Page 37 - Reciprocating Compressors Operation Maintenance

24 Reciprocating Compressors: Operation and Maintenance

tOO 200 300 400 500 800
Discharge pressure — psig

FIGURE 1-14. Comparative theoretical adiabatic horsepower per 100 cfm
required for single- two-, and three-stage compression.

The desirability of imposing a maximum temperature limitation is not
always fully appreciated. This applies particularly to air compressors
where oxidizing atmospheres exist and where lubricating oil decomposi-
tion accelerates as temperatures rise. Actual discharge temperature will
vary to some degree from the theoretical adiabatic, depending upon com-
pressor size, design, method of cooling, and compression ratio. No rules
can be set, but the deviation is not apt to be serious, and the theoretical
limitation is an excellent guide.
A compressor in continuous heavy-duty service should definitely be
designed more conservatively regarding discharge temperature than one
operating on a relatively light or intermittent cycle.
As discharge temperatures go up, downtime and relative maintenance
costs will certainly increase.
As a guide, for medium and large heavy-duty compressors (around
150 bhp and larger) handling air or any other oxidizing gas, the maxi-
mum discharge temperature should not exceed 350°E For pressures over
300 psig, this temperature should be further scaled down.

INTERSTAGE PRESSURES

Actual interstage pressure readings are valuable indicators of the rela-
tive tightness of valves and piston rings and should be checked several