Fan Performance Troubleshooting

Published 23 Apr 2020

Portable Fans | ATEX & IECEx Certified | Hazardous Area & Explosive Atmospheres

Article Written By Woodcock & Wilson | 4 of 6 Articles

Woodcock & Wilson are specialist manufacturers of independently certified ATEX fans and IECEx industrial fans for the ventilation of hazardous area locations and potentially explosive atmospheres.

Below is Part 4 in a series of 6 Articles by Woodcock & Wilson discussing fans, the laws, common problems, troubleshooting the main performance issues and getting your fan started again if you encounter any issues.

Fan Performance Troubleshoot

Reasons For Fans Underperforming

Fan running in the wrong direction
Fan running at the wrong speed
Fan incorrectly manufactured
Fan wrongly selected
Fan system problems

Fan Running in the Wrong Direction

While the fan is running up or coasting to a stop, check that the rotation is correct relative to fan type and discharge orientation. Check that the impeller handling is correct for the selected rotation. Examples for centrifugal and axial fans are shown below.

Types of Centrifugal Fan Impellers

Correction Rotation for Axial Flow Impellers

Fan Running at the Wrong Speed

Check the required running speed with the supplier. (Note: If the fan is v belt drive the final running speed may be different from the original selected speed due to the use of standard pulley diameters
Measure actual fan speed with tachometer or other instrumentation
If the fan is operated via an inverter, the fan may be designed to run at specific speed (motor frequency) other than 50 or 60 Hz. If the fan is v belt drive the motor frequency will probably not be the fan speed

Fan Incorrectly Manufactured

This will be unusual but must be considered as part of a fault diagnosis.

Wrong impeller handing in fan case (see above)
Wrong pulleys fitted, giving wrong speed
V belt drive wrongly tensioned causing slip & resulting in wrong speed
Wrong internal clearance between impeller & inlet cone or wrong tip clearance between blades & fan case on an axial fan

Fan Wrongly Selected

Again this will be usual but must be considered as part of a fault diagnosis.

Check that the fan has been selected in accordance with the specification and requirements.

This may include the following:

Selection pressure not referred to the correct section ie -ve on inlet +ve on discharge or a combination of both
Selection pressure not referred to the correct temperature or altitude
Selected fan not taking account of existing or required inlet & discharge duct sizes
Selected fan oversized relative to available space constraints (this may lead to bad inlet & discharge conditions).
Wrong running speed selected ie 50Hz instead of 60hz & vice versa on direct driven fans

System Problems

Fans will only meet the duty point shown on the performance curve under ‘ideal’ installation conditions
Ideal conditions are seldom obtainable in practice consequently there will always be some ‘SYSTEM EFFECT‘

Factors That Influence System Effect

Elbow or bend too close to fan inlet or outlet
Abrupt duct transition
Pre swirl of the incoming air due to duct design (swirl in same direction as rotation
Dampers not fully open
Damper location
Poorly designed fan drives – large drive pulley – solid rather than spoked
Fan inlet box design
Bend orientations at discharge
Free discharge – abrupt expansion
Weather cowls and hoods

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