Page 248 - Intro Predictive Maintenance

Process Parameters 239

Table 10–10e 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
Unloader Parts Worn or Dirty
Unloader Setting Incorrect
V-Belt or Other Misalignment
Valves Dirty
Valves Incorrectly Located H L H L H H
Valves Not Seated in Cylinder H L H L H H
Valves Worn or Broken H L H L H H H H
Ventilation Poor
Voltage Abnormally Low
Water Inlet Temperature Too High
Water Jacket or Cooler Dirty
Water Jackets or Intercooler Dirty
Water Quantity Insufficient
Wiring Incorrect
Worn Valve on Good Seat
Wrong Oil Type
(1) Use Automatic Start/Stop Control
(2) Use Constant Speed Control
(3) Change to Non-Detergent Oil
H (in High Pressure Cylinder)
L (in Low Pressure Cylinder)

For a double-acting piston design, a compressor running at 1,200 revolutions per
minute (rpm) will generate a standing wave of 28.4 feet. In other words, a shock load
equivalent to the discharge pressure will be transmitted to any piping or machine
connected to the discharge piping and located within 28 feet of the compressor. Note
that, for a single-acting cylinder, the wavelength will be twice as long.

Imbalance
Compressor inertial forces may have two effects on the operating dynamics of a rec-
iprocating compressor, affecting its balance characteristics. The first effect is a force
in the direction of the piston movement, which is displayed as impacts in a vibration
profile as the piston reaches top and bottom dead-center of its stroke. The second effect
is a couple, or moment, caused by an offset between the axes of two or more pistons