Fan Failures: Five Common Issues and Their Causes

Fan Failures: Five Common Issues and Their Causes

Centrifugal fans and fan systems used in industrial HVAC applications can fail in a variety of ways. Understanding the causes of these failures is helpful for troubleshooting. Marcel Kamutzki, Engineering Manager at Daltec Canadian Buffalo Manufacturing Ltd., a fan and blower manufacturer based in Guelph, Ontario, detailed five common failures and their symptoms at a maintenance professionals’ seminar in Hamilton. 1. Excessive fan noise. This may occur when the impeller strikes the inlet or housing, indicating that the impeller is not centered; the inlet or housing is damaged; the impeller is bent or damaged; there is a loose shaft or loose bearings; the shaft is bent; or the shaft and bearings are misaligned. If the impeller strikes the stop, it indicates that the stop is not securely fastened in the housing, is incorrectly positioned, or is damaged. If the problem lies with the belt drive, there are many possible causes: the pulley is not tight on the shaft; the belt is hitting the belt guard; the belt is too loose or too tight; the belt cross-section is incorrect; the belt lengths on a multi-belt drive do not match; variable-pitch pulleys have not been adjusted so that each groove has the same pitch circle diameter; the pulleys are misaligned or the belt is worn; the motor mount, base, or fan is loose; improper drive selection; a loose key; or a belt contaminated with oil or dirt. Possible causes of coupling issues include a loose or unbalanced key, misalignment, or a loose or improperly lubricated coupling. Bearing noise is caused by defects, loose supports, insufficient lubrication, a loose shaft, misaligned seals, foreign objects, or fretting corrosion between the inner ring and the shaft. When a shaft seal emits a squeaking sound, the culprit may be insufficient lubrication, misalignment, or a bent shaft. Impeller noise may be caused by defects, looseness, imbalance, or excessive wear on the shaft, or by corrosive materials moving through the flow passages or blades rotating close to structural components. Motor symptoms include unsafe cable entry, an AC humming sound in the motor or relay, a flickering starter relay, noisy motor bearings, a cooling fan striking the guard, or low voltage and single-phase operation in a three-phase motor. If the symptom is high air velocity, possible causes include a duct system that is too small for the application, a fan that is too large, a damper or grille that is too small, or insufficient surface area of the heating or cooling coils. When obstructions cause rattling or whistling, the cause may be dampers, sharp elbows, sudden expansion or contraction of the duct system, duct system leaks, rotating blades, or fins on the coils. Pulsation or surging can be traced to a restricted system causing the fan to operate on the left side of the peak, a fan that is too large for the application, ducts vibrating at the same frequency as the fan pulsation, distorted inlet flow, inlet vortex surging, or rotational stall. Creaking or rumbling noises are caused by a vibrating duct system, vibrating cabinet components, or vibrating components that are not isolated from the building structure.