Centrifugal Pumps Centrifugal pumps, figure 4, are most popular for low-pressure sprayers. An impeller with curved vanes rotates at high speed inside a disk-shaped casing. Liquid drawn in at its center is thrown by centrifugal force into a channel around the edge. The high-velocity spray liquid is forced out the outlet, generating pressure in the outlet line. The design of the pump, especially the diameter and speed of the rotating impeller, affects the efficiency in developing outlet pressure.
Some pumps have a planetary gear system that is enclosed and mounted directly on the PTO shaft.
The pump may also be driven by a direct-connected hydraulic motor that operates off the hydraulic system. The advantage of such an arrangement is that the motor maintains a more uniform speed and output, and frees the tractor PTO for other purposes. Centrifugal pumps can develop pressures up to 75 psi but output volume drops off rapidly when outlet pressure exceeds 30 psi. This decrease in volume, however, can be and advantage because it permits controlling nozzle pressure without a relief valve. Typical maximum working pressure is 50 to 60 psi.