VENTILATION : AIRFLOW BALANCING
FLEXYII_WSHP-IOM-0909-E Page 50
The actual resistance of ductwork systems is not always identical to 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.
SITE TEST AND MAINTENANCE
Measure the motor absorbed power.
If the absorbed power is greater and the pressure lower than the rated values, the ventilation system has a lower pressure drop
than anticipated. Reduce the flow by reducing the rpm. If the system resistance 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 by increasing the rpm. At the same time you will increase the absorbed power which may result in
having to increase the motor size.
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 13).
Actual diameter (DM) or distance between faces for a given number of
turns from fully closed with SPA belt in (mm)
Pulley
type
Pulley
External
Diameter
Min
Dia /
Min
Dist
Max
Dia /
Max
Dist
Nb of turns
from fully
closed to
fully open
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
95 116 5 114 112 110 108 106 103 101.3 99.2 97.1 95 -
8450 /
D8450
120
20.2 28 5 21 21.8 22.5 23.3 24.1 24.9 25.7 26.4 27.2 28 -
110 131 5 129 127 125 123 121 118 116 114 112 110 -
8550 /
D8550
136
20.6 31.2 5 21.6 22.7 23.8 24.8 25.9 26.9 28 29.1 30.1 31 -
Table_1
The easiest way to determine the fan rotation speed is to
use a Tachometer. If not available the fan rpm can be
estimated using the following two methods.
1
st
Method with the pulley secured in place:
Measure the distance between the two outside faces of the
pulley.
Using table (1) the motor pulley actual diameter can be
estimated.
L
Fig. 13
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