7
IMH IO&M
B51221-002
Changing Shaft Speed
All belt driven ventilators (5HP or less) are equipped with
variable pitch pulleys. To change fan speed, perform the
following:
1.
Loosen setscrew on driver (motor) pulley and
remove key, if equipped.
2.
Turn the pulley rim to open or close the groove
facing. If the pulley has multiple grooves, all must
be adjusted to the same width.
3. After adjustment, inspect for proper belt tension.
Speed Reduction
Open the pulley in order that the belt rides deeper in the
groove (smaller pitch diameter).
Speed Increase
Close the pulley in order that the belt rides higher in the
groove (larger pitch diameter). Ensure that the RPM lim
-
its of the fan and the horsepower limits of the motor are
maintained.
Replacing Fan Pulleys and Belts
1. Remove pulleys from their respective shafts.
2. Clean the motor and fan shafts.
3. Clean bores of pulleys and coat the bores with heavy oil.
4. Remove grease, rust, or burrs from the pulleys and shafts.
5. Remove burrs from shaft by sanding.
6. Place fan pulley on fan shaft and motor pulley on its shaft.
Damage to the pulleys can occur when excessive force
is used in placing the pulleys on their respective shafts.
7. Tighten in place.
8.
Install belts on pulleys and align as described in the
Belt
and Pulley Installation
section.
RPM Derating Factor
Steel
Temp.°F
RPM
70
1.00
200
.98
300
.96
400
.94
500
.91
600
.87
700
.81
800
.75
Aluminum
Temp.°F
RPM
70
1.00
200
.93
300
.79
For elevated airstream temperatures, the maximum RPM limits must
be derated by the factors found in the tables above.
Bearing Replacement
The fan bearings are pillow block ball bearings. Bearings
should be replaced individually from each side of fan.
An emery cloth or file may be needed to remove imper
-
fections in the shaft left by the setscrews.
1.
Mark the position on the shaft of both bearing races, set-
screws, and the wheel and pulley. Note the clearance be
-
tween the wheel and inlet.
2. Remove the fan pullet and belts.
3.
Remove the inlet side panel by removing the bolts around
the perimeter of panel.
4.
Remove inlet cone by removing attaching bolts/nuts
around perimeter of the inlet plate.
5. Remove wheel from the shaft. A 2-jaw puller may be
needed.
6. Remove bearing hold-down bolts. Remove shaft and
bearings as one unit.
7.
Remove anti-corrosion coating from the shaft with a suit-
able degreaser.
8. Remove the bearing from the shaft using a bearing puller.
If a bearing puller is not available, tap on the bearing with
a wood block and hammer to remove it.
9. Smooth and clean the shaft and bearing bore thoroughly.
10.
Place the bearings into position making sure they are not
on a worn section of the shaft. Tapping the inner ring face
with a soft driver may be required.
Do not hammer on the housing.
11.
The outer ring of the bearing is spherical and swivels
in the housing to compensate for misalignment. Secure
hold-down bolts, but do not fully tighten.
12.
Align the setscrews on the bearings and tighten one set-
screw on each bearing.
13. Rotate the shaft to allow the bearing outer rings to find
their center of free movement.
14.
Install the wheel on the shaft and install the inlet side pan-
el in its original location. Adjust bearing position and inlet
side panel to center the wheel in the inlet.
15. Tighten bearing hold-down bolts to proper torque. Refer
to
Torque Chart.
16. Turn the shaft by hand. Resistance should be the same as
it was before hold-down bolts were fully tightened.
17. Tighten bearing setscrews to specified torque as noted in
the
Torque Chart
.
18. Reinstall the pulley and adjust the belt tension. Refer to
Belt and Pulley Installation
.
19. Test run the fan and trim balance as necessary (.0785 in/
sec max.).
20. Re-tighten setscrews on bearings, sheave, and wheel.
Recheck belt tension and adjust as needed.
Troubleshooting
Problem and Potential Cause
Low Capacity or Pressure:
•
Incorrect direction of rotation. Make sure the fan rotates
in same direction as the arrows on the motor or belt
drive assembly.
•
Poor fan inlet conditions. There should be a straight
clear duct at the inlet.
•
Improper propeller alignment.
Excessive Vibration and Noise:
•
Damaged or unbalanced propeller.
•
Belts too loose; worn or oily belts.
•
Speed too high.
•
Incorrect direction of rotation. Make sure the fan rotates
in same direction as the arrows on the motor or belt
drive assembly.
•
Bearings need lubrication or replacement.
•
Fan surge or inlet or outlet conditions.
Overheated Motor:
•
Motor improperly wired.
•
Incorrect direction of rotation. Make sure the fan rotates
in same direction as the arrows on the motor or belt
drive assembly.
•
Cooling air diverted or blocked.
•
Improper inlet clearance.
•
Incorrect fan RPMs.
•
Incorrect voltage.
Overheated Bearings:
• Improper bearing lubrication
•
Excessive belt tension.
