Boiler and Auxiliary Technical Services
Industrial fan repairs, replacement, reconditioning and balancing
Frequently Asked Questions
- 1: Why aren't the bearings lasting as long as they used to - when the fan was new?
- 2: We installed a spare impeller and the unit vibrates just as badly/worse.. Why?
- 3: The bearings are getting hotter than they used to be. Why?
- 4: There is a rattling noise coming from the fan all the time. Where and Why?
- 5: There are noises that only happen when the fan gets to full speed. Why?
- 6: There are serious vibrations when the fan gets to full speed. Why?
- 7: The motor is noisy on start up, but quiet at full speed. What could cause that?
- 8: How much grease do we put in the bearings?
- 9: To which bearing do we fit the locating rings ?
- 10: The shaft is vibrating axially. Why?
- 11: The vee belts deteriorate quickly. What causes that?
- 12: We shut the fan down and all was OK. When we restarted it later, it vibrated. Why?
1a. The impeller is damaged or dirty
1b. The shaft is worn where the bearings fit
1c. The support frame/structure is loose/cracked
1d. The holding bolts are loose
1e. The pulleys and belts are worn
1f. The replacement bearings are incorrectly fitted/greased
2a. The spare impeller is not balanced
2b. The shaft is bent
2c. The pulley is unevenly worn
2d. The bearings or housings are faulty/worn/loose
3a. The bearing clearances are incorrect
3b. The bearings are over greased
3c. Direct sunlight intrudes on to the housings creating additional heat
3d. Insufficient ventilation local to the bearings
4a. Bolts are loose allowing movement
4b. Support frame/pedestal is cracked
4c. The casing has loose attachments
4d. Belt guard is loose/rubbing on belts
4e. Put hand on noisy area, see whether rattling stops.
5a. 'Out-of-balance' is too high
5b. Bearings are loose, allowing shaft movement
5c. Shaft is flexing at full speed
5d. Impeller is touching inside fan at full speed
6a. Clearances inside fan are small and rotor is touching inlet whilst running
7a. Belt tension is incorrect and overloaded at start up
7b. Motor non-drive end bearing housing is oval
8. If you have a grease escape hole in the housing, (a) manufacturers' recommendation (based on rotational speed) can be exceeded - even by
periodic addition via grease nipple in housing.
If there is no grease escapes hole in the housing, (estimate)
8a. Below 600rpm - three quarters full in housing
8b. Up to 1500rpm - half full in housing
8c. Faster than that - a quarter full in housing
Where continuous bearing failures occur, reasons of temperature, vibration, contamination, under/over greasing, bearing clearances and design parameters are all under review by your specialist bearing supplier.
9. (Where angels and fools fear to tread) If the fan is handling cold air, we would
9a. Locate the drive end when direct coupled
9b. Locate the fan end when belt driven
If the fan is handling hot air/gas, we would locate the drive end in both instances.
10a. No locating rings fitted in either bearing
10b. Locating rings incorrectly fitted
10c. Alignment is incorrect for pulley/coupling
11a. Motor mounted on separate base from fan
11b. Pulley alignment incorrect
11c. Belt tension too slack
11d. Too many starts - inadequate design
12a. Hot fan left standing allowed shaft to bend
12b. Contamination during standing time (from chimney or product) creates 'Out of balance'.
