Aerovent IM-100 - Manual (Page 5)

Aerovent IM-100 5
sheave. Replace belts when they show definite signs
of wear; otherwise the sheaves will become worn to
the point where they also must be replaced. Never put
new belts on a badly worn sheave. This will reduce the
capacity of the drive and cause excessive belt wear.
Most Aerovent fans are provided with an adjusting
screw as a part of the motor base for easy setting of
belt tension. However, small fans or fans using small
horsepower motors may have only a slotted base plate.
When the belt tension is adjusted by moving a motor
on a slotted base, be sure to block the motor tightly
and squarely before tightening the hold-down bolts,
keeping the motor sheave in line with the belt. The
motor sheave must be parallel to and in line with the
fan sheave.
When you make replacement of belts on a multi-
groove drive, be sure they are used in a matched set.
If you are not sure the belts are matched, observe them
in operation. The tight side should be perfectly straight
and the belts should run smoothly and in line. The slack
side should bow out and also be in line. If one of the
belts extends out considerably farther than another, it is
an indication that the belts are not matched and should
be changed. If there is only a slight difference, the nor-
mal stretching in the first hours of operation will equalize
the belt lengths and the belts will be well matched.
Adjusting Variable Pitch
Sheaves
Many Aerovent belt driven fans are furnished with
variable-pitch motor sheaves. Sheaves may be adjusted
for lower fan speeds without concern of overloading
motors. When adjusting sheaves to increase the fan
speed, check the motor current to be sure the motor
is not overloaded. Keep the motor current within the
nameplate and service factor ratings.
The sheaves used are easily adjusted. They come in
various styles, depending upon the size drive and motor
shaft. They are all fitted with hollow head knurled point
safety set screws.
The following steps should be taken to adjust the
pitch diameter.
1. Release belt tension and remove the belt or belts
from the sheave.
2. Loosen the set screw and remove the key hold-
ing the adjustable half of the groove (keys used on
styles 2, 3, 5 and 6 only). With styles 3 and 6, it
may be necessary to remove the sheave from the
shaft to remove the key.
3. Rotate the adjustable half of the sheave out for a
smaller pitch diameter (decreased speed) or in for a
larger pitch diameter (increased speed). Each one-
half turn will change the pitch diameter one-tenth
of an inch. Adjust two-groove sheaves the same
amount on each groove. 4L or A belts will oper-
ate satisfactorily with the sheave fully closed to a
maximum of five full turns open. 5L or B belts will
operate satisfactorily with the sheave one full turn
open to a maximum of six full turns open. (This will
insure full contact of the sheave in the groove.)
4. Replace the key and tighten the set screw to lock
the sheave half in position.
5. Replace the belts and tighten to the proper tension.
If an extreme amount of adjustment has been made,
it may be necessary to replace belts with another
length.
V-Belt Drive Alignment
Proper alignment and balance of the V-belt is as impor-
tant as a well-balanced propeller. To insure smooth fan
operation, the following should be checked:
1. The fan and motor sheaves must be in axial align-
ment. Shafts are parallel in both the vertical and
horizontal planes (Figure 3).
Figure 3. Fan and Motor Sheave Axial Alignment
2. The fan motor sheave must be in radial align-
ment. When sheaves are of equal width, align with
a straightedge (Figure 4a). When sheaves are of
unequal width, align the center of the sheaves (Figure
4b).
Figure 4. Sheave Alignment
Type 4 Type 5 Type 6
Finished Bore Finished Bore Bushing Type
S.S. in Keyway Key Type With Key
Type 1 Type 2 Type 3
Finished Bore Finished Bore Bushing Type
S.S. on Flat Key Type With Key
Drive
Fan
Motor
Drive
Fan
Motor
Top View
(Horizontal Alignment)
Side View
(Vertical Alignment)
Figure 2. Types of Sheaves
Straightedge Touching Sheaves
At Arrows
4a 4b