14 Farmers’ Bulletin 1185. 
requires carefully fitted valves and properly packed stuffing boxes. 
All commercial spray pumps are built in this way, but pumps which 
were intended for other purposes should be refitted when used for 
spraying. : 
The suction hose leading from the tank to the pump should be 
1 inch in diameter, with a heavy wall to prevent collapse. About 
10 feet of it is needed. 
Every engine-driven outfit must have a relief valve near the pump, 
permitting the surplus flow to return to the tank. This regulates 
the pressure and also acts as a safety valve to prevent the develop- 
ment of dangerously high pressures when the outlet is purposely 
or accidentally closed. 
The pump must have an air-pressure chamber large enough to 
keep the flow steady and thus insure even distribution of the poison. 
Its capacity in gallons for a double-acting or duplex pump should 
be about equal to the number of gallons per minute discharged by the 
pump, which is much more than the capacity of the chamber usually 
furnished with force pumps and even of many spray pumps which 
are intended to be used with a smaller number of nozzles. Triplex 
pumps need air chambers only two-thirds as large. The pressure 
chamber should be attached to the line near the pump, but not be- 
tween it and the relief valve, and it should be mounted in a vertical 
position to enable the settlings to drain out. It is best to provide the 
pipe leading to it with a check valve to retain the pressure in the 
chamber without strain upon the pump. 
A cut-off should be inserted between the pressure chamber and 
the strainer (described below), to prevent loss of pressure during 
short stops. A plumbers’ stop-and-waste cock is suitable for this 
purpose because it opens and closes with a single motion, The two 
ends are not alike, and it must be attached so that the closed end is 
toward the pump when the cock is turned off. 
THE PRESSURE GAUGE. 
A pressure gauge is necessary for good work with either a large 
or small outfit, because it is impossible without it to maintain the 
even pressure which is indispensable for the uniform spread of the 
poison. The gauge should be attached to the air-pressure chamber, 
or near it, and at a distance from the relief valve and the nozzles. 
THE STRAINER. 
Clogging of the nozzles by rust, scale, and fibers from the interior 
of the pump and the pipes can be prevented by inserting a strainer, 
so constructed that it can be cleaned easily, at some convenient place 
