All you need to know about Liquid Ring Vacuum Pumps

Liquid Ring Vacuum Pumps or LRVPs are essential for a wide range of industries ranging from Power generation to pharmaceutical and food production.

What is a Liquid Ring Vacuum Pump?

A liquid ring vacuum pump (LVRP) is a rotating positive-displacement pump. LVRPs are typically used as vacuum pumps, but can also be used as gas compressors. The function of a LVRP is similar to a rotary vane pump, with the difference being that the vanes are an integral part of the rotor and churn a rotating ring of liquid to form the compression-chamber seal. They are an inherently low-friction design, with the rotor being the only moving part. Sliding friction is limited to the shaft seals. LVRPs are typically powered by an induction motor.

“The earliest liquid-ring pumps date back to 1903 when a patent was granted in Germany to Siemens-Schuckert.”

Principle of operation

The liquid ring pump compresses gas by rotating a vaned impeller located eccentrically within a cylindrical casing. Liquid (usually water) is fed into the pump and, by centrifugal acceleration, forms a moving cylindrical ring against the inside of the casing. This liquid ring creates a series of seals in the space between the impeller vanes, which form compression chambers. The eccentricity between the impeller’s axis of rotation and the casing geometric axis results in a cyclic variation of the volume enclosed by the vanes and the ring. Gas, often air, is drawn into the pump through an inlet port in the end of the casing. The gas is trapped in the compression chambers formed by the impeller vanes and the liquid ring. The reduction in volume caused by the impeller rotation compresses the gas, which reports to the discharge port in the end of the casing.

Liquid Ring Vacuum Pumps
LVRPs are typically used as vacuum pumps, but can also be used as gas compressors.


The earliest liquid-ring pumps date back to 1903 when a patent was granted in Germany to Siemens-Schuckert. US Patent 1 091 529 for liquid ring vacuum pumps and compressors, was granted to Lewis H. Nash in 1914. They were manufactured by the Nash Engineering Company in Norwalk, CT. Around the same time, in Austria, Patent 69274 was granted to Siemens-Schuckertwerke for a similar liquid ring vacuum pump.

Pump sizes

LRVPs are available with a capacity as low as 4m3/hr and can go up to around 33 000m3/hr with vacuum ranges from atmospheric pressure down to vacuum levels of 33 mbar abs provided the service liquid temperature is optimal. Motor kW ratings from 0.075kW up to 600kW are used to drive these units.


Cast iron is the most common material used for the bodies and end plates of the pumps with impeller options in ductile iron, bronze, 304 or 316 stainless steel. Certain manufactures manufacture LRVPs from speciality metals such as Hastelloy, a nickel alloy that is particularly resistant to corrosion.

Industries that use LRVPs include

  • Power generation
  • Petrochemical
  • Seawater de-aeration
  • Pharmaceutical
  • Ground water remediation/vapour extraction
  • Food production


For more information or assistance in selection and a no-obligation quote or if you need a unit repaired or replaced kindly contact Air & Vacuum Technologies (Pty) Ltd.

We stock a variety of sizes with and without motors.

0861 VACTEC (822 832), [email protected]

Air & Vacuum Technologies

The leading provider of a wide range of equipment to all parts of South & Southern Africa, with our equipment being used in most industries.

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