UNIVERSITY OF CALIFORNIA • COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY 4, CALIFORNIA THE PORTABLE IRRIGATION SIPHON AND A NEW PRIMING VALVE FOR SIPHONS C. N. JOHNSTON 1 The war-induced shortages of labor and materi- als have stimulated the search for simpler methods of irrigating to eliminate labor, and for substitute materials and equipment to re- place items no longer available. Thousands of 2-inch siphons (fig. l) made of metal, plywood, or plastic have been used in recent years, Siphon Figure 2 gives test data resulting from in- vestigation of several 2-inch siphons having smoothly finished inside joints at the bends. Any 2-inch siphon of like construction should give similar performance. Siphons with rough inside joints will perform less well than smooth ones and will give less flow for any given head Wale Fig. %W' 1. --Two-inch siphon made of metal, plywood, or plastic, mainly to irrigate row crops such as tomatoes, beets, and beans. The chief advantage of siphons is to permit the water to pass from the ditch over the ditch bank into the field without cut- ting into the bank. One man, handling a maximum of 150 siphons, can easily irrigate an area that would otherwise require two or more men for shoveling banks and attending to ditches. The handling of large-size siphons is laborious part- ly because of difficulties in their priming. To overcome this, a priming valve has been designed to be used with 2-inch or larger siphons. Portable Two-Inch Siphon The first problem of the new user of these siphons is to decide how many he needs. The discharge of each one becomes greater along with the net head in inches; that is, the flow in- creases when the distance from the water surface in the field up to the water level in the ditch has increased. This difference in the two water- surface elevations is the head. For any given installation, there is a limit to the amount of head; the greater the head, the more likely the ditch is to leak through the banks and wash out. Claylike banks are safer for high heads than sandy banks. Assistant Professor of Irrigation and Associ- ate Irrigation Engineer in the Experiment Station. (perhaps as much as 10 per cent less flow). Table 1 furnishes the same data as figure 2, but only for selected heads and corresponding flows. The graph is actually the complete picture of the performance of the 2-inch siphon. The irrigator not only must decide how many siphons are necessary, but he also must know how much head is safe and how much water the group of siphons should deliver from the ditch to keep up with the supply. For example, if 1.5 cubic feet per second (c.f.s.), or roughly 675 gallons per minute (g.p.m.), are supplied by a pump, and a head of 3 1/2 inches is safe from ditch-water level to field-water level, he must know how many siphons are needed to use this supply. Figure 2 shows inches of head on the vertical or side line, and gallons per minute on the horizontal or bottom line. Since the safe head is 3 1/2 inches, one may. start at this point on the chart and move horizontally to the slope line. At this point direction is changed; going straight down a vertical line, the bottom line is joined at 27.8 g.p.m. For computation, using a lower value, such as 27.5, would provide a margin of safety. Then, the problem of how many siphons handling 27.5 g.p.m. would be required to provide 1.5 c.f.s., or 675 g.p.m. is solved as follows: = 24.5 or 25 siphons. LI] 27.5 the result will be the same UNIVERSITY OF CALIFORNIA LIBRARY COLLEGE OF AGRICULTURE DAVIS If table 1 is used. 10 e 7* 3.5V/7c/> head "7 / 1 • r i ii 0*| s> 1 l-» * oa i 10 IS 20 30 4 50 «0 70 80 90 100 6affons per minute. Fig. 2. --Test data from several similar 2-inch siphons showing average performance. TABLE 1 Heads and Capacities for Two-Inch Siphons Head(h) Discharge Head(h) Discharge in in in in inches g.p.m. inches g.p.m. 0.8 13.0 5.5 35.0 I . J 14.5 6.0 36.8 1.5 17.9 6.5 38.1 2.0 20.8 7.0 39.8 2.5 23.4 7.5 41.1 3.0 25.6 8.0 42.7 3.5 27.8 8.5 44.0 4.0 29.7 9.0 45.2 4.5 31.7 9.5 46.5 5.0 33.3 10.0 47.9 Although the minimum number of siphons is 25, a few more will be needed. The operator will not wish to shut down his pump; so, if he has 6 to 12 additional siphons, he can use them when he is ready to move to another field. He will start the extra ones in the new location, pick up some of those finished at the first field, put them in operation at the new field, return for the rest at the old field, and continue this process. He will start each siphon by dipping one end into the ditch while holding his hand over the other end — the highest point on the