6
Downblast Centrifugal Roof Exhaust Fans
WARNING
Correct direction of wheel rotation is critical. Reversed
rotation will result in poor air performance, motor
overloading and possible burnout.
WARNING
The fan has been checked for mechanical noises at
the factory prior to shipment. If mechanical noise
should develop, suggested corrective actions are
offered in the Troubleshooting section.
IMPORTANT
Over tightening will cause excessive bearing wear and
noise. Too little tension will cause slippage at startup
and uneven wear.
Model GB
Pre-Starting Belt Tension Checks
8. Always loosen tension enough to install belts
without stretching, see Figure 9.
9. For units with two groove pulleys, adjust so the
tension is equal in both belts.
10. If adjustments are made, it is very important to
check the pulleys for proper alignment. Misaligned
pulleys lead to excessive belt wear vibration, noise
and power loss, see Figure 10.
Figure 10
Wheel Overlap and Gap Dimensions
Figure 7
G
H
Model
G - Overlap
in.
(mm)
H - Gap
in.
(mm)
G
060-095
–
3⁄32
(2)
G
97-163
1/4
(6)
–
GB
071-161
1/4
(6)
–
G
183-243
3/8
(10)
–
GB
180-240
3/8
(10)
–
GB
260-540
1/2
(13)
–
Pre-Starting Checks
1. Check all fasteners and set screws for tightness.
The wheel should rotate freely and be aligned as
shown in Figure 7 below.
2. Wheel position is preset and the unit is test run at
the factory. Movement may occur during shipment
and realignment may be necessary.
3. Only G unit - Centering height alignment can be
accomplished by loosening the set screws in
the wheel and moving the wheel to the desired
position.
4. Only GB unit - Centering can be accomplished by
loosening the bolts holding the drive frame to the
shock mounts and repositioning the drive frame.
5. Only GB unit - Wheel and inlet cone overlap can be
adjusted by loosening the set screws in the wheel
and moving the wheel to the desired position.
6. Only GB unit - Fan RPM should be checked and
verified with a tachometer.
7. Check wheel rotation (viewing from the shaft side)
by momentarily energizing the unit. Rotation should
be clockwise as shown in Figure 8 and correspond
to rotation decal on the unit. If wheel rotation is
incorrect, reverse two of the wiring leads or check
motor wiring for single phase.
Wheel Rotation
Figure 8
Clockwise
Rotation
All Models
Do not force belt(s). Forcing the belt(s)
will break the cords and cause belt failure.
Belts
Figure 9
®
