Here are some of the devices that make a spraying system complete. Pressure regulators, figure 6, prevent possible pump damage by adjusting pressure within the operating limits of the pump. The pressure relief valve must be large enough to allow the entire pump output to return to the tank when the boom is shut off. Because the output of a centrifugal pump can be closed completely without pump damage, a pressure relief valve is not needed. If using a hydraulic agitator, agitation flow rate may be insufficient when the valve is unloading.
Control valves are all valves other than the pressure regulator that regulate the flow of liquid.
These control valves vary from a single valve that shuts off all the flow, to multiple valves for individual outlet controls, figure 8. Chemical flow in the boom can be directed to a portion of the boom, to the entire boom, or shut off completely by using a 3-section boom control valve, figure 9. With this valve it is possible to apply chemicals only from nozzles on the left, center, or right portion of the boom, or from any combination of these three sections. This is particularly useful when treating field edges and part of the boom is not required. Flow control valves are usually of two types.