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replaced with fixed pitch sheaves by the air balancer prior to
the final system air balance.
Do not exceed maximum fan speed rpm with adjustable
sheave. Equipment damage may result.
3.
Rotate each sheave one-half revolution to determine whether
the sheave is wobbly or the drive shaft is bent. Correct any
misalignment.
4.
With sheaves aligned, tighten cap screws evenly and
progressively.
NOTE: There should be a
/
1
8
part hub and the bushing flange. If gap is closed, the bushing is
probably the wrong size.
5.
With taper-lock bushed hubs, be sure the bushing bolts are
tightened evenly to prevent side-to-side pulley wobble.
Check by rotating sheaves and rechecking sheave alignment.
When substituting field-supplied sheaves for factory-supplied
sheaves, consider that fan shaft sheave has been factory bal-
anced with fan and shaft as an assembly. For this reason, sub-
stitution of motor sheave is preferable for final speed
adjustment.
Fig. 55 — Determining Sheave-Shaft Alignment
CAUTION
-in. to
/
-in. gap between the mating
1
4
A39-137tf
V-Belts
When installing or replacing belts, always use a complete set of
new belts. Mixing old and new belts will result in the premature
wear or breakage of the newer belts. See Fig. 56.
Refer to label on inside of fan access door for information on
factory-supplied drive.
1.
Always adjust the motor position so that V-belts can be
installed without stretching over grooves. Forcing belts can
result in uneven stretching and a mismatched set of belts.
2.
Do not allow belt to bottom out in sheave.
3.
Tighten belts by turning motor-adjusting jackscrews. Turn
each jackscrew an equal number of turns.
4.
Equalize belt slack so that it is on the same side of belt for all
belts. Failure to do so may result in uneven belt stretching.
5.
Tension new drives at the deflection force recommended
(Table 32).
On current production, the correct tension information is listed on
the fan drive label. For older equipment or for units with field-
modified drives, use the deflection formula given in the following
example and the tension data from Table 32.
SMALL
DEFLECTION
"O" RING
FORCE
(LB.)
STRAIGHT
EDGE
SPAN SCALE
LARGE "O" RING
V-BELT
Fig. 56 — Fan Belt Tension
118
BELT
SPAN
ADJACENT
V-BELT
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