Fan Troubleshooting

Troubleshooting is the effort to identify and resolve differences between what was expected and what actually happened. The following four categories narrow the focus of attention and speeds up the evaluation process.

1. Aerodynamic Performance – This applies to any of the five rating parameters of flow, pressure, speed, power and density and how they compare to their respective design quantities.
2. Noise – This applies to any problem in which the ears are the main sensor. Noise and vibration are similar in that they both have amplitude and frequency, but noise is a much lower amplitude and energy content and is measured in dB referenced to Watts. Generally speaking, noise has a much wider frequency range and a higher upper limit than vibration (63Hz to 10 KHz).
3. Vibration – This applies to any problem in which the hands or touching are the main sensor. Amplitude is large when there is a problem. It has much greater energy content with a smaller frequency range (3Hz to perhaps 500 Hz).
4. Premature Failure – Premature Failure applies to anything whose life does not meet that which was expected. The term “failure” does not necessarily mean a catastrophic failure such as when something “blows up”, but a length of time considered as being the useful life of the component.

Troubleshooting must be employed when one of these areas becomes a problem.

Some fan system problems, such as abnormally high operating and maintenance costs and ineffective airflow control, are sufficiently troublesome to justify a system assessment. If the system problems are significant, then a change to the fan, its drive system, or the airflow control devices may be justifiable. Selecting a new, larger fan requires consideration of the same factors that are involved in any initial fan selection. A new fan may be more feasible if the existing one has degraded or requires extensive refurbishment. In high run-time applications, the purchase of a new fan with an energy-efficient motor may provide an attractive payback.

Belt Drive Maintenance Guidelines

Belt tension and alignment should be checked periodically. Proper belt tension is typically the lowest that prevents a belt from slipping at peak load. An important fan maintenance practice to avoid is the use of belt dressing. Belt dressing is a surface treatment that increases the level of friction between a belt and pulley. Because it masks the fundamental cause of slippage, belt dressing only provides a temporary means of reducing noise. Belt slippage should be corrected by either cleaning the drive system or adjusting belt tension.

When installing or replacing belts, ensure they are oriented correctly in accordance with the directions of the manufacturer. Belts are often tagged to show the preferred direction of rotation. Although some belts can be operated in either direction, belt manufacturers often test their belts in one direction and package them with an indication of this direction.

In high-temperature applications, new belts should be operated under low-load conditions and at normal operating temperature for a reasonable period. This run-in time increases the creep strength of the belt.

1. Drives should always be installed with provision for center distance adjustment.
2. If possible centers should not exceed 3 times the sum of the sheave diameters nor be less than the diameter of the large sheave.
3. Be sure that shafts are parallel and sheaves are in proper alignment. Check after first eight hours of operation.
4. Do not drive sheaves on or off shafts. Be sure shaft and keyway are smooth and that bore and key are of correct size.
5. Belts should never be forced or rolled over sheaves. More belts are broken from this cause than from actual failure in service.
6. In general, ideal belt tension is the lowest tension at which the belt will not slip under peak load conditions. Check belt tension frequently during the first 24-48 hours of operation.

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