Page 38 - Reciprocating Compressors Operation Maintenance

Reciprocating Compressors and Their Applications 25

times daily. Any variation from normal operating pressures is cause for
immediate concern and investigation.
Since cylinder sizes for any multistage compressor are proportioned
for definite intake and discharge temperature and pressure conditions,
variations from design first-stage inlet pressure and temperature, as well
as changes in final discharge pressure and in cooling water temperature,
will cause interstage pressures to vary slightly.
In some cases, theoretical approximations are helpful. The following
may be used:

Two STAGE

Pj is first-stage intake — psia
P 2 is intercooler — psia
P 3 is second-stage discharge — psia

THREE STAGE

P } is first-stage intake — psia
P 2 is first intercooler — psia
P 3 is second intercooler — psia
P 4 is third-stage discharge — psia

Because of variation in cylinder proportions and clearances in an actu-
al compressor, the theoretical approach, with its equal compression ratios
per stage, cannot be considered to be completely accurate. Actual read-
ings from the specific machine, when in good condition and operating at
design conditions, should be considered the standard for reference.

EFFECT OF ALTITUDE

The altitude at which a compressor is installed must always be given
consideration. As altitude above sea level increases, the weight of the