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Model NYB
Pre-Starting Belt Tension Checks
6. Always loosen tension enough to install belts
without stretching, see figure 4.
Belts
Do not force belt(s). Forcing the
belt(s) will break the cords and
Figure 4
cause belt failure
7. For units with two groove pulleys, adjust so the
tension is equal in both belts.
8. 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 5.
Figure 5
9. Belt tension can be adjusted by loosening four
fasteners on the drive frame, see figure 6. This
allows the motor plate to slide on the drive
frame angles for proper positioning.
Fasteners
(4) *Fasteners
*Identical
fasteners on
opposing side
must also be
loosened.
Figure 6
10. Belt tension should be adjusted to allow 1/64
inch (0.397 mm) of deflection per inch of belt
span. For example, a 15 inch (381 mm) belt span
should have 15/64 inch (0.234 mm) (or about
1/4 inch (6 mm)) of deflection with moderate
thumb pressure at mid-point between pulleys, see
figure 7.
Deflection
Slack
Side
Figure 7
4
Models NYD & NYB • Tamper-Resistant Centrifugal Roof Exhaust Fans
13. The adjustable motor pulley is factory set for
the RPM specified. Speed can be increased by
closing or decreased by opening the adjustable
motor pulley. Two groove variable pitch pulleys
must be adjusted an equal number of turns open
or closed.
14. Any increase in speed represents a substantial
increase in the horsepower required by the unit.
15. Motor amperage should always be checked to
avoid serious damage to the motor when speed is
varied.
.
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.
Over tightening will cause excessive bearing wear
and noise. Too little tension will cause slippage at
start-up and uneven wear.
Operation: NYD/NYB
1. Before starting or operating fan, check all
fasteners for tightness. In particular, check
the setscrews in wheel hub (and pulleys, if
applicable).
2. While in the OFF position or before connecting
the fan to power, turn the fan wheel by hand
to be sure it is not striking the venturi or any
obstacle.
3. Start the fan and shut it off immediately to check
rotation of the wheel with directional arrow in the
motor compartment, see figure 3 on page 3.
4. When the fan is started, observe the operation
and check for any unusual noises.
5. With the system in full operation and all
ductwork attached, measure current input to the
motor and compare with the nameplate rating to
determine if the motor is operating under safe
load conditions.
6. Keep inlets and approaches to fan clean and
free from obstruction.
Inspection: NYD/NYB
Inspection of the fan should be conducted at the
first 30 minute and 24 hour intervals of satisfactory
operation.
30 Minute Interval
Inspect bolts, setscrews and motor mounting bolts.
Adjust and tighten as necessary.
24 Hour Interval
Check all internal components. On NYB unit only,
inspect belt alignment and tension. Adjust and
tighten as necessary.
WARNING
IMPORTANT
®
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