Install V-Belts; Tension Measurement Procedure - Carrier 39LA-25 Installation, Start-Up And Service Instructions Manual

Install 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.
Refer to label on inside of fan access door for information on fac-
tory-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 recom-
mended (Table 8).
On current production, the correct tension information is list-
ed on the fan drive label. For older equipment or units with
field-modified drives, use the deflection formula in the fol-
lowing example and the tension data from Table 8.
EXAMPLE:
Given
Belt Span
Belt Cross-Section A, Super Belt
Small Sheave PD
Deflection =
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.
16 in.
5 in.
(Belt Span)
64
16
Deflection =
64

TENSION MEASUREMENT PROCEDURE

1. Measure the belt span (see Fig. 30).
2. Position bottom of the large O-ring on the span scale at the
measured belt span.
3. Set the small O-ring on the deflection force scale to zero.
4. Place the tension checker squarely on one belt at the center of
the belt span. Apply a force on the plunger and perpendicular
to the belt span until the bottom of the large O-ring is even
with the top of the adjacent (next) belt or with the bottom of a
straight edge laid across the outside diameters of the v-belt
sheaves.
5. Remove the tension checker and read the force applied from
the bottom of the small O-ring on the deflection force scale.
6. Compare the force you have applied with the values given in
Table 8. The force should be between the "Used Belt" and
"New Belt" values shown. The maximum value is shown for
"New Belt" and new belts should be tensioned at this value to
allow for expected tension loss. "New Belt" tensions should
be used at initial installation and after job start or 1 to 3 min-
utes of operation. Used belts should be maintained at the
value as indicated in the chart. "Used Belt" tensions should
be used for the 8-hour and subsequent checks. If the belt span
was measured in centimeters, then use the kilograms of force
values for comparison.
NOTE: The ratio of deflection to belt span is 1:64 in either unit of
measurement.
Whenever possible, jog start for a few revolutions or preferably
run drive for approximately 1 to 3 minutes and then re-tension in
accordance with Steps 1-6. Running the drive for a few revolu-
tions or minutes will help seat the belt(s) in the groove(s). This
relatively early re-tensioning may reduce or minimize the amount
of re-tensioning required in the first 24 hours of drive service. Re-
cord information on the label (Fig. 31) found on the door of the
fan section.
30