IOM / ROOF-TOP FLEXY™ Series - Page 11
AIR FLOW BALANCINGAIR FLOW BALANCING
AIR FLOW BALANCINGAIR FLOW BALANCING
AIR FLOW BALANCING
The actual resistance of ductwork systems is not always
the same as the calculated theoretical values. To rectify
this, it may be necessary to modify the pulley and belt
setting. To this effect, the motors are fitted with variable
pulleys.
TEST
You should already have measured the + ve pressure
experienced on fan discharge, as well as the pressure
experienced in the return duct to the fan.
Measure the motor absorbed power.
If the absorbed power is greater and the pressure lower
than the rated values, your system has a lower pressure
drop than anticipated. Reduce the flow. If the system
resistence is significantly lower than design, there is a
risk that the motor will overheat resulting in an
emergency cut out.
If the absorbed power is lower and the pressure greater
than the rated values, your system has a higher
pressure drop than anticipated. Increase the flow. At
the same time you will increase the absorbed power
which may result in having to fit a larger motor.
To carry out the adjustment and to avoid a time-
consuming re-start, stop the machine and if necessary
lock the main switch.
First unscrew the 4 Allen screw(s) on the pulley (see
Figure 11).
Slacken the belts, then remove then (see § "BELT
TENSION").
Figure 12
The flow can now be increased by turning the flange(s)
to move them closer (or alternatively, move them apart
to reduce the flow).
For two-groove pulleys, turn the flanges the same
number of turns.
If necessary, check the pulley diameter by measuring
the outer diameter of a belt positioned in the groove
(Figure 12).
Finally, replace and tension the belts before carrying
out a test. Re-check the absorbed power levels. Repeat
the operation until a satisfactory result has been
achieved.
To minimise the number of operations, refer to the flow
/ pressure charts on the following pages for the type of
fans used. With reference to the following example,
you can estimate your flow and thus calculate the
necessary adjustment.
ALLEN wrench 4
Figure 11
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