Liquid Ring Pump

The Versatility of Liquid Ring Vacuum Pumps – from contaminated fluids to priming action

Liquid ring vacuum pumps work on a similar principle to a rotary vane compressor or rotary vane pump. The liquid ring vacuum pump effectively stirs the liquid it is pumping into a vortex, creating a pressure seal without the complexity of diaphragms, valves or a reciprocating element.

Liquid ring pumps are simple to operate and therefore low in maintenance as the rotor is the only moving part. They are also efficient because their operation is based on rotary motion rather than reciprocation and their design is inherently low in friction.

Developed over 100 years ago, their design has been steadily refined and today they remain a popular choice for a wide range of applications in many different industries. Standard materials of construction include bronze or stainless steel for the impeller and cast iron or stainless steel for the housing. Other materials such as Hastelloy are also available for special applications.

Liquid ring vacuum pumps comprise of a main body forming a cylindrical pumping chamber, with its axis horizontal. Within this, a vaned impeller is eccentrically mounted (i.e. its axis of rotation does not align with the axis of the chamber; it is parallel to it and somewhat lower). Inlet and outlet ports are located in the flat endplates with their positioning being very important.
Product Download Operation In use, vacuum pumps are about half-full with liquid and the rotation of the impeller churns it into a vortex-type motion around the wall of the pumping chamber. The spinning liquid effectively seals the space between each pair of adjacent vanes into individual cells.

The cells vary in size as they rotate through a complete revolution. At the very bottom the length of the cell is equal to the radius of the chamber less the distance of eccentricity; at the top it is equal to the radius of the chamber plus the distance of eccentricity.

As a cell rotates upward from the bottom, its length increases which reduces the pressure within it. Conversely, on the second half of the rotation, the cell is descending and its length is reducing, which pressurises the cell.

The inlet port is located on the upstroke side of the rotation, so that the reducing pressure sucks fluid into the chamber. A short time later it is pumped out of the chamber through the outlet port located 180degs away on the downstroke side.

Liquid ring pumps are available as single-stage or double-stage units. Although theoretically possible, three- and more-stage units are rare. Typically, a two-stage pump has a single shaft and two aligned but separate compression chambers, each with its own impeller.