Page 135 - Root Cause Failure Analysis

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COMPRESSORS

A compressor is a machine used to increase the pressure of a gas or vapor. Compres-
sors can be grouped into two major classifications: centrifugal and positive displace-
ment. This chapter provides a general discussion of these types of compressors.

CENTRIFUGAL
In general, the centrifugal designation is used when the gas flow is radial and the
energy transfer is predominantly due to a change in the centrifugal forces acting on
the gas. The force utilized by the centrifugal compressor is the same as that utilized by
centrifugal pumps.

In a centrifugal compressor, air or gas at atmospheric pressure enters the eye of the
impeller. As the impeller rotates, the gas is accelerated by the rotating element
within the confined space created by the volute of the compressor’s casing. The gas
is compressed as more gas is forced into the volute by the impeller blades. The pres-
sure of the gas increases as it is pushed through the reduced free space within the
volute.

As in centrifugal pumps, there may be several stages to a centrifugal air compressor.
In these multistage units, a progressively higher pressure is produced by each stage of
compression.

Configuration
The actual dynamics of centrifugal compressors are determined by their design. Com-
mon designs are overhung or cantilever, centerline, and bullgear.

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