USE OF CONCRETE PIPE IN IRRIGATION. 
49 
a pressure gate that controls the height of water in the stand. This 
arrangement is applicable where there is a constant down grade. 
Where excessive grades are encountered, it is usual to use overflow 
distributing hydrants. In this case each hydrant relieves the pres- 
Fig. 32. — Relief stand for preventing excess pressure on concrete pipe. 
sure at every tree row. It is not possible to pile up pressures that 
will exceed the height of the hydrants in this case, irrespective of the 
grade of the feed pipe. There are three general types of overflow 
hydrants used and each type may have several modification? 
Fig. 33. — Relief of pressure accomplished by short stands with pressure gates. 
The most common type consists of two lengths of concrete pipe 
(fig. 8) set vertically and adjacent to each other. The stand con- 
nected to the inlet pipe acts as the distributing hydrant and is fitted 
