Principles of Operation
Both the liquid ring and rotary vane depend on an eccentrically mounted rotor. In the case of the vane, blades slide in and out during rotation forming a seal with the housing bore. The liquid ring depends on a motive liquid, typically water, to form a seal during rotation. Both technologies reduce the volume of the gas during rotation by virtue of the eccentric rotor.
Compressed gas is discharged at the point of smaller displacement yielding compression. Rotary vanes wear by design and maintain their efficiency by sliding vanes always mating with the bore. Liquid ring vanes wear and result in continuously decreasing efficiency.
- Ro-Flo sliding vane compressors are capable of inlet pressure to 28″ Hg vacuum (5 kPa absolute), discharge pressures up to 150 psig (10.2 barg), and pressure ratios up to 7:1.
- Liquid ring compressors (LRC) are vacuum capable with varying discharge pressure and pressure ratios up to 4:1.
- Rotary vanes are not sensitive to high inlet pressure. Liquid rings are not tolerant of high inlet pressure.
- In similar service, rotary vane compressors require 1/2 the input power (or less) of a liquid ring compressor.
- The compression seal of a liquid ring could present slightly less “blow-by” of process gas.
- Liquid rings require filtration of motive liquid, often in several stages, and require considerable make-up liquid.
- The efficiency of a liquid ring compressor is affected by gas inlet temperature.
- Rotary vanes use a small quantity of lubricant injected directly to critical points during operation, including the compression chamber.
- Rotary vane lubricant is usually coalesced and captured downstream of the compressor.
- Liquid rings do not require lubricant injection into the compression chamber as the motive liquid seal keeps vanes separated from the housing.
Liquid ring technology presents a clear advantage in tolerance for liquid ingestion. Rotary vane technology presents significant advantages in reduced capital cost, reduced operational cost, lower maintenance cost and higher operational reliability. Rotary vanes present a very small amount of lubricant waste while liquid rings can present increased waste water treatment expense and makeup water expense. Compared to a good inlet scrubber, liquid rings present an expensive, complex alternative and rotary vanes are the lower cost, more reliable choice within their performance range.