Page 340 - Reciprocating Compressors Operation Maintenance

Troubleshooting Compressor Problems 325

This procedure also applies to the discharge valves, which, of course, will
be at a considerably higher temperature, 350°-375°F on a 100 psi single-
stage air compressor. In any event, it is recommended practice to look for
any valves exhibiting cover temperatures more than 15°F higher than usual,

Multistage compressors are designed so that the amount of work per-
formed per stage is exactly equal. In other words, a two-stage 100 BHP
compressor will require a 50 BHP per stage.
The correct pressure ratio across each stage is determined by formulas
employing absolute pressures:

2 Stage: 2I&- 3 Stage: 3 p-
5
1JP, ^Pi
Improper interstage pressures can cause problems with rod loads,
capacity, vibration, etc.
On multistage compressors, the interstage pressure should be checked
even before valve temperature readings are acquired. See page 25.

Low INTERSTAGE PRESSURE

On multistage compressors, intercooler pressure deviations will point
to the cylinder in which a problem is occurring. When a lower than nor-
mal interstage pressure is noted, a problem in the preceding cylinder, that
is, first stage of a two-stage compressor exists. If the interstage pressure
is low when the compressor is loaded and remains steady when
unloaded, the fault is in the suction valves of the preceding cylinder
(first-stage of a 2-stage compressor). Should the pressure drop to zero,
the discharge valves of the preceding cylinder are at fault.

HIGH INTERSTAGE PRESSURE

A higher than normal intercooler pressure indicates problems in the
succeeding cylinder, that is, second stage of a two-stage compressor.
Should the pressure be higher than normal when the compressor is
loaded, the suction valves of the succeeding cylinder are the problem. If
the intercooler pressure is higher when unloaded, the discharge valves in
the succeeding cylinder are at fault. If interstage pressure becomes too
high, the safety relief valve will blow.