Commissioning and Alignment
What the exam tests
Commissioning tests preparation, safety checks, rotation, alignment, run-in, load testing, and documentation. Alignment questions use dial indicators or laser systems and expect you to correct angular and parallel misalignment without introducing soft foot.
Core rules
- Pre-commissioning checks include insulation resistance, rotation direction, guard fitment, lubrication, valve line-up, instrument calibration, and emergency stops.
- Bump-test a motor uncoupled where practicable. Confirm direction before connecting the driven machine.
- Measure soft foot first: loosen one foot at a time and check for movement or shim change. Correct it before coupling alignment.
- For angular misalignment, correction is proportional to distance: shim change = indicator reading × correction distance / indicator radius.
- Account for thermal growth. Align cold machines to the specified cold offset, not necessarily to zero.
Worked example
A dial indicator at a 100 mm radius reads 0.12 mm angular misalignment at the coupling. The angle is 0.12/100 = 0.0012 rad, or about 0.069°. To correct at a motor foot 400 mm from the coupling centre, the shim change is 0.12 × 400/100 = 0.48 mm. Add or remove that amount according to the sign, then recheck parallel offset and soft foot.
Traps
Aligning before removing pipe strain; ignoring thermal growth; correcting angular error without rechecking parallel offset; using the wrong indicator radius; and accepting a motor that runs but draws high current because rotation was never verified.