19th Sep. 05

This type is the 'Stall's' screw compressor for A/C system.

In dry dock we renewed both evaporators and the system was commissioned. It was running safely for two days, the third day one compressor was cutting off frequently due to over load.

The compressor was changed over, system isolated and compressor dismantled. We found that the rotor was damaged and bush bearings were damaged completely.

While we were assessing the problem the other compressor also failed in similar fashion. Meanwhile we received a new compressor. But before fitting it we felt compelled to find the cause of failure.

The compressor is lubricated by the difference of pressure (suction & discharge) and no lube oil pump is provided. It was observed that it supplies sufficient lubrication to suction side of the rotor where the suction pressure is less, but when it came to discharge side of rotor it was giving very less lubrication; just enough to lubricate the bush bearings.

When the evaporator was changed, the old expansion valves were not adjusted, so it was supplying liquid to the compressor which froze the lube oil and increased line friction that eventually lessened the lube oil flow and caused the bearing & rotor failure. The expansion valves were adjusted and the system commissioned.