Back Pressure Regulators With Positive Displacement Pumps
Back pressure regulators can be used downstream of positive displacement pumps to maintain a stable output flow rate, despite widely varying downstream pressure conditions.
Positive displacement pumps are often used to control the flow rate of liquid chemicals throughout industry. Examples of positive displacement pumps are:
- gear pumps
- lobe pumps
- progressive cavity
- piston pumps
- diaphragm pump
- peristaltic pumps
Of these, gear, lobe, and progressive cavity types can experience unwanted slippage with lower viscosity fluids, where a portion of the metered forward flow rate is lost due to back-flow. This slip for a given viscosity is generally proportional to the differential pressure across the pump.
In many blending and injection applications, the pressure downstream of the pump is not constant, but varies according to other process parameters, such as the flow rate of other blended components.
By installing a back pressure regulator downstream of the positive displacement pump, the differential across the pump is stabilizes, and therefore the degree of slip is controlled. In this way, the flow rate of the pumping system is stable and independent of system fluctuations downstream of the back pressure regulator.
The schematic at left shows how the flow rate of two chemicals are stabilized when injected into a larger header. In this case, the Equilibar back pressure regulator is controlled manually at a fixed rate using a common air pressure regulator to supply the 1:1 pilot set-point pressure.
As an alternative to this approach using variable frequency pump drives, there are also many ways to control flow rate:
- using our BPR as a pump pressure sustaining valve
- using our BPR as a flow control valve
- using our BPR for flow control from a pressurized supply