SERVICING
37
4. For gas heat units, the airflow must be adjusted so that
the air temperature rise falls within the ranges given stated
on Data Plate by adjusting the variable pitch sheave on
the motor (see Blower Performance section in appropriate
Spec Sheet Manual for correct pulley adjustment).
5. Take motor amperage draw to determine that the motor
is not overloaded during adjustments.
RISE = SUPPLY -
T T
T
T
SUPPLY
RETURN
CHECKING TEMPERATURE RISE
S-205 CHECKING BELT TENSION
NOTE: Section on high static tables may require a field motor
change.
BELT DRIVE MODELS ONLY
TENSION AND A LIGNMENT A DJUSTMENT
Check drive for adequate run-in belt tension. Correct belt
tension is very important. A belt that is loose will have a
substantially shorter life, and a belt that is too tight may
cause premature motor and bearing failure. Correct belt
tension on these units can be checked by measuring the
force required to deflect the belt 1/8" at the midpoint of the
span length (See DRIVE BELT TENSION ADJUSTMENT
Figure). Belt tension force can be measured using a belt
tension gauge, available through most belt manufacturers.
The correct deflection force is 5 Ibs. for a new belt and 3.5 Ibs.
for a belt that has been run in. New belt tension includes
initial belt stretch.
When new V-belts are installed on a drive, the initial tension
will drop rapidly during the first few hours. Check tension
frequently during the first 24 hours of operation. Subsequent
retensioning should fall between the minimum and maximum
force. To determine the deflection distance from the normal
position, use a straightedge or stretch a cord from sheave to
sheave to use as a reference line. On multiple belt drives, an
adjacent undeflected belt can be used as a reference.
*Apply force to the center of the span.
t = Span length, inches
C = Center distance, inches
D = Larger sheave diameter, inches
d = Smaller sheave diameter, inches
h = Deflection height, inches
DRIVE BELT TENSION ADJUSTMENT
7.5 - 12.5 TON MODELS
BELT DRIVE Used New
7.5 Ton 2.6 to 3.6 3.75 +/- 0.5 4.0 +/- 0.5 9/32 +/- 1/16
8.5 Ton 2.6 to 3.6 3.75 +/- 0.5 4.0 +/- 0.5 9/32 +/- 1/16
10 Ton 3.0 to 4.0 3.75 +/- 0.5 4.0 +/- 0.5 9/32 +/- 1/16
12.5 Ton 2.6 to 3.6 3.7 5 +/- 0.5 4.0 +/- 0.5 9/32 +/- 1/16
A, A X Stand ar d
MODEL
DEFLECTION
(in)
DEFLECTION
FORCE (lbs)
SHEAVE
DIAMETE
R (in )
TYPE
RECOMMENDED POUNDS OF FORCE PER BELT
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