MOORE FANS LLC, Marceline, MO 64658 Phone (660 ) 376-3575 FAX (660) 376-2909 Page 9
TMC-647-(Rev E) - 01/06
3.0 MAINTENANCE
3.1.5 OPERATION BY VARIABLE SPEED MOTORS
Moore fans are ideal for use with variable speed mo-
tors. The resilient blade mounting, unique with these fans,
eliminates resonant frequencies. There are no critical speeds
to be avoided. There is, however, a minimum RPM below
which there is not enough centrifugal force to lift the blades
enough to prevent their repeatedly striking the clevis dur-
ing operation. This is a cause of damaging clevis wear in
addition to the causes discussed in the preceding para-
graph.
The minimum RPM should be no less than 10% of full
RPM or the minimum recommended by the motor or drive
manufacturer, whichever is greater. The fan should be shut
off rather than reducing the motor speed beyond this point.
3.1.1 PURPOSE
Fan failure is most likely the result of destructive repeti-
tive stress acting over a period of time. These stresses may be
caused by mechanical abuse, e.g. rough gears or drive shaft
imbalance, or by aerodynamic abuse such as blade overload
or abnormal flow conditions. Fortunately, these stresses
manifest themselves in typical ways that may easily be
detected on inspection if one knows what to look for. The
purpose of this section of this manual is to describe the
symptoms of potentially damaging mechanical problems
and how they can be corrected. Aerodynamic abuses are
covered in Section 4.0 Operation.
3.1.2 FREQUENCY OF INSPECTION
The frequency of inspection varies widely in accordance
with the severity of service and a suitable inspection sched-
ule should be developed with experience over time. During
the first week of operation, at least one inspection should be
made. At these initial inspections, in addition to the items
listed below, check all nuts for tightness to make certain that
all were tightened properly at installation (but do not re-
torque already tightened nuts). Following the first week, it
is probable that inspections of the fan need be made no more
frequently than inspection of the drive.
3.1.3 CHECK BLADE DROOP AND ANGLE
Turn off the unit and watch the blade tips. A looseness of
the clamp nut will permit a blade to flatten in angle. This
usually can be detected by looking at the tips of the blades
while the fan is slowing down. At the same time, before the
unit comes to a complete stop, watch the track of the blade
tips to see that all blades have the same droop. If one or more
blades have a substantially different droop than the other
blades, or if all of the blades show a greater droop than at the
last inspection, investigate further. Excessive droop has two
possible causes:
1. A damaged resilient mount that requires replacement
2. Wear at the end of the box section against the clevis,
indicating that the box section has been riding against the
clevis during operation. This type of wear indicates that the
blade is not rising during operation a sufficient distance to
clear the stop. If only one blade is affected, that blade is set at
a steeper angle than the other blades. This should be checked
and corrected.
3.1.4 CHECK FOR WEAR ON CLEVISES
Clevises should be examined at each inspection for
possible wear against the end of the box section. Since contact
between the box section and the face of the clevis provides a
stop to prevent excessive droop when the fan is shut down,
there will undoubtedly be a mark on the face of the clevis at
the point of contact. There should, however, be no evidence
of wear which would indicate repetitive contact between the
two parts during operation. If wear at this point is indicated,
a check should be made of blade loading as set out under
Section 4.4 Checking Blade Load. If blade overload is not
responsible, the end of the box section can be dressed off with
a file to permit greater blade droop when the fan is not
operating so long as the greater droop will not cause the
blade to hit an obstruction. If the fan has been operating for
a considerable length of time and previous inspections have
not disclosed wear at this point, it is possible that a recent
unusually high wind condition might have disturbed the
blades sufficiently to cause them to temporarily make repeti-
tive contact with the clevis while in operation.
3.1.6 CRACKS, DENTS AND CORROSION
Skin cracking may be caused by the tips dragging on the
fan ring, or it may be the result of long-term fatigue due to
continued operation under conditions of vibration or unbal-
ance as discussed in Section 3.3 which follows. Skin cracking
can also be caused by continued operation under overload
conditions as discussed in Section 4.3 Causes of Blade Over-
load.
Cracking in air seals can occur if the airseal has been
improperly installed. See Section 2.3. Check to be sure the
resilient washers are present and the nuts properly tightened.
The fatigue strength of materials, whether metal or plastic,
may be lowered by long-term exposure to water.
Dents in blades are caused by objects falling into the fan
or the fan striking some obstacle. Minor dents may some-
times be repaired by drilling a small hole in the center of the
dent and pulling outward on the blade skin. Blades may be
ordered from the factory for replacement. If there is any
evidence of this type of damage, the hub should be carefully
inspected as discussed in Section 3. 1.7 which follows.
The Type 5052 aluminum, a marine alloy, used as the
blade material on Moore fans works well with either fresh or
sea water. Waters that are acid, alkaline, or contain copper
salts, however, should be avoided for all aluminum alloys. If
you have questions regarding the suitability of the fan mate-
rials under certain water conditions, please contact the fac-
tory.
3.1 PERIