Liquid ring pump
A liquid ring pump (also called a water ring pump , liquid ring vacuum pump or liquid ring compressor) is used to convey and compress gases , which is why, technically speaking, it is actually not a pump, but a compressor . It is often used as a vacuum pump , especially in plant and process technology, for example in the chemical industry . As a liquid ring venting pump , it is used by the fire service to vent the suction line for pumping water from open waters.
Functional principle of a liquid ring pump
In the cylindrical housing of the liquid vacuum pump there is a star-shaped, eccentrically arranged impeller / impeller. The liquid contained in the housing (normally water) forms a liquid ring concentric to the housing when rotated by centrifugal force , which seals the impeller chambers. Impeller and housing do not touch each other, sparking is not possible. Due to the eccentricity, the blades are immersed in the liquid ring at different depths: The ring acts like a piston that alternately sucks and compresses. There are also designs with an 8-shaped housing (double eccentricity) in which the impeller sits centrally in the housing. In the covers, which laterally seal the impeller, there are recesses, so-called side channels, into which the liquid ring is pressed and thus the eccentric geometry that is required to generate the pressure difference between the individual chambers is created.
The operating fluid has 4 functions:
- Sealing
- no contact between impeller and housing (no lubrication, no sparking)
- compression
- Ring segment acts as a piston (sucks and compresses between the blades through eccentricity)
- Cool
- the compression is isothermal (the specific heat of the operating fluid is much higher than that of the gas)
- Condense
- the vapors are condensed at the inlet and the pumping speed of the volumetric pump is improved
The pumping speed of the liquid ring pump is reduced by the proportion of the saturation vapor pressure in the suction pressure, which is why the suction pressure of the liquid ring pump cannot fall below the saturation vapor pressure of the operating fluid used. The compression and condensation heat generated during compression is dissipated via the operating fluid. This is often returned as an external circuit from the pressure side to the suction side and is cooled with a heat exchanger.
advantages
- the formation of sparks through contact between metals is prevented due to the operating fluid used; liquid ring pumps are therefore suitable for conveying and compressing explosive gas mixtures
- Insensitive to liquids / steam and solid particles
- Isothermal compression (high efficiency, can be used for products that tend to polymerize or disintegrate at high temperatures)
- Oil-free compression (no contamination)
- High level of safety for the compression of ignitable gases and vapors (sealing with the operating fluid)
- Simple design for corrosion-resistant materials
- Insensitive to the conveyance of solid particles or fibers
- Can also be used as a washer
- Can also be used as a capacitor
- Relatively quiet and low-vibration operation
- No maintenance (only on the shaft seal)
disadvantage
- High power consumption due to the friction losses
- The gas to be pumped is saturated with operating fluid at the outlet
- Needs an operating fluid or cooling of the operating fluid
- Maximum achievable vacuum limited (up to max. Approx. 30 mbar abs with water as the operating fluid or approx. 10 mbar abs with other liquids)