Fig. 4
If adjustments are made, it is very important to check the pulleys for proper alignment. Misaligned pulleys lead to excessive
belt wear, vibration, noise and power loss. (See Fig. 5)
For all BDF units, belt tension can be adjusted by loosening four fasteners (marked “R”) on the drive frame. The motor plate
slides on the slotted adjusting arms (see Fig. 6). Belt tension should be adjusted to allow 1/64” of deflection per inch of belt
span. For example, a 15” belt span should have 15/64” (or about 1/4”) of deflection with moderate thumb pressure at mid-
point between pulleys (See Fig. 7). Over tightening will cause excessive bearing wear and noise. Too little tension will cause
slippage at startup and uneven wear.
The adjustable motor pulley is factory set for the RPM specified. Speed can be increased by closing or decreased by opening
the adjustable motor sheave. Two groove variable pitch pulleys must be adjusted an equal number of turns open or closed.
Any increase in speed represents a substantial increase in the horsepower required by a unit. Motor amperage should always
be checked to avoid serious damage to the motor when speed is varied.
CORRECT
WRONG
WRONG
WRONG
Fig. 5
R
Belt Span
Deflection =
Belt Span
64
NOTE:
Identical fasteners on
opposing side must
also be loosened.
Fig. 6
Fig. 7
2
PRE-STARTING CHECKS
Check all fasteners for tightness. The wheel should rotate freely and not rub on the inlet venturi’s. Turn the fan on momentarily
to check for unusual vibration or noise. Do not run the fan more than a few seconds without being connected to the system
for which it was designed. Motor overloading and burnout may result from lack of system static pressure.
Also check direction of wheel rotation. Improper rotation will result in reduced airflow and pressure capabilities. Rotation is
always in the same direction as airflow at the outlet. See housing and wheel examples in Figure 4.
AIRFLOW
R
O
T A
T O
I
N
AIRFLOW
R
O
T A
T O
I
N
