The constant volume control responds to a pressure drop across an orifice and can be used effectively in two different control modes.

In one system let's assume the requirement is to provide a constant flow of 10.5 gpm regardless of pump input speed within the limits of the pump. This system will use a fixed orifice sized at 10.5 gpm at 150 psi pressure drop. The PV 325 pump will deliver 8 gpm at 600 rpm; the PV 425 pump will deliver 10.5 gpm at 600 rpm. As the pump speed increases, flow will increase resulting in Increased pressure drop across the fixed orifice. This signal is fed back to the sensor which adjusts the reaction plate angle to re-establish the 150 psi pressure drop across the orifice, thus maintaining a fixed flow of 10.5 gpm from the pump. At maximum pump speed the reaction plate will be a relatively small angle to deliver this fixed flow. As pump speeds decrease, the pressure drop across the orifice falls resulting in the pump control repositioning the reaction plate at a larger displacement to maintain constant flow into the circuit.

Note: As speed decreases torque increases if discharge flow and pressure remain constant.

The other system involves a remote variable flow requirement with a fixed input speed to the pump. This system operates on the same principles as outlined above except a variable orifice is used. As the orifice is varied the reaction plate will assume an angle to satisfy the 150 psi pressure drop requirement across the orifice.

With a given orifice, and from no load to full load, the pump will provide a constant flow within ± 10%. A relief valve is required in all systems.

OPTIONAL ADJUSTABLE VOLUME — The maximum desired volume to be pumped can be controlled by the volume limit adjustment. This adjustment screw limits the maximum angle of the reaction plate to a predetermined maximum.