Agriculture Reference
In-Depth Information
Throt tling valve s
simpl y restrict pump outpu t, depen ding on how
much the valve is open. These valves are used with centrifugal pumps, whose
output is very sensitive to the amount of restriction in the output line.
Spring-loaded bypass valves
(with or without a diaphragm) open or
close in response to changes in pressure, diverting more or less liquid back to
the tank to keep pressure constant. These valves are used with roller, dia-
phragm, gear, and small piston pumps.
Unloader valves
work like a spring-loaded bypass valve when the
sprayer is operating. However, when the nozzles are shut down, they reduce
strain on the pump by moving the overflow back into the tank at low pres-
sure. These valves should be used on larger positive-displacement pumps
(piston and diaphragm) to avoid damage to the pump or other system compo-
nents when the nozzles are cut off.
7.
Agitators
Every sprayer must have agitation to keep the spray material uniformly
mixed. If there is too little agitation, the pesticide will be applied unevenly.
If there is too much agitation, some pesticides may foam and interfere with
pump and nozzle operation. The type of agitation necessary depends on the
pesticide formulation to be used.
a.
Bypass Agitators
Soluble powders and liquid formulations such as solutions and emulsifi-
able concentrates require little agitation. Bypass agitation is sufficient for
these formulations. Bypass agitation uses the returning liquid from the pres-
sure relief valve to agitate the tank. The return must extend to the bottom of
the tank to prevent excessive foaming.
Bypass agitation is not sufficient for wettable powders or in tanks larger
than 55 gallons unless a centrifugal pump is used. Centrifugal pumps usually
have outputs large enough to make bypass agitation adequate even for wettable
powders in tanks less than 100 gallons.
b.
Hydraulic (Jet Action) Agitators
Hydraulic agitation is required for wettable powder and flowable formula-
tions in small tanks and for liquid formulations in 100-gallon or larger tanks
with gear, roller, piston, or diaphragm pumps. Hydraulic agitation is provided
by the high-pressure flow of surplus spray material from the pump. The jet
