Page 10
TMC-647-(Rev E) - 01/06
MOORE FANS LLC, Marceline, MO 64658 Phone (660 ) 376-3575 FAX (660) 376-2909
3.2 ANNUAL INSPECTION
3.3 VIBRATION AND UNBALANCE
3.3.2 FAN UNBALANCE
Vibration is most likely to be caused by the fan if the blades
are not set at the same angle. If the blades are properly set, the
fan is the least likely cause of vibration. All fan components
are balanced to within ±0.2 ft-lbs.
3.3.1 GENERAL
No piece of rotating equipment is perfectly balanced. It
is always possible that the minute unbalances of the various
components may combine to provide a noticeable lack of
balance. This rarely occurs, since it is unlikely that all unbal-
anced components will become assembled with their heavy
sides in the same direction. Nevertheless, if unbalance is
noted, the various components should be rotated into differ-
ent positions to see if this might cure the unbalanced condi-
tion.
If vibration or unbalance occur, either at the time of
installation or later during the operation of the unit, its cause
may be determined by following the directions below.
3.2.3 CLOSE INSPECTION
The yearly inspection should be a very thorough one.
A11 nuts and bolts should be checked and careful scrutiny
given to all highly stressed areas.
Inspect the resilient mounts as follows: With the fan
turned off, grasp each blade and feel for looseness at the
mount. If in doubt, the blade should be removed and the
mount assembly visually inspected. Wear is indicated by a
fretting effect and the resilient mount material will show
signs of extruding from the cavity. If these indications are not
apparent, replace the blade and continue normal operations.
Inspect the blade tips for any signs of cracking and the
fan ring for any scoring that might indicate that the blades
have been striking or rubbing against the fan ring.
3.2.2 CHECK SYSTEM PRESSURE
Radiator sections may be effected by the accumulation
of dust and dirt in some atmospheres. (Cottonwood seeds
are particularly troubling.) In cooling towers, it is not un-
common for scale and foreign matter to build up on the decks
and eliminator sections. These accumulations may signifi-
cantly increase the static pressure. Adjust the blade angle if
necessary as described in Section 4.4 Checking Blade Load.
3.2.1 CLEAN BLADES IF INDICATED
A smooth blade surface is essential for efficient fan
performance. If an incrustation forms on the blades it should
be removed. Use steel wool as an abrasive along with a mild
detergent or a very mild form of solvent. Lye must not be
used because it attacks aluminum readily.
3.1.8 CHECK THE ROTARY UNION
Check to be sure that adequate slack is present in the
pneumatic hose(s) to allow a few degrees tilt of the rotary
union to prevent damage to the internal bearings.
Rotary union bearings are sealed and require no lubrica-
tion. If oil misting is not provided in the line, leakage at the
seal may develop over time. This may be prevented by
lubricating with a few drops of SAE30 oil.
3.1.7 HUB INSPECTION
If damage to the fan has occurred, the hub should be
carefully inspected since subtle damage may have been
caused that is not readily apparent. Check the hub for any
sign of bending or twisting of the hub tubes. If the unit has
an automatic hub, resilient members are furnished within
the hub tubes. With the air off, grasp the end of each clevis
and try to twist it. If it is not extremely difficult to twist the
tube, the resilient member has failed.
Hub tubes cannot be replaced in the field on manual
fans and a new hub should be ordered. Hub tubes can be
replaced in the field on automatic fans.
Bushings are frequently cracked during a fan wreck and
should be carefully inspected. Damage may occur to the
stainless steel studs that attach the hub to the bushing. It is a
good idea to replace the studs when replacing a damaged fan
blade.
For automatic hubs, the actuator diaphragm should be
inspected for any signs of crazing or cracking indicating that
the diaphragm should be replaced. Operation in high-tem-
perature applications will accelerate aging. It is also possible
that, if the diaphragm is fully inflated and there is no pressure
relief, a sudden, extreme temperature rise may rupture the
diaphragm.
If the fan is in an unbalanced condition, the frequency of
vibration of the structure will be that of the RPM of the fan
and is quite low. In the case of large fans, the frequency is
often low enough to be mentally counted along with the
rotation of the fan. A vibration of 500 CPM or less will be
felt as a weave in the structure rather than a vibration.
Below 400 CPM, the vibration may be mentally counted
and above that point may be read with a frequency meter.
Before assuming fan unbalance, check for loose bearing
seats or bearings journaling the shaft on which the fan is
mounted. This condition will cause the shaft to rotate
eccentrically. After all checks have been made and the fan
is still determined to be unbalanced, field balancing may be
accomplished as described in Section 3.3.7.
It should be noted that the loads imposed on the drive
shaft and its supporting bearings by fan unbalance are
negligible. A rotating centrifugal load of 100 pounds, due to
unbalance, would be extremely objectionable and possibly
even damage the structure on which the drive was mounted.
By contrast, it would be unlikely that the drive shaft of a fan,
As with any industrial equipment, before entry into fan chamber, strict adherence to ALL Lock-
out / Tag-out procedures is well advised!
MAINTENANCE
To Next Page
Loading...