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Twin City Engineering Supplement ES-191
Fans mounted to or within a structure should be
placed as close as possible to a rigid member such
as a wall or column. The structure must be designed
for rotating equipment; static design for strength is
not sufficient to insure proper operation. Supports for
suspended fans must be cross-braced to prevent side
sway. Structural resonance should be at least 20% from
fan operating speed. Vibration isolators should be used
where applicable.
Any ducting should have independent support; do not
use the fan to support ducting. Isolating the fan from
ductwork with flex connections eliminates transmission
of vibration. Fans handling hot gases require expansion
joints at both the inlet and discharge to prevent
excessive loads caused by thermal growth.
Fan Installation, Factory Assembled Units
Follow proper handling instructions as given earlier.
1. Move the fan to the final mounting position.
2. Remove skid, crates, and packing materials carefully.
3. Place vibration pads or isolation base on mounting
bolts. Line up holes in fan base with bolts.
4. Place fan on mounting structure. Carefully level the
unit using shims as required at all mounting hole
locations. Bolt down the unit.
5. Any grout may now be used. Bolt the fan in position
before applying grout. Do not depend upon grout to
support rotating equipment.
6. Continue with Operations Checklist.
General Motor Maintenance
The three basic rules of motor maintenance are: keep the
motor clean, keep it dry, and keep it properly lubricated.
Blow dust off periodically (with low pressure air) to
prevent the motor from overheating.
Some smaller motors are lubricated for life. Motors
less than 10 hp running about eight hours a day in a
clean environment should be lubricated once every five
years; motors 15 to 50 hp, every 3 years; and motors
50 to 150 hp, yearly. For motors in a dusty or dirty
environment or running 24 hours a day, divide the
service interval by 2. If the environment is very dirty or
high temperatures exist, divide the service interval by
4. Lubrication requirements are normally attached to the
motor. Do not overlubricate.
Drive Maintenance
V-belt drives need periodic inspection and occasional
belt replacement. When inspecting drives, look for dirt
buildup, burrs or obstructions that can cause premature
belt or drive replacement. If burrs are found, use fine
emery cloth or a stone to remove them. Be careful
that dust does not enter the bearings. Check sheaves
for wear. Excessive slippage of belts on sheaves can
cause wear and vibration. Replace worn sheaves with
new ones. Carefully align sheaves to avoid premature
sheave failure.
Inspect the belts for wear. If fraying or other wear
is observed to be mostly on one side of the belts, the
drives may be misaligned. Reinstall the drives according
to the following instructions:
1. Slip (do not pound) the proper sheave onto its
corresponding shaft.
2. Align sheaves with a
straightedge
extended
along the sheaves, just
making contact on the
outside perimeters of both
sheaves. (See Figure 1.)
3. Tighten sheave bolts.
4. Adjust the motor position
to obtain slack. Install
and tighten belts. Use a
matched set of belts. Using
a pry will damage belts.
Never use belt dressing on
any belts.
5. Tighten belts to proper
belt tension. Ideal tension is just enough so that the
belts do not slip under peak load. Recheck sheave
alignment.
6. New belts require a break-in period of operation so
recheck the belt tension after a few days of operation.
7. When replacing belts replace the entire set and follow
the procedure above.
Drive Adjustment
On small fans, the belt tension is adjusted by loosening
the four nuts on top of the motor plate and turning
the four nuts underneath the motor plate to achieve the
proper belt tension. Tighten the top four nuts to hold the
motor plate in place. Care should be taken to maintain
drive alignment as described above. Large fans use a
pivoting motor mounting plate. Adjust the belt tension by
loosening the two nuts and bolts on the pivoting side of
the motor plate, and the nuts that hold the eyebolts to
the motor plate on the other side. Turn the nuts on the
eyebolts that are underneath the motor plate to achieve
the proper belt tension and then tighten the top nuts
and the pivot side nuts and bolts. When tightening the
nuts that are on the eyebolts, take care to maintain
proper drive alignment.
Positioning the motor plate at too high of an angle
may result in the belts rubbing against the belt tube
inside the fan. The motor plate pivot bolt must be
moved up or down to the next hole to keep the drives
centered in the belt tube. The ideal motor plate position
is perpendicular to the belt tube centerline.
Figure 1.
Sheave Alignment
Straightedge
Reversing the sheaves (placing the fan sheave
on the motor shaft) can overspeed the wheel and
cause structural failure.
CAUTION
