144 



BuivLE^TlN 86 



design for a square gate pit is shown in Fig. 28. The walls are of 

 1:2:4 concrete 4 inches thick. The base is extended to prevent 

 undercutting in case the flow overtops the pit. The largest size 



of gate that can be set in so small 

 a pit is 18 inches in diameter. If 

 the pit is at the head of a lateral, 

 two gates are set, one on each out- 

 flow. No gate is put on the inflow 

 pipe because the pit serves as an 

 outlet for air. The most frequent 

 type of gate pit is made of regular 

 lengths of cement pipe. Usually 

 small sizes are employed and it 

 is not possible to descend into the 

 pit to repair or replace the gate, 

 as would be feasible in a pit 30 

 inches in diameter. In general, 

 gate pits, like tanks and reser- 

 voirs, should be circular in sec- 

 tion. 



Several good designs of gates 

 are on the market. One has a 

 beveled seat and is brought to 

 place by means of a square- 

 threaded nut engaging a long 

 rack. There can be no water 

 hammer caused by a gate of this 

 type. Another design has a lock- 

 nut and, when it is loosened, the 

 gate can be lifted or dropped 

 to another position and there 

 clamped. The plain slide gates 

 are not to be recommended; they depend upon the water pressure 

 to make them tight, and they usually leak. 



Fig. 29. — Riser and circular valve for 

 taking out water for orchards 

 or row crops. 



RISERS 



The ordinary risers used in orchards are as shown in Fig. 29. A 

 riser is placed at the head of each row of trees and the four small 

 streams of water taken through the small openings are run down 

 four furrows, two on each side of the trees. From 5 to 30 gallons 

 a minute are run in each stream, depending on the character of the 

 soil, the slope of the land, and the length of run 



