Liquid Ring Pump – Main Principles and Features

A liquid ring vacuum pump is a gas vane pump that varies its working volume by immersing the rotor vanes in the liquid. In short, the liquid is pressed against the walls of the working cylinder by centrifugal forces, thereby receiving a rotational impulse from the rotor.

The principle behind the liquid ring pump was developed in 1890 and is known as a “water ring pump.” Due to their simple and reliable design, liquid ring pumps are suitable for generating vacuum in cases were removing firedamp or vapors or when condensation may occur inside the vacuum pump during the compression process. These devices are ideal for operation in a humid environment. They are typically used to generate a rough vacuum in various industrial processes, such as the chemical industry or in the production and refining of oil, as well as for the evacuation of steam turbine condensers and in the production of plastics and paper. In addition, such devices are widely used in the food industry and for many other industrial applications.

Operating Principle

The working fluid in a liquid ring pump is water or another liquid compatible with the pumped gas or steam. In addition, other liquids are often used:

• Ethylene glycol; 
• Mineral oils; 
• Organic solvents. 

The basic operating principle is identical for all units, regardless of size and design.

The eccentrically mounted impeller wheel rotates inside the cylindrical housing. The housing is filled with working fluid to the extent that the impeller blades are immersed in the liquid. The rotation of the impeller wheel and the resulting centrifugal force cause the liquid in the housing to form a liquid ring. As a result of the rotation of the impeller wheel, the volume of the gaps between the blades changes, leading to suction, compression, and gas ejection. The function of the liquid ring is that individual gaps are sealed to the cylinder. For this reason, the working fluid can be called a sealing fluid.

However, sometimes, it is necessary to clean it and pump liquids.

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The Liquid Ring Pump Mechanism

The presented devices use a working fluid, which allows this mechanism to be used only in a rough vacuum. The reason is that the required vacuum level depends on the vapor pressure and viscosity of the liquid with which the pump works. As a rule, pumps of this type operate in an isothermal mode. This means that the pumped medium is practically not heated during compression. Low temperatures in the presented pumps contribute to the condensation of process vapors and gases, so we can say that, to a certain extent, the vacuum pump functions as a condenser. In addition to condensation, an increase in the pumping speed is also observed. The working fluid removes the heat of compression, which helps condensation and increases the pumping speed. 

The main and important advantage of liquid ring pumps is the ability to adapt the working fluid and materials used in the components to the pumped medium. At the same time, the pump allows you to work with explosive gases and steam. Thanks to the low operating temperatures, pumping explosive materials can be much easier and safer than other types of vacuum pumps.

You can find a wide range of liquid ring pump for water. A liquid ring positive displacement pump with a star-shaped impeller provides the pump with significant suction capacity. Particularly suitable for pumping liquids, it can also be used for pumping volatile liquids.