MacGregor Screw compressors

Common issues

• Oil separator element fouling causing oil carryover into the starting air system
• Air/oil cooler fouling reducing cooling capacity
• Screw element bearing wear from oil degradation or contamination
• Minimum-pressure/non-return valve wear causing slow build-up or backflow
• Safety/unloader valve failure
• Moisture separator or drain trap blockage causing water carryover to receivers

Inspection checklist

• Discharge pressure and temperature trend
• Oil separator differential pressure
• Oil condition and level
• Safety valve function test
• Air/oil cooler cleanliness
• Automatic drain trap function on the compressor and receivers
• Unloader/capacity control valve operation
• Vibration and noise level
• Starting air receiver internal condition and drain
• Non-return valve condition at the receiver inlet

Service intervals

Typical wear limits

Ranges are typical for this design class. Always confirm against the manufacturer documentation for your serial number.

Critical spares

• oil separator element
• air filter element
• safety/relief valve
• non-return valve
• drain trap/solenoid drain valve

Safety

• Starting air receivers store significant energy - isolate and vent before opening any part of the system
• Hot discharge air and compressor casing surfaces
• Never exceed the receiver's rated working pressure; verify the safety valve set point against the receiver nameplate
• Rotating drive coupling guarding

Class survey

Starting air compressors and receivers are covered under machinery survey; class checks safety valve function, receiver internal condition/thickness where due, non-return valve condition, and automatic cut-in/cut-out function for maintaining starting air pressure.