10
Supreme Exhaust Fan Service
DRIVE MOTOR AND DRIVEN BLOWER WHEEL PULLEY VARIATIONS:
Drive Pulley
This pulley is a variable pitch pulley. The pitch diameter of the pulley is adjustable to allow speeding up or slowing down of
the blower wheel a small amount within the adjustment range of the pulley. For small single groove pulleys, an allen head
set screw is provided in the shoulder on the bottom side of the pulley, to tighten the pulley to a flat spot on the shaft of the
motor. On the top side of the pulley, an allen head set screw is provided in the shoulder to tighten the threaded adjustable
portion of the pulley to a flat spot on the threaded hub of the pulley.
On pulleys of a larger size, the flat spots on both the motor shaft and the threaded hub of the pulley, are replaced with key-
ways and square or rectangular keys. The key slides into the keyway of the motor shaft and pulley keyway and the shoul-
der set screw locks the pulley into place. After the threaded adjustable portion of the pulley has been adjusted to the proper
setting, align the keyway and slide the second key into the keyway. Tighten the set screw to lock the pulley at this setting.
The two groove variable pitch pulleys are similar to above, except that the set screw that locks the pulley to the motor
shaft, is located inside between the grooves. The threaded groove adjustment must be opened to allow access to this set
screw. There are two set screws, one on each outside hub, that locks the outside of each groove to the key at the proper
adjustment setting. Caution must be exercised to make sure that each of the two grooves are adjusted to the same setting
to maintain equal tension on both belts.
Driven Pulley
The driven pulley is a fixed size (not adjustable). It is secured to the blower shaft with a split tapered bushing and cap
screws. To install the pulley and bushing to the blower shaft, slip the pulley and bushing onto the shaft. Align the clearance
holes in the bushing flange with the threaded holes in the pulley hub. Insert the cap screws through the clearance holes of
the bushing flange and screw the cap screws loosely into the threaded holes of the pulley hub. Position the assembly on
the shaft (see “Pulley Alignment”) and tighten the cap screws progressively and uniformly until tight. To remove the pulley,
remove the cap screws. Screw the cap screws into the threaded holes in the bushing flange. Progressively tighten the cap
screws against the pulley hub until the bushing breaks free from the pulley. Remove the bushing and pulley from the shaft.
Remove the cap screws form the threaded holes in the bushing flange.
The two groove driven pulleys are identical to the single groove pulleys for installation and removal.
Pulley Alignment
For access to the motor, pulleys, belts and fan bearings, loosen the wing nuts on the sides of the drive assembly cover and
hinge cover up. Install the motor cover support arm for safety to ensure that the motor cover will not drop while working on
the drive assembly.
The pulley alignment should be accomplished by laying a level or straight edge across the pulleys. Both pulleys should be
level and aligned. If not perfectly level, remove the belt (see “How To Replace Belt”), loosen the driven pulley (See “Driven
Pulley”), and adjust up or down to obtain level. Firmly re-tighten the pulley and reinstall and re-adjust the belt. If the pulleys
are not properly aligned, excessive belt wear will occur. It may cause fan vibration and could cause the belt to “jump” off
the pulleys.
To Adjust Belt Tension
The bottom tension bolt is welded to the motor frame plate, the top tension bolt is loose. To increase the belt tension, turn
the lock nuts counter-clockwise at the motor mounting plate on the side towards the motor until substantially loose.
Gradually tighten both lock nuts clockwise at the motor mounting plate on side away from motor until the belt is properly
tensioned. Proper belt tension is when the belt deflects about one inch at the center when squeezed firmly from both sides.
Firmly re-tighten the lock nuts on the motor side of the motor mounting plate. To decrease the belt tension, reverse the
above procedure.
To Replace Belt
Turn lock nuts on belt tension bolts clockwise at motor mounting plate on side away from motor way down to allow the
motor mounting plate to swing in and allow slack on the belt. Remove the old belt and install the new belt. See “How To
Adjust Belt Tension” to tighten new belt.
To Next Page
Loading...