Because the pump is literally the "heart of the system" careful consideration must be made in selecting the right pump. Seldom is there only one pump that will do the job. To make a wise choice, you'll need to know about pump types, how the pump is to be driven and the flow requirements for your specific spraying system and application.
To insure you can closely match the pump to your needs, Ag-Chem offers five types of sprayer pumps: roller, centrifugal, diaphragm, turbine, and piston pumps manufactured by Hypro, Ace Pump, Scot, ShurFlo and Delavan.
"Positive Displacement" vs. "Non-Positive Displacement"
Pumps can be divided into two general categories: "positive displacement" and "non-positive displacement". Roller, diaphragm, and piston pumps are positive displacement. That is, the flow from the pump is directly proportional to pump speed. This positive flow is why all positive displacement pump hook-ups must include a relief valve and bypass line between the pump outlet and the nozzle shut-off valve.
Centrifugal and turbine pumps are non-positive displacement. In these pumps, a rotating impeller creates a centrigual force that feeds the liquid through the system instead of capturing and discharging a fixed volume "per stroke" as rollers, pistons or diaphragms would do. Therefore, if the outlet is closed, the impeller simply continues to rotate harmlessly. That is why special relief valves are not required in centrifugal pump or turbine pump systems.