or latest revision thereof), at the above location. The system shall consist approximately of the following lengths of pipe line: Size Length iide diameter (approx.) Cost per Approx. total inches feet foot cost Bands shall not be required. (Cross out "not" if bands required.) The system shall also consist of the following structures: Quantity Code Size Unit no. letter 1 (inches diam.) Description 2 cost Total cost Approximate total cost, pipe line and structures $ 1 Code letter as given in Circular 418. 2 For certain hydrants, give the number of outlets in each, and sizes of outlets in inches inside diameter, and give make and specifications for any appliances, such as orchard valves, alfalfa valves, slide gates, etc. For stands and line structures, give the number, size, make, and quality of all appliances, such as gate valves, in each. On hydrants with pots, show size of pot and size of riser. [46] ^ (buyer or seller) agrees to haul above articles from seller's yard, to distribute these properly along trench side at location specified, and to return any remainder to seller's yard in good condition, all at his own risk I and expense (buyer or seller) agrees to dig and complete backfill of any and all trenches required. Backfill to a depth of at least 6 inches above the top of the pipe shall in all cases be placed by the seller. If soil other than that excavated is required for the initial backfill, same will be supplied by the (buyer or seller) and delivered by him to trench side at convenient intervals. The soil for initial backfill must be moist. If it is dry, the furnishing of water, without cost, to moisten it shall be a responsibility of the buyer, and the actual wetting shall be done by the (buyer or seller). If the soil along the pipe lines must be moistened before trenching, such irrigation as is necessary to wet to the depth of trenching is a responsibility of the (buyer or seller), and the water shall be furnished at the site free of cost by the buyer. The buyer shall furnish all water for testing the system, free of cost. \ The seller guarantees the system for one year against faulty materials and work- manship, and any repairs from these causes shall be at his expense. The guarantee does not apply to earthquakes, land settlement (except from improper trench bottom preparation) , or external damage not caused by the seller's men or equipment. Payment will be on the basis of unit prices listed above and of quantities as determined after installation, but as substantially agreed to herein or as a subsequent modification of this contract. The contract shall be completed within days of acceptance, and if not so completed, the cost to the buyer of failure to complete is estimated at dollars per day, and such amount shall be deducted from that owed the seller. The seller shall not be held responsible for delays caused by acts of God, strikes, or other causes beyond his control. Terms shall be in cash in full upon satisfactory completion and testing, or they shall be one third of the total amount of the contract upon signing, one third upon completion of delivery of the pipe to the job, and the balance upon satisfactory completion and testing of the system (cross out one), and shall include interest on any unpaid balance at the rate of per cent, compounded annually, from the date the system has been satisfactorily completed and tested. In event any legal action is necessary to enforce this contract or portions thereof, the party against whom judgment is rendered agrees to pay reasonable attorney fees and costs to the other party. Buyer Seller Signed by Signed by i Date accepted [47] The specifications: 1. Pipe. The pipe shall conform to the standard specifications for concrete irri- gation pipe (A.S.T.M. designation: C 118-39, or a revision thereof) of the American Society for Testing Materials, with the following modifications: a. The specifications for Portland cement shall be changed to A.S.T.M. designations nos. C 150-49 or 175-48T, Type I or II. If other than Type I cement is to be used, it will be so specified by the purchaser. b. The sentence reading "The maximum size of coarse aggregate used shall not exceed one third the shell thickness of the pipe" is eliminated. c. The drying temperature for absorption test specimens shall be 110° C ± 5° C, and specimens shall be weighed for dry weight while still warm. d. Curing of pipe shall consist of keeping the pipe continuously and uniformly wet for a period of 7 days after fabrication. 2. Pipe shall be at least 21 days old, and shall be dry, when it is laid. 3. Laying mortar. Cement for laying mortar shall be Portland cement A.S.T.M. designation C 150-49 Type I or II. Approved plastic or approved waterproof cements may be used, but no lime or plasticizer shall be added to these. The mortar shall be composed of not less than one part cement to two parts of clean, well-graded sand which will pass a 1/8-inch mesh screen. When plastic or waterproof cement is not used, an admixture may be used not exceeding one of the following percentages by volume of cement: hydrated lime, 5; fire clay, diatomaceous earth, or other suit- able inert material, 20. Consistency of the laying mortar shall be such as to adhere to the ends of the pipe while being laid and be squeezed out of the joint easily when the pipe sections are placed together. 4. Grade and alignment. Pipe lines shall be straight and of uniform grade between stands or anchors, except as provided in paragraph 12. Trenches shall be dug true to line and grade, as checked immediately before the pipe is laid, with straight sides and with bottom smooth and free from all hard material and high or low spots. 