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Air Handling Unit
Installation, Operation, and Maintenance Manual
April 2021
12.3 Belt Adjustment
Improper belt fitment may cause pulley misalignment,
excessive power consumption, reduced belt life,
premature bearing wear, and noise. To check belt
tension, press the belt firmly at the center of the span
to check deflection objective (Figure 12-4). For quiet
operation, the drive belts should be as loose as possible
without slippage under peak load conditions. If slippage
is occurring, the smaller pulley will appear noticeably
warmer to the touch than the larger pulley. Readjust the
belt tension to achieve uniform pulley temperatures.
Periodically inspect belts for signs of wear, cracking,
stretching, glazing, oil/grease contamination, etc.
Damaged belts must be replaced. If multiple belts are
used, replace all with matched sets.
Do not mix old and new belts.
NOTICE
To replace belts, remove belt guards and loosen motor
hold down bolts. Relieve belt tension by loosening belt
tension adjustment screw on motor base. This will
allow sufficient slack to remove belts with relative ease.
Remove the belts and replace them with new belts of
the same specification. When re-tensioning belts, be
sure to evenly adjust belt tension adjustment bolts to
keep motor shaft parallel with fan shaft.
Following belt installation, slide the motor back to
original position. Tighten the motor hold down bolts.
Use the motor adjustment screws to achieve proper
deflection and re-tighten when deflection requirements
are satisfied. Belts become seated in pulley grooves after
a period of operation, usually within a 24 hour period.
Check belt tension after the first 8 hours of operation
and adjust as necessary. Check at least twice more
during the 24 hour period. To align pulleys, locate the
motor pulley on the motor shaft. Adjust the pulley along
the motor shaft or by moving the entire motor along
the motor mounting bracket. Use a carpenter’s square
to achieve pulley alignment. Rest the shorter leg of the
square along the case of the motor. Use the square’s
longer leg or use a straight edge or string to determine
that the pulleys are aligned and then secure the fixing
bolts.
Figure 12-4.
12.4 Sheave Installation and Alignment
a) Remove the protective coating from the end of
the fan shaft and check that it is free of nicks
and burrs.
b) Check fan and motor shafts for parallel and
angular alignment.
c) Slide sheaves on shafts – do not drive sheaves
on, this may result in bearing damage.
d) Align fan and motor sheaves with a straight-
edge and tighten.
e) Place belts over sheaves. Do not pry or force
belts, this could result in damage to the cords in
the belts.
f) Adjust the tension until the belts appear snug.
Run the fan for a few minutes to allow the belts
to “Set” properly.
g) With the fan off, adjust the belt tension by
moving the motor base. (See section 12.3).
When in operation, the tight side of the belts
should be in a straight line from sheave to
sheave with a slight bow on the slack side.
Figure 12-5.
Figure 12-6.
