Page 146 - Root Cause Failure Analysis

134 Root Cause Failure Analysis

Figur *e 10-8 Liquidseal ring rotary air compressor (Gibbs 1971).

Liquid-ring compressors are cooled directly rather than by jacketed casing walls. The
cooling liquid is fed into the casing where it comes into direct contact with the gas
being compressed. The excess liquid is discharged with the gas. The discharged mix-
ture is passed through a conventional baffle or centrifugal-type separator to remove
the free liquid. Because of the intimate contact of gas and liquid, the final discharge
temperature can be held close to the inlet cooling water temperature. However, the
discharge gas is saturated with liquid at the discharge temperature of the liquid.

The amount of liquid passed through the compressor is not critical and can be varied
to obtain the desired results. The unit will not be damaged if a large quantity of liquid
inadvertently enters its suction port.

Lubrication is required only in the bearings, which generally are located external to
the casing. The liquid itself acts as a lubricant, sealing medium, and coolant for the
stuffing boxes.

Per$ormance
Performance of a rotary positive-displacement compressor can be evaluated using the
same criteria as a positive-displacement pump. Also refer to the previous discussion
of the laws of thermodynamics that apply to all compressors. As constant-volume
machines, performance is determined by rotation speed, internal slip, and total back
pressure on the compressor.

The volumetric output of rotary positive-displacement compressors can be controlled
by changing the speed. The slower the compressor turns, the lower is its output vol-