Liquid Ring Vacuum Pump

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A pump that is actually not a pump: Liquid ring vacuum pumps are compressors that are perfectly suited for conveying critical gases and gases charged with liquid droplets. In the vacuum they convey gases, not liquids.

These rotating displacement pumps are as varied as their name: The liquid ring vacuum pump is also known as the water ring pump, liquid ring compressor, or simply the liquid ring pump. These pumps are used in the chemical and petrochemical industries, in the pharmaceutical industry, and for the manufacturing of colors and paints, as well as in general system and machine construction.

vacuum pump

Delivery characteristics of the Liquid Ring Vacuum Pumps from our alliance members


Capacity [Q]: max. 3000 m³/h

Discharge pressure: max. 2500 mbar (abs)

Pressure Rating: PN 10

Temperature: -20 °C to +100 °C

How a liquid ring vacuum pump works

The liquid ring vacuum pump consists of a cylindrical housing and a star-shaped, eccentrically arranged impeller. The pump’s working space is frequently filled with operating liquid during operation, normally with water. When the impeller turns, the liquid forms a liquid ring that seals the impeller channels even though these do not touch the housing. The eccentrically arranged blades penetrate at different depths into the liquid ring. This ring then works like a piston, by alternately sucking in and compressing the gas.

In addition to acting as a seal, the liquid ring also takes over the compression function. Furthermore, it can be used to cool and condense the conveyed gas. The condensing increases the suction power of the liquid ring vacuum pump.

Thanks to a flexible pressure slot in the control disk, the liquid ring vacuum pump works with maximum efficiency across the entire suction range. The pressure slit opening created this way adjusts to the existing pressure relations so that there is no excessive compression of the conveyed gases.

Depending on the size, single-stage displacement pumps are equipped with single or double-bladed impellers. The special features here are that the pumps do not need to be lubricated and there are no components touching each other in the conveying chamber. This is why these pumps distinguish themselves with their quiet, low-vibration operation and their simple, robust construction.

The operating principle of a liquid ring pump is similar to that of a rotary vane pump. Instead of fixed blades, however, the rotary vane pump has vanes that are also sealed off from the housing by a liquid ring.

Are liquid ring pumps actually pumps or are they compressors?

Essentially, there are several different kinds of machines for handling media: pumps that convey liquids, and compressors and blowers that transport gases. According to this distinction, the principle of the liquid ring vacuum pump makes it a compressor.

As with an air pump for bicycle tires, which pumps air as a gas mixture, the term liquid ring vacuum pump extends back to the piston vacuum air pump. It was invented by Otto von Guericke in 1649 and served to pump air out of a closed container, which produces a vacuum.

Applications, Benefits & special features of liquid ring vacuum pumps

Areas of applications

Liquid ring vacuum pumps are used primarily for evacuating moist gases and vapors that already have to be condensed during the compression process. Since their compression is nearly isothermal, these machines are especially well-suited for handling explosive gases and vapors and those that tend toward polymerization.

Applications of this type are in demand especially in the chemical and petrochemical industries; in pharmaceutical manufacturing; in the manufacturing of colors and paints; and generally in construction and mechanical engineering. Typical media are air (O2), nitrogen (N), carbon dioxide (CO2), water vapor or solvent vapors. For critical media, models with a hermetic shaft seal with magnetic coupling are available. Due to their operating principle, liquid ring vacuum pumps are well-suited for use in areas subject to explosion (up to Ex Zone 0) since the operating liquid not only cools, but also prevents the formation of sparks.

A maximum vacuum of approximately 30 bar (abs) can be achieved with this type of vacuum technology. Lower suction pressure can be achieved with multi-stage models, for example with upstream gas and steam jets or vapor ejector pumps. Depending on the design, the technology for vaporization pressure can be used up to approximately 2,500 mbar (abs); in special cases up to 6 bar.

Benefits and special Features

Even with common designs using metal elements, the fluid inside the pump prevents spark formation. In addition, the conveyed gas can be charged with liquids, solid particles, and fibers.

The isothermal compression of liquid ring pumps offers great efficiency. In addition, it promotes use with media that tend toward polymerization or that decay at high temperatures. Thanks to the vacuum technology with oil-free compression, there is no contamination of the conveyed fluid.

The liquid ring pumps can have no parts that touch one another, which provides quiet and low-vibration operation. They are also low-maintenance; only the shaft seal and auxiliary units require attention. With their simple design, these compressors can also be used as washers and condensers.

Broad spectrum of use – also for your application

When gas conveyance is the concern, liquid ring vacuum pumps are the first choice in many industries, and they are often indispensable. They distinguish themselves through their numerous benefits and application possibilities.

Does your application require a liquid ring vacuum pump? Send us your inquiry and we will perform a non-binding check right away.

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