siphon, although it is now being held as low as possible. He will make two or three longitudinal thrusts with the siphon, forcing the submerged end quickly through the water with each thrust. Since his hand over the unsubmerged end acts as a valve, the displaced air caused by the thrust escapes under pressure but is not allowed to re- turn. When the water reaches his hand at the upper end of the siphon, the siphon is lowered to the field, and then his hand is removed. Flow begins at once. Siphons 3 and 4 inches in diameter are light enough in weight to be managed by hand, but difficult for one man to prime unassisted. They give discharge rates greater than the 2-inch size. The capacities of 2-, 3-, and 4-inch siphons may be roughly compared as follows: Relative capacity 2-inch siphon 1 3-inch siphon 2 1/4 4-inch siphon 4 One can infer that the 3-inch siphon will de- liver about 2 1/4 times as much as the 2-inch for the same head, whereas the 4-inch will de- liver about four times as much as the 2-inch at a constant head. Priming Valve for Siphons One can prime 2-inch siphons by using the hand as a valve over the upper end of the siphon tube. Since, however, the hand cannot readily close larger units at the end, other expedients must be introduced. A common practice has been to slip a tight-fitting canvas sleeve, a foot or so long, over the field end of such siphons for 2 or 3 inches. Then, after the whole siphon is submerged in the ditch, the loose or open end of the canvas sleeve is folded or rolled up, or is bound with twine or wire to form a seal. Then the field end of the siphon is lifted from the ditch into the field, and, when the seal is re- leased, the flow starts. A man can accomplish this process with siphons up to about 4 inches in diameter. With a larger diameter, however, more energy is demanded; a car, truck, or tractor often can supply the needed power to move the sealed end over to the field side of the ditch bank. To expedite the priming of 3- and 4-inch si- phons, and to facilitate the use of larger sizes, the priming valve mentioned in the introduction has been developed to replace the canvas sleeves and hasten the priming process. This valve (fig. 3) accomplishes the same purpose as does the hand with the 2-inch siphons. It consists of a tapered plug (b) which fits the inside of the siphon (a) and forms a seal; a spring-loaded flat disk valve (d) seats on the outer face of the plug. The plug itself is wrapped with sheet rubber (c) or similar seating material. The shroud (h) protects the valve and valve stem, and diverts the water away from the operator when the siphon becomes full during the surging action involved in priming. Without the shroud, the water ejected from under the valve disk would spray the operator. The valve shown in figure 3 is of masonite , with a rubber facing made from an old inner tube. The* valve seat on the plug was machined smooth. The materials and design details used in the priming-valve assembly shown in figure 3 are suggestions only. A light-weight metal disk could be substituted for the masonite disk of the valve, and rubber facing might not be needed to improve the seal. The disk (d) could seat on b if e. were located outside of b. The shroud then would be soldered to e. Or e might even be eliminated if the shroud (h) could be shaped beyond where h joins b so there would be about l/4-inch clearance between the valve disk and h. Twine or wire may be used to fasten sheet rub- ber or similar sheet material to the tapered face of the plug. The rubber facing for the valve disk can be cemented on with cellulose cement . Dimensions are not critical for any part of the priming valve so long as there is a suffici- ent opening for the release of air. The spring load (f) is light (only a few ounces). The valve disk may work on a hinge instead of being center-guided and loaded. After the assembly is placed at the end of a siphon, priming is accomplished at the surging action previously described for the 2-inch units. If the valve seats tightly on the plug seat, two or three good surges are sufficient to prime a siphon of [3] manageable length. The use of such valves might make the priming of 3- or 4-inch siphons as rapid in the field as the hand-priming rate for the 2-inch type. Only one priming valve needs to be made for use with a large number of siphons of a given size because the valve unit is removed after each priming, and is carried along by the operator to the next siphon. CL Fig. 3 • --Priming valve for siphons. The dimen- sions of the parts are dependent on the size of siphon to be fitted. [4] 4m-Nov. , ' 45 (6178)