Fan Doctor

Most industrial fans are very reliable, designed by knowledgeable manufacturers for long life under a multitude of conditions; however, breakdowns do happen. They can be caused by incorrect installation, lack of maintenance, improper fan selection, or years of strenuous service may have simply worn out the fan.

For more complex causes and remedies please click on the Fan Doctor section and complete the request. Your request will be answered promptly by a qualified Chicago Blower service technician.

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Cause Remedy
Most common cause of vibration is an out of balance fan wheel Out of BalanceCheck the wheel for any dirt or foreign material, especially in hard-to-see places: backside of the wheel, underside of the blades.

Airfoil blades are usually hollow, and when exposed to excessive moisture can retain water. Drill a 3/16" drain hole near the trailing edge to fix the problem. Rebalancing is not usually necessary.

Check for corrosion or erosion, which usually occurs on the nose of the blade. On a paddle wheel fan the blade tips may be worn. An airfoil wheel exposed to abrasive material can develop pin holes in the nose of the blades. Eliminate these conditions and rebalance the wheel. If the wheel is seriously damaged, it will have to be replaced.
Improper or loose mounting Make sure foundation bolts are tight.
Loose wheel-to-shaft screws Tighten the screws, but first be certain the wheel hasn't shifted on the shaft or is rubbing on the inlet cone or drive side of the housing.
Bent fan shaft Check the shaft with a dial indicator. If bent, replace as soon as possible to avoid replacing the entire fan.
Misaligned V-belt drive, common problem on belt driven fans Motor ShaftRealign assembly so fan and motor shaft are parallel and faces of sheaves (pulleys) are flush to a straight edge. A taut string will work.
Wheel turbulence due to rotor running backwards Check for correct wheel rotation, clockwise or counter clockwise, as seen from the drive side.
Air pulsation If the fan is operating in the stall area of its performance curve it may be oversized or the system resistance is higher than intended. You can lower the system resistance by cleaning the filters or opening the dampers.
Cause Remedy
Foreign material in the fan housing Inspect the wheel and inside of fan housing and clean thoroughly.
Squealing V-belts Belts are either loose or misaligned. If belts show wear, replace them now to avoid a future breakdown.
Worn ball or roller bearings. (Howling, screeching, or clicking) Change the bearings immediately before they cause additional damage. Failing bearings tend to wear the shaft, make sure the shaft is full size before installing new bearings. "Mike" the shaft both under the bearing and next to it and compare the two readings. If they do not match, replace the shaft. New bearings installed on a worn shaft will not last long.
Bearing seal misaligned. (High pitch squeal) Bearing SealRealign the face of the bearing so that it is perpendicular to the shaft.
Metal shaft seal misaligned and rubbing on the shaft Loosen seal plate bolts, re-center the seal on the fan shaft and tighten the bolts. If the seal is fiberglass, cork or rubber, be sure the metal backing plate does not touch the shaft.

Ball or roller bearings tend to heat up when they have been over greased and will cool down when the excess grease oozes out. The normal operating temperature of a bearing may be well above 140F. Use instruments to read the temperatures. Anything above 180F should be questioned. If you place a water drop on the bearing and it sizzles, the bearing is in distress and should be changed before it seizes and ruins the shaft.

Cause Remedy
Bearing may be worn and failing Replace the bearings. Remember to also check the shaft. (refer back to Noise section)
Improper grease Use a lithium base, high speed, channeling type grease. Do not use high temperature or general purpose grease.
Over greasing Running the bearing for a few hours will normally purge itself of extra grease. You can simply remove excess grease from split roller bearings by lifting the top half of the block for access.
Bearing exposed to "heat soak" from an oven or dryer after shutdown. "Heat soak" occurs when a fan is idle and its shaft cooling wheel can no longer cool the inboard bearing. Heat from inside the fan can actually cook the grease. A 15 minute fan run after the oven heat is turned off will cool the fan shaft and protect the bearing.
Loose V-belts may cause belt slippage and friction resulting in hot bearings, shafts or sheaves V-beltsTighten belt to proper tension. A good rule of thumb - you should be able to depress the belt the same distance as the thickness of the belt.
Excessive V-belt tension Belts may be too tight. Adjust to the correct tension
Cause Remedy
Fan rotation incorrect Refer to Vibration section. An easy way to change rotation on most 3-phase motors is to reverse any two motor leads.
Abrupt turn in the duct close to the fan discharge or air pre-spin caused by ductwork elbows at the inlet Install turning vanes or elbow splitters in the duct. If air performance is still inadequate, the discharge position may have to be changed.
Improperly installed Inlet Volume Control (IVC) Inlet Volume ControlIf fan has an IVC be sure the IVC is installed with pre-spin of the air in direction of wheel rotation when the IVC is partially closed.
Off-center wheel This can occur on double width, double inlet fans. Center the fan between the inlet cones to avoid overloading one side of the wheel while starving the other.
Fan horsepower unexpectedly low Correct one or more of the following conditions:
  • Air pre-spin into the fan inlet
  • Fan drive sheaves set for too low a fan speed
  • Resistance to airflow, such as caused by a closed damper, much higher than calculated
Fan horsepower unexpectedly high Correct one or more of the following conditions:
  • Be sure fan speed is not too high. Fan may be operating without ductwork at low resistance so that too much air is flowing.
  • The fan may be handling ambient air when it was originally intended for hot, less dense air.
  • Fan may be running backwards

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