Page 242 - Intro Predictive Maintenance

Process Parameters 233

Table 10–9 Common Failure Modes of Rotary-Type, Positive-Displacement Compressors

THE PROBLEM

No Air/Gas Delivery Insufficient Discharge Pressure Insufficient Capacity Excessive Wear Excessive Heat Excessive Vibration and Noise Excessive Power Demand Motor Trips Elevated Motor Temperature Elevated Air/Gas Temperature

THE CAUSES
Air Leakage Into Suction Piping or Shaft Seal
Coupling Misaligned
Excessive Discharge Pressure
Excessive Inlet Temperature/Moisture
Insufficient Suction Air/Gas Supply
Internal Component Wear
Motor or Driver Failure
Pipe Strain on Compressor Casing
Relief Valve Stuck Open or Set Wrong
Rotating Element Binding
Solids or Dirt in Inlet Air/Gas Supply
Speed Too Low
Suction Filter or Strainer Clogged
Wrong Direction of Rotation
Source: Integrated Systems, Inc.

levels. Common failures of this type of compressor occur with shaft seals, vanes, and
bearings.

Shaft Seals. Leakage through the shaft’s seals should be checked visually once a
week or as part of every data acquisition route. Leakage may not be apparent
from the outside of the gland. If the fluid is removed through a vent, the discharge
should be configured for easy inspection. Generally, more leakage than normal is
the signal to replace a seal. Under good conditions, they have a normal life of 10,000
to 15,000 hours and should routinely be replaced when this service life has been
reached.

Vanes. Vanes wear continuously on their outer edges and, to some degree, on the faces
that slide in and out of the slots. The vane material is affected somewhat by prolonged
heat, which causes gradual deterioration. Typical life expectancy of vanes in 100psig
service is about 16,000 hours of operation. For low-pressure applications, life may
reach 32,000 hours.