TL;DR
Rising vibration on a screw compressor bearing signals imminent failure. Take an oil sample, trend the vibration readings, and schedule a bearing inspection at the next opportunity.
What you might see
- vibration level increasing at compressor housing
- bearing temperature rising at drive end
- unusual rumbling or rotor noise
- oil analysis showing metallic particles
Likely causes
Oil contamination from moisture or refrigerant causing bearing surface pitting
Bearing fatigue after extended operating hours
Rotor imbalance from refrigerant liquid slug damage to rotor lobes
Misalignment at the motor-to-compressor coupling
Required tools
- Vibration meter with trend logging
- Oil sample kit
- Dial indicator (for coupling alignment)
- LOTO kit
Safety first
- Screw compressors in ammonia service require a qualified refrigeration mechanic for any work involving the refrigerant-side bearings.
- High vibration on a running compressor can cause sudden rotor contact. Do not delay action if vibration exceeds the shutdown setpoint.
- Lock out the compressor before accessing the coupling or drive-end bearing housing.
Procedure
- 1
Take baseline vibration readings at the drive-end and non-drive-end bearing housings using a vibration meter. Record velocity in mm/s.[1]
- 2
Trend the readings weekly. A rising trend is more significant than a single high reading.[1]
- 3
Take an oil sample for analysis. Submit for particle count, viscosity, and refrigerant contamination. Metallic particles indicate active bearing wear.
- 4
Check the coupling alignment between the compressor and the drive motor. Misalignment drives radial bearing load.
- 5
Review the oil change history and oil analysis trend. Oil degradation accelerates bearing wear.
- 6
If velocity above 7 mm/s or oil analysis shows heavy metallic contamination, plan an immediate bearing inspection.
- 7
Coordinate with the refrigeration maintenance team to plan a shutdown for bearing inspection without a prolonged loss of refrigeration capacity.
Sources
Frick (Johnson Controls) Frick RWB / RXF screw Industrial Refrigeration / Blast Freezer general technical documentation, Frick (Johnson Controls)
Frick RWB / RXF screw compressor general bearing maintenance and vibration monitoring procedures (general)
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