5. Dimensions. All trenches shall be of sufficient depth to provide a minimum cover over the pipe of 24 inches in loams and coarser textured soils, and a minimum cover of 30 inches in clay loam and clay soils. This requirement shall be governed by the usual texture of the soil horizon at the pipe depth rather than by the texture of the sur- face soil. Also, in clay soils which show evidence of swelling or cracking, the trench shall be excavated 2 inches below grade and shall be brought up to grade with a com- pacted layer of loam or coarser textured soil or sand. For width, the trench shall have a minimum clearance on each side, between the outside of the pipe and the sides of the trench, of 6 inches for pipe up to and including 18 inches, and of 8 inches for 20- to 24-inch pipe. 6. Trench bottom. If the trench bottom is soft or unstable, the loose or unstable soil shall be removed and the trench then backfilled and thoroughly compacted to grade with gravel or sand, or suitable soil of loam of coarser texture, to the end that the pipe shall have a firm support. If the trench is excavated in rock, boulders, or other hard material, it shall be excavated at least 4 inches below grade and refilled with sand or similar selected granular material, and thoroughly compacted to grade, leaving approximately % inch bedding of loose loam or sand for the pipe. Any free water encountered in the trench shall be removed before the pipe is laid. 7. Laying and jointing. The first section of pipe shall be placed in the center of the trench with the tongue end pointing in the direction to be followed by the pipe laying. [48] Space shall be scraped out, with the pipe layer's trowel, under and immediately in front of the end of each section laid. This space shall be filled with laying mortar, prior to placing the next section of pipe, in a mound sufficient so that, if banded, the band will be continuous around the pipe. The ends of the pipe shall be cleaned and wetted before applying mortar. The groove is to be filled with mortar; care shall be taken that no mortar falls from the joint before ends are- abutted; and the groove end is to be pushed onto the tongue end of the other section so that they abut snugly, with well aligned inside surfaces, and so that mortar is squeezed out on both the inside and outside of the joint. The interior surface of the joint shall be brushed smooth, and surplus mortar removed. Normally the pipe is not shifted after the joint is completed, but, if slight adjustment is necessary, both the inside and the outside of the joint shall be carefully brushed again, and as the joint is completed, enough earth shall be placed at the side, near the center, of the last section of pipe to prevent further move- ment. Every reasonable effort shall be made to complete the laying of pipe between structures as quickly as possible. 8. Banding. When external bands are specified, they shall be placed over the joints never less than two nor more than five sections behind the laying. The mix for banding mortar shall be the same as specified for "laying mortar" in paragraph 3 above. It shall be plastic and of such consistency that the band will adhere to the side of the pipe. The external surface of the pipe shall be cleaned and wetted to insure proper bond with the band. There shall be continuous union between the joint mortar and the band mortar. The band shall be not less than % inch thick at the joint and shall be feathered out on each pipe section approximately 2 inches. The edges of the band shall adhere to the pipe surface, and shall be finished in a workmanlike manner. 9. Initial backfill and protection. An initial backfill of sand or similar selected granular material shall be placed to a height of 6 inches above the top of the pipe for the full width of the trench, not more than seven sections of pipe behind the laying. If the soil is not moist, and if the relative humidity of the soil is low, the soil shall be wetted before or immediately after placing. Under no circumstances shall water be permitted to flood the trench at this time. No clay soil that shows evidence of excessive swelling or cracking shall be used for this initial backfill. Care must be exercised to avoid injury to the bands. All openings in the pipe lines and structures shall be plugged, such as with sacks and earth, except where and while work is actually in progress, and shall be kept plugged until the pipe line is completed and it is to be filled with water. 10. Initial filling. Although he may not avoid responsibility for any rips, the seller may elect, in lieu of or in addition to wetting the initial backfill, to fill with water each reach of pipe line not later than 72 hours after laying any portion of that reach, and not sooner than 24 hours after completion of that reach. The reach of pipe line shall remain filled for at least one hour, and the maximum head at this time should not exceed 2 feet. 11. Structures. All structures shall be vertically true, and in accordance with the designs and standards specified in this circular, where applicable, or in accordance with separate specifications included in the contract. The following details shall be adhered to, where applicable: a. Connections to pipe lines. Openings cut into stands for connections to pipe lines shall be slightly greater than the outside diameter of the connecting pipe. Such open- ings shall be cut either before the structure is placed or after joint mortar has cured sufficiently to prevent damage. All connections shall be strongly cemented