28
4. With sheaves aligned, tighten cap screws evenly and
progressively.
NOTE: There should be a
1
/
8
-in. to
1
/
4
-in. gap between
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.
Install V-Belts —
When installing or replacing belts, al-
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.
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 (Fig. 50).
6. To determine correct belt tension, use the deflection
formula given below and the tension data from Fig. 50 as
follows:
EXAMPLE:
Given
Belt Span
16 in.
Belt Cross-Section A, Super Belt
Small Sheave Pitch Diameter
5 in.
Solution
1. From Fig. 50 find that deflection force for type A, super
belt with 5-in. small sheave pitch diameter is 4 to 5
1
/
2
lb.
2.
3. Increase or decrease belt tension until force required for
1
/
4
-in. deflection is 5
1
/
2
lb.
Check belt tension at least twice during first operating
day. Readjust as required to maintain belt tension within
the recommended range.
With correct belt tension, belts may slip and squeal
momentarily on start up. This slippage is normal and disap-
pears after unit reaches operating speed.
Excessive belt tension
shortens belt life and may cause bearing and shaft damage.
After run-in, set belt tension at lowest tension at which belts
will not slip during operation.
Deflection =
(Belt Span)
64
Deflection =
16
64
PD —
Pitch Diameter, inches
Fig. 50 — Fan Belt Tension Data
BELT
CROSS
SECTION
SMALL
SHEAVE
PD RANGE
(in.)
DEFLECTION FORCE — LB
Super
Belts
Notch
Belts
Steel Cable
Belts
Min
Max
Min
Max
Min
Max
A
3.0- 3.6
3
4
1
/
4
3
7
/
8
5
1
/
2
3
4
3.8- 4.8
3
1
/
2
5
4
1
/
2
6
1
/
4
3
3
/
4
4
3
/
4
5.0- 7.0
4
5
1
/
2
5
6
7
/
8
4
1
/
4
5
1
/
4
B
3.4- 4.2
4
5
1
/
2
5
3
/
4
8
4
1
/
2
5
1
/
2
4.4- 5.6
5
1
/
8
7
1
/
8
6
1
/
2
9
1
/
8
5
3
/
4
7
1
/
4
5.8- 8.6
6
3
/
8
8
3
/
4
7
3
/
8
10
1
/
8
7
8
3
/
4
C
7.0- 9.4
11
1
/
4
14
3
/
8
13
3
/
4
17
7
/
8
11
1
/
4
14
9.6-16.0
14
1
/
8
18
1
/
2
15
1
/
4
20
1
/
4
14
1
/
4
17
3
/
4
3V
2.65-3.65
3
1
/
2
5
3
7
/
8
5
1
/
2
—
—
4.12-6.90
4
3
/
4
6
7
/
8
5
1
/
4
7
7
/
8
—
—
5V
4.40-6.70
—
—
10
15
—
—
7.1-10.9
10
1
/
2
15
3
/
4
12
7
/
8
18
3
/
4
—
—
11.8-16.0
13
19
1
/
2
15
22
—
—
8V
12.5-17.0
27
40
1
/
2
—
—
—
—
18.0-22.4
30
45
—
—
—
—
a39-1
Fig. 49 — Sheave Alignment
