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Adjustable--Pitch Pulley on Motor
The motor pulley is an a djustable--pitch type that allows a
servicer to implement changes in the fan wheel speed to
match as--installed ductwork systems. The pulley consists
of a fixed flange side that faces the motor (secured to the
motor shaft) and a movable flange side that can be rotated
around the fixed flange side t hat increase s or re duces the
pitch diameter of this driver pulley. (See Fig. 9.)
C07075
Fig. 9 -- Supply--Fan Pulley Adjust ment
As the pitch diameter is changed by adjusting the position
of the movable flange, the centerline on this pulley shifts
laterally (along the motor shaft). This creates a
requirement for a reali gnment of the pulleys after any
adjustment of the movable flange. Also reset the belt
tension after each realignment.
Check the c ondition of the motor pulley for signs of wear.
Glazing of the belt contact surfaces and erosion on these
surfaces are signs of improper belt tension and/or belt
slippage. Pulley replacement may be necessary.
To change fan speed:
1. Shut off unit power supply.
2. Loosen belt by loosening fan m otor mounting nuts.
(See Fig. 8.)
3. Loosen movable pulley flange setscrew. (See Fig. 9.)
4. Screw movable flange toward fixed flange to increase
speed and away from fixed flange to decrease speed.
Increasing fan speed increases load on motor. Do not
exceed maximum speed specified.
5. Set movable flange at nearest keyway of pulley hub
and tighten setscrew to torque specifications.
To align fan and motor pulleys:
1. Loosen fan pulley setscrews.
2. Slide fan pull ey along fan shaft. Make angular align-
ment by loosening motor from mounting.
3. Tighten fan pulley setscrews and mot or mounting
bolts to torque specifications.
4. Recheck belt te nsion.
Beari ngs
This fan system uses bearings featuring concentric split
locking collars. The collars are tightened through a cap
screw bridging the split portion of the collar. The cap
screw has a Torx T25 socket head. To tighten the locking
collar: Hold the locking collar tightly against the inner
race of the bearing and torque the cap screw to 65--70
in--lb (7.4--7.9 Nm). See Fig. 10.
C08121
Fig. 10 -- Tightening Locking Collar
Motor
When replacing the motor, also replace the external--tooth
lock washer (star washer) under the motor mounting base;
this is part of the motor grounding system. Ensure t he
teeth on the lock washer are in contact with the motor’s
painted base. Tighten motor mounting bolts to 120 +/-- 12
in--lbs.
Changing fan wheel speed by changing pulleys: The
horsepower rating of the belt is primarily dictated by the
pitch diameter of the smaller pulley in the drive system
(typically the motor pulley in t hese uni ts). Do not install a
replacement motor pulley with a smaller pitch diameter
than provided on the original fact ory pulley. Change fan
wheel speed by changing the fan pulley (larger pitch
diameter to reduce wheel speed, smaller pitch diameter to
increase wheel speed) or select a new system (both
pulleys and matching belt(s)).
Before changing pulleys to increase fan wheel speed,
check the fan performance at the target speed and airflow
rate to de termine new motor loading (bhp). Use the fan
performance tables or use the Packaged Rooftop Builder
software program. Confirm that the motor in this unit is
capa ble of operating at the new operating condition. Fan
shaft loading increases dramatically as wheel speed is
increased.
To reduce vibration, replace the mot or’s adjustable pitch
pulley with a fixed pitch pulley (after the final airflow
bala nce adjustment). This will reduce the amount of
vibration generated by the motor/belt--drive system.
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