Boiler and Auxiliary Technical Services

Industrial fan repairs, replacement, reconditioning and balancing

PO Box 689, Pinetown,

3600, South Africa

+27 31 700 2731

+27 31 700 6684 fax

Frequently Asked Questions

  • 1: Why aren't the bearings lasting as long as they used to - when the fan was new?
  •   answer »« less

    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

  • 2: We installed a spare impeller and the unit vibrates just as badly/worse.. Why?
  •   answer »« less

    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

  • 3: The bearings are getting hotter than they used to be. Why?
  •   answer »« less

    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

  • 4: There is a rattling noise coming from the fan all the time. Where and Why?
  •   answer »« less

    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.

  • 5: There are noises that only happen when the fan gets to full speed. Why?
  •   answer »« less

    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

  • 6: There are serious vibrations when the fan gets to full speed. Why?
  •   answer »« less

    6a. Clearances inside fan are small and rotor is touching inlet whilst running

  • 7: The motor is noisy on start up, but quiet at full speed. What could cause that?
  •   answer »« less

    7a. Belt tension is incorrect and overloaded at start up
    7b. Motor non-drive end bearing housing is oval

  • 8: How much grease do we put in the bearings?
  •   answer »« less

    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: To which bearing do we fit the locating rings ?
  •   answer »« less

    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.

  • 10: The shaft is vibrating axially. Why?
  •   answer »« less

    10a. No locating rings fitted in either bearing
    10b. Locating rings incorrectly fitted
    10c. Alignment is incorrect for pulley/coupling

  • 11: The vee belts deteriorate quickly. What causes that?
  •   answer »« less

    11a. Motor mounted on separate base from fan
    11b. Pulley alignment incorrect
    11c. Belt tension too slack
    11d. Too many starts - inadequate design

  • 12: We shut the fan down and all was OK. When we restarted it later, it vibrated. Why?
  •   answer »« less

    12a. Hot fan left standing allowed shaft to bend
    12b. Contamination during standing time (from chimney or product) creates 'Out of balance'.


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