19
Laboratory Exhaust Systems
®
* Always check motor amps and compare to nameplate rating. Excessive fan speed may overload the motor and
result in motor failure. Do not exceed the maximum cataloged rpm of the fan.
Troubleshooting
Problem
Cause
Corrective Action
Excessive
Noise
Wheel Rubbing Inlet
Adjust wheel and/or inlet cone.
Tighten wheel hub or bearing collars on shaft.
V-Belt Drive
Tighten sheaves on motor and fan shaft. Adjust belt
tension. Align sheaves properly (see procedure).
Replace worn belts or sheaves.
Bearings
Replace defective bearing(s). Lubricate bearings.
Tighten collars and fasteners.
Wheel Unbalance
Clean all dirt off wheel. Check wheel balance.
Low CFM
Fan
Check wheel for correct rotation. Check blade position of
BAP damper, increase fan speed.*
Duct System
Higher pressure than design. Filters need replacement.
High CFM
Fan
Decrease fan speed.
Duct System
Increase BAP damper blade open position. Resize
ductwork. Access door, filters, dampers not installed.
Static Pressure Wrong
Duct system has more
or less restriction than
anticipated
Remove obstructions in system. Use correction factor to
adjust for temperature/altitude. Adjust set point used to
control BAP damper modulation. Resize ductwork. Clean
filters/coils. Change fan speed.*
High Motor Amp Draw
Fan
Check rotation of wheel. Reduce fan speed.
Duct System
Resize ductwork. Check proper operation of isolation and
bypass dampers. Check filters and access doors.
Fan Doesn’t Operate
Electrical Supply
Check fuses/circuit breakers. Check for switches turned off
or disconnected. Check for correct supply voltage.
Drive
Check for broken belts. Tighten loose pulleys.
Motor
Assure motor is correct horsepower and not tripping
overload protector.
Overheated Bearing
Lubrication
Check for excessive or insufficient grease in the bearing.
Mechanical
Replace damaged bearing. Relieve excessive belt tension.
Align bearings. Check for bent shaft.
Excessive Vibration
Belts
Adjust tightness of belts. Replacement belts should be a
matched set.
System Unbalance
Check alignment of shaft, motor and pulleys. Check wheel
balance, rebalance if necessary.
Weak Roof or Support
Structure
Consult Structural Engineer to develop a plan to reinforce
building structure.
System Effect or High
Duct Velocities
Check inlet conditions and duct sizing to ensure duct
velocities are below 1500 fpm and transitions are smooth
and straight with 2-3 wheel diameters of length prior to
entrance to the fan system.
