Is your equipment considered a slow-running speed machine? If so, what speed do you consider slow? Is it 30 RPM? 60 RPM? 100? 200? 600?
No matter what you consider slow speed, the two most critical points to consider for slow running equipment are:
1) Does your vibration sensor (accelerometer) have the appropriate frequency range to measure low frequencies?
2) Does your vibration analyzer and/or online monitoring system measure down to those frequencies?
Unfortunately, some vibration analysis devices on the market are not truly capable of measuring slow-speed equipment and providing a true mechanical diagnostic analysis. These devices can actually create a reactive maintenance result that the device was supposed to prevent.
For example, a motor shop in South Texas had completed a rebuild of a 100 HP motor. The motor is used in the oil and gas industry. It has an average running speed of 30 RPM. The customer tested the motor on their motor test stand. As it was in its test cycle, the vibration was measured using a self-diagnostic vibration analyzer. The results and diagnostics the analyzer provided to the customer were “please replace bearing”. After several further tests running the motor on the test stand, the customer refused to accept those results and retested the motor using a VIBXPERT® II analyzer with machine templates designed for slow running machinery and a VIB 6.147 low-frequency accelerometer.
The final analysis revealed a high unbalance condition on the motor (11 mils peak-peak). The motor shop followed up with a balancing job (single plane) on the motor. The balancing was performed with the VIBXPERT II as well. Subsequent tests showed that the unacceptable low-frequency amplitude that had been observed (11 mils pk-pk) prior to performing the balance job had now disappeared. Final mechanical diagnostics showed no problems and the bearings were in proper condition. A balance report was printed and the motor was ready to leave the shop.
If you want to increase your uptime and availability and reach your financial goals, proper investment in Condition Monitoring and reliability will provide a positive return on your investment.
Balancing, Maintenance Tips, Vibration Analysis by Alex Nino CRL