5 - 5 . 1 . If a slight bow in the belts is evi-
dent as shown in Figure 5-1, the belts are
usually adjusted satisfactorily. However,
a more accurate method of checking belt
tension is by the spring scale measurement
that follows. Measure the belt span (t) as
shown in Figure 5-2. At the center of the
span (t) apply a force perpendicular to the
span by attaching a spring scale to the two
outside belts. The force applied to the
spring scale should be sufficient to deflect
ing Belt Tension
the belts 1/64" for every inch of span length
(t). For example: The deflection of a 100"
span would be 100/64" or 1-9/16", thus, the force applied to the spring scale should deflect
the belts to 1-9/16". When the belts are deflected the necessary distance, compare the spring
scale reading (in lbs. force) with the values given in Table 5-4. If the reading is between the
value for normal tension and 150% normal tension, the belt tension should be satisfactory. A
reading below the value for normal tension indicates the belt slack should be reduced, and,
conversely, a reading exceeding the value for 150% normal tension indicates the belt slack
should be increased. Experience has shown that a new drive belt can be tightened initially to
two times normal tension to allow for any drop in tension during run in.
TABLE 5-4. BELT TENSION
5-5.2. When installing new belts, do not
pry the belts over the pulley grooves. Loos -
en the anchor nuts and the belt tightener
shown in Figure 5-3 and push the motor
toward the compressor. After the belts are
over the pulleys, use the belt tightener to
adjust the belt tension.
Checking Belt Tension
5-3
