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Table 21: Belt Deflection Force (not applicable for Exhaust Fans - see “Belts” on page 74)
Mounting and Adjusting Motor Sheaves
Figure 88. VM and VP variable pitch sheaves
VM and VP Variable Pitch Sheaves
Mounting:
1. All sheaves should be mounted on the motor shaft with
setscrew "A" toward the motor (see Figure 88 on
page 82).
2. Be sure both the driving and driven sheaves are in align-
ment and that the shafts are parallel.
3. Fit internal key "D" between sheave and shaft, and lock
setscrew "A" securely in place.
Adjusting:
1. Slack off all belt tension by moving the motor toward the
driven shaft until the belts are free from the grooves. For
easiest adjustment, remove the belts.
2. Loosen setscrews "B" and "C" in the moving parts of the
sheave and pull out external key "E" (see Figure 88). This
key projects a small amount to provide a grip for removing.
3. Adjust the sheave pitch diameter for the desired fan speed
by opening the moving parts by half or full turns from
closed position. Do not open more than five full turns
for "A" belts or six full turns for "B" belts.
Adjust both halves of two-groove sheaves by the same
number of turns from closed to ensure that both grooves
have the same pitch diameter.
4. Replace external key "E" and securely tighten setscrews
"B" over the key. Tighten setscrews "C" into the keyway
in the fixed half of the sheave.
5. Put on belts and adjust the belt tension. Do not force belts
over grooves. Loosen the belts by adjusting the motor
base closer to the fan shaft.
CROSS SECTION
SHEAVE DIAMETER (INCHES) DEFELCTION FORCE (LBS.)
SMALLEST SHEAVE
DIAMETER RANGE
RPM RANGE
BELT DEFLECTION FORCE
CROSS SECTION A, B, 5V CROSS SECTION AX, BX, 5VX
USED BELT NEW BELT USED BELT NEW BELT
A, AX
3.0-3.6
1000-2500 3.7 5.5 4.1 6.1
2501-4000 2.8 4.2 3.4 5.0
3.8-4.8
1000-2500 4.5 6.8 5.0 7.4
2501-4000 3.8 5.7 4.3 6.4
5.0-7.0
1000-2500 5.4 8.0 5.7 9.4
2501-4000 4.7 7.0 5.1 7.6
B, BX
3.4-4.2
850-2500 4.9 7.2
2501-4000 4.2 6.2
4.4-5.6
860-2500 5.3 7.9 7.1 10.5
2501-4000 4.5 6.7 7.1 9.1
5.8-8.6
860-2500 6.3 9.4 8.5 12.6
2501-4000 6.0 8.9 7.3 10.9
5V, 5VX
4.4-6.7
500-1749 10.2 15.2
1750-3000 8.8 13.2
3001-4000 5.6 8.5
7.1-10.9
500-1740 12.7 18.9 14.8 22.1
1741-3000 11.2 16.7 13.7 20.1
11.8-16.0
500-1740 15.5 23.4 17.1 25.5
1741-3000 14.6 21.8 16.8 25.0
T w o G r o o v e
C
A
B
B
D
E
C
A
D
E
D
C
S i n g l e G r o o v e
K e y " E " p r o j e c t s
t o p r o v i d e a g r i p
f o r r e m o v a l .
D o n o t o p e r a t e
s h e e v e s w i t h f l a n g e
p r o j e c t i n g b e y o n d
t h e h u b e n d .
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