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