The plant air system depends on four 100-hp motors, and one of them is vibrating badly. The pipe coming off the compressor even makes a rattling sound. What should you not do to solve this problem? What steps should you take?
Don’t put a wrench on those mounting bolts and start cranking. Your first step is to measure the level of vibration so you have "as-found" data. Then, check the alignment (motor to load). If the alignment is off, realignment may fix the problem. If the problem persists post-alignment, it’s time to "divide and conquer."
Decouple the motor from the load. Run the motor and measure vibration. If the vibration persists:
- Inspect the motor pedestal and base for cracks and warping.
- Compare the size and construction of the pedestal and base to those of the motors that don’t vibrate.
- Turn the shaft by hand, and feel for binding. Listen for bearing noise. Measure shaft run-out (check for bent shaft).
- Perform the other recommended tests (power supply, bearing noise, bonding, etc.).
- If you can’t find the problem with the motor in place, then send it to your motor shop for balancing and other appropriate tests.
- Inspect the coupling.
- Recouple the motor and align.
- Decouple the compressor from its load, and run vibration testing again (contact the manufacturer before conducting this test).
Here's a list of some problems as noted in actual case histories:
- Receiver drain valve was closed, causing water to accumulate and flow into trunk line.
- Pipes were forced into position during installation, causing torsion on the mounting flange at the compressor.
- Hydrostatic testing flange was inadvertently left in pipe. This flange was required for acceptance testing but never removed. Consequently, the compressor dead-headed into a closed pipe instead of the plant air network.