DETECTION AND REMEDY OF REFRIGERATION COMPRESSOR / MOTOR MISALIGNMENT

Detection of misalignment

1. Visual/rough check: with the coupling guard removed; a straight-edge across the two coupling halves (rims) will show angular misalignment; feel for unequal gaps around the circumference (face misalignment) and difference in radial position.
2. Feeler gauge and dial test indicator (DTI) method: Mount a dial indicator on one coupling half (rigidly) with the plunger bearing on the face and rim of the other half; rotate slowly and record total indicator reading (TIR). Radial TIR indicates parallel offset misalignment; face (axial) TIR indicates angular misalignment. Take readings at top, bottom and sides (0,90,180,270 deg) and at each 90 deg position to get a full picture.
3. Laser alignment (modern preferred method): A belt-driven or flange alignment laser kit (e.g. on motor-pump sets) measures accurate offset and angular values in both vertical and horizontal planes and gives shim/ moves. This is the most accurate for a large reciprocating compressor.
4. Operational symptoms of misalignment: excessive vibration, noise, overheating of the coupling/ bearings, rapid motor or compressor bearing wear, high current/amps, coupling wobble, or oil leakage; misalignment often shows as vibration at 1x rpm and as a machine that is hot but not overloaded.

Remedy

1. Stop the crane and isolate (electrical and mechanical), lock off, and remove the coupling guard.
2. Slacken the motor hold-down (foundation) bolts.
3. Using a dial/ laser alignment procedure, adjust the motor (or compressor) by shims (parallel shimming) to remove the vertical offset and angular misalignment, and move/pack to correct horizontal (side) misalignment.
4. Set the correct face gap (distance between coupling halves) to the maker's coupling specification, and correct the coupling to the machine's cold-alignment figures (accounting for thermal growth at operating temperature where specified).
5. Re-torque the foundation bolts evenly in sequence.
6. Re-check the alignment with the dial/laser and re-adjust until TIR is within manufacturer tolerance.
7. Re-fit the coupling (if split/removed), refit bolts/screws of the coupling to the correct torque, then refit the guard.
8. Record the alignment figures in the maintenance record for future reference and set a schedule to re-check alignment, especially after bedding-in or foundation work.

Note: If a large alignment change is required, also check the machine feet/foundation for soft-foot (using the dial/ laser to detect a resilient/ low foot) and pack accordingly, as soft-foot will distort the frame and cause repeat misalignment.