Page 247 - Intro Predictive Maintenance

238 An Introduction to Predictive Maintenance

Table 10–10d Common Failure Modes of Reciprocating Compressors

THE PROBLEM

Air Discharge Temperature Above Normal Carbonaceous Deposits Abnormal Compressor Fails to Start Compressor Fails to Unload Compressor Noisy or Knocks Compressor Parts Overheat Crankcase Oil Pressure Low Crankcase Water Accumulation Delivery Less Than Rated Capacity Discharge Pressure Below Normal Excessive Comp

THE CAUSES Motor Over-Heating Starts Too Often
Pulley or Flywheel Loose
Receiver, Drain More Often
Receiver Too Small
Regulation Piping Clogged
Resonant Pulsation (Inlet or Discharge)
Rod Packing Leaks
Rod Packing Too Tight
Rod Scored, Pitted, Worn
Rotation Wrong
Runs Too Little (2)
Safety Valve Defective
Safety Valve Leeks
Safety Valve Set Too Low
Speed Demands Exceed Rating
Speed Lower Than Rating
Speed Too High
Springs Broken
System Demand Exceeds Rating
System Leakage Excessive
Tank Ringing Noise
Unloader Running Time Too Long (1)
Unloader or Control Defective

Each time the compressor discharges compressed air, the air tends to act like a com-
pression spring. Because it rapidly expands to fill the discharge piping’s available
volume, the pulse of high-pressure air can cause serious damage. The pulsation wave-
length, l, from a compressor with a double-acting piston design can be determined by:

60a 34 050
,
l = =
2n n
Where:

l = Wavelength, feet
a = Speed of sound = 1,135 feet/second
n = Compressor speed, revolutions/minute