Page 244 - Intro Predictive Maintenance

Process Parameters 235

Table 10–10a 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 C

THE CAUSES Motor Over-Heating Starts Too Often
Air Discharge Temperature Too High
Air Fitter Defective
Air Flow to Fan Blocked
Air Leak into Pump Suction
Ambient Temperature Too High
Assembly Incorrect
Bearings Need Adjustment or Renewal
Belts Slipping
Belts Too Tight
Centrifugal Pilot Valve Leaks
Check or Discharge Valve Defective
Control Air Filter, Strainer Clogged
Control Air Line Clogged
Control Air Pipe Leaks
Crankcase Oil Pressure Too High
Crankshaft End Play Too Great
Cylinder, Head, Cooler Dirty
Cylinder, Head, Intercooler Dirty
Cylinder (Piston) Worn or Scored H L H L H H
Detergent Oil Being Used (3)
Demand Too Steady (2)
Dirt, Rust Entering Cylinder

10.4.3 Reciprocating Positive Displacement
Reciprocating compressors have a history of chronic failures that include valves, lubri-
cation system, pulsation, and imbalance. Table 10–10a to e identifies common failure
modes and causes for this type of compressor.

Like all reciprocating machines, reciprocating compressors normally generate higher
levels of vibration than centrifugal machines. In part, the increased level of vibration
is caused by the impact as each piston reaches top dead-center and bottom dead-center
of its stroke. The energy levels are also influenced by the unbalanced forces gener-
ated by nonopposed pistons and looseness in the piston rods, wrist pins, and journals
of the compressor. In most cases, the dominant vibration frequency is the second
harmonic (2X) of the main crankshaft’s rotating speed. Again, this results from the