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Fig. 22 — Sheave Alignment
4. With sheaves aligned, tighten cap screws evenly and
progressively.
NOTE: There should be a
the mating 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 wob-
ble. Check by rotating sheaves and rechecking sheave
alignment. When substituting field-supplied sheaves for
factory-supplied sheaves, consider that the fan shaft
sheave has been factory balanced with fan and shaft as an
Fig. 21 — Determining Sheave-Shaft Overhang
1
/
-in. to
1
/
-in. gap between
8
4
assembly. For this reason, substitution of motor sheave is
preferable for final speed adjustment.
Install V-Belts —
ways use a complete set of new belts. Mixing old and new belts
will result in the premature wear or breakage of the newer
belts.
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 maximum deflection force
recommended (Table 5).
On current production, the correct tension information is
listed on the fan drive label. For older equipment or units
with field-modified drives, use the deflection formula in
the following example and the tension data from Table 5.
EXAMPLE:
Given
Belt Span
Belt Cross-Section A, Super Belt
Small Sheave PD
Solution
a. From Table 5 find that deflection force for a new
type A, super belt with 5-in. small sheave PD is
8 lb.
b.
17
When installing or replacing belts, al-
16 in.
5 in.
(Belt Span)
Deflection =
64
16
Deflection =
64
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