USE OF CONCRETE PIPE IN IRRIGATION. 47 



to the hydrants (fig. 29). This portable pipe is made of light- 

 weight galvanized iron and is easily carried from one hydrant 

 to another. This method assures even distribution to each furrow, 

 and prevents washing at the stand. More labor during irrigation 

 is required, however. 



Where hillside land is to be irrigated, several new types of valves 

 have been developed (figs. 30 and 31). Most of these new valves or 

 methods of installation have been developed to assure an even flow 

 from valves in spite of considerable variation in pressure in the 

 orchard lateral. It is common practice in hillside irrigation systems 

 to install the main feed lines along the upper sides of the tracts and 

 to arrange orchard laterals to run down the steepest slope. As some 

 of these laterals run down for several thousand feet on grades that 

 fall from 15 to 35 feet per 100 feet, it can be seen that valves or outlets 

 must be arranged to continually relieve the pressure in the pipe. 



Fig. 29. — Distributing hydrant formed of portable pipe having small sliding gates. 



There are several distinct types of distributing systems designed 

 to control pressure. Overflow stands may be placed at stated inter- 

 vals down grade (fig. 26) , the stands being high enough to back water 

 up to the next relief stand above it, distributing hydrants being 

 placed between the relief stands. The relief stand may be made of 

 two parallel concrete pipes set vertically, as shown in figure 32, so 

 that water will rise in one to the required height, and overflow into 

 the other and thence down the pipe to the next stand. The common 

 orchard valve can be used to supply water to the furrows. The stand- 

 pipes may consist of one pipe of small diameter set in another as 

 described in a previous chapter. 



The second plan makes use of an ordinary open stand (fig. 33) 

 that does not stand above the ground surface over two or three feet. 

 A pressure gate is cemented to the intake pipe which can be closed 

 and back water up to the next box above. There is no danger of 

 excessive pressures if this plan is followed, providing that stands are 

 not placed too far apart or grades too steep, as water will back up to 

 next stand and overflow it if more water is let into the pipe line 

 than the orchard hydrants will dispose of. The disadvantage of this 