together with the laying mortar heretofore specified and shall be clean and wet before the [49] mortar is applied. All exterior joints of vertical structures wherein irrigation pipe is used shall be banded in accordance with the procedure as herein outlined for pipe lines. Both the inside and the outside mortar faces shall be brushed smooth, where possible. No pipe spalls or other trash or obstructions shall be left in pipe lines or structures. The same specifications shall apply to the connecting of hydrants or stands on the top of an installed pipe line, except that the opening cut into the pipe line shall be within 1 inch of, but not greater than, the inside diameter of the riser or stand. b. Pipe for structures. Unless otherwise specified, all hydrant risers and all stands 24 inches or less in diameter shall be constructed of plain concrete irrigation pipe as heretofore specified, or of sewer (bell and spigot) pipe of equal quality. All stands of diameter greater than 24 inches shall be constructed of reinforced concrete pipe as specified by the American Society for Testing Materials (A.S.T.M. designation C 75-41, or the latest revision thereof) . Those specifications shall be modified by the provisions la and lc above. c. When placed. All stands of diameter greater than the pipe line shall be installed before the pipe line is laid, and the pipe lines shall be connected to and mortared into such stands immediately as they are being laid. Hydrant risers, and stands equal in diameter to the pipe line, or smaller in diameter, and of the types shown in the draw- ings of this circular as being installed over a pipe line, are to be installed after the pipe line has been placed. d. Bases of stands. The first section of pipe for stands shall be placed on the base concrete before initial set of that concrete, or the pipe shall be placed first and the concrete poured and tamped in and around the pipe. Concrete for bases of stands and for anchors shall have a 28-day compressive strength of 3,000 pounds per square inch. Concrete bases of stands shall have a diameter at least 10 inches greater than the out- side diameter of the stand ; shall be at least 4 inches thick for stands not over 18 inches inside diameter or over 10 feet high above the base; at least 6 inches thick for stands up to 30 inches inside diameter and not over 12 feet high above the base; and at least 8 inches thick for all other stands. After initial set and before final set of the concrete base, water to a depth of 4 to 6 inches shall be carefully poured into the stand, or it shall be loosely covered with about 6 inches of moist soil. e. Height of stands. Height of all stands shall be such as to provide at least 2 feet freeboard above the maximum hydraulic gradient for the maximum flow specified. Tops of stands shall be at least 4 feet above the ground surface. f. Capped vent stands. These are vent stands of diameter smaller than the diameter of the pipe line. They shall be constructed of diameter equal to the diameter of the pipe for a distance above the crown of the pipe line equal to at least twice the diameter of the pipe, and at this elevation a cap, adequately reinforced against internal pressure and any external loads, is mortared onto the riser in such manner as to produce a watertight seal. The smaller vent pipe, of size and quality specified, shall extend through this cap and up to such height as to provide a minimum of 2 feet freeboard with the maximum design hydraulic gradient, and to a minimum height of 6 feet above ground surface, except where topped by an air release valve. The vent pipe shall have a strong watertight connection to the cap, and shall be adequately guyed, if necessary, to provide stability. 12. Anchors at bends. A concrete anchor shall be cast over bends at any point where there is a change of grade or alignment of greater than 15 degrees, except at stands of diameter greater than the pipe line diameter. This anchor, in the form of a half ring around the bottom and sides of the pipe, shall have a minimum thickness of 6 inches on the sides; it shall be a minimum of 6 inches in length; and it shall fill a trench [50] extending at least 10 inches below pipe bottom cut into undisturbed soil. The pipe shall be clean and wet, to the end that a good bond is obtained between anchor and pipe. 13. Testing. The pipe system shall be tested under full pressure, but no sooner than three days nor later than 10 days after installation has been completed. The test shall run for 8 hours, and any leaks existing just before completion of the test shall be care- fully repaired, and the system shall again be tested until free of leaks. In making this test, a leak is considered to be water coming to the surface level above the pipe line after the trench has been completely backfilled. In order that the information in our publications may be more intelligible, it is sometimes necessary to use trade names of products or equipment rather than complicated descriptive or chemical identifications. In so doing, it is unavoidable in some cases that similar products which are on the market under other trade names may not be cited. No endorsement of named products is intended nor is criticism implied of similar products which are not mentioned. Co-operative Extension work in Agriculture and Home Economics, College of Agriculture, University of California, and United Ktates Department of Agriculture co-operating. Distributed in furtherance of the Acts of Congress of May 8, and June 30, 1914. J. Earl Coke. Director, California Agricultural Extension Service. 20m-ll,'52(A1394)L.L.