Flow Control: Controlling Pump Slip in Positive Displacement Pumps -

Flow Control: Controlling Pump Slip in Positive Displacement Pumps

  • Schematic showing back pressure regulator used to stabilize flow rate with positive displacement pump

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.

Background

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.

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schematic showing the Equilibar back pressure regulator with a metering pump</p><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /><br /> <p> and positive displacement pump in a liquid product blending application

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:

Equilibar offers both industrial back pressure regulators and sanitary back pressure regulators to meet a wide range of chemical blending applications.

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GS Series Back Pressure Regulator made from PVDF Kynar

GS Series Back Pressure Regulator made from chemically resistant PVDF

 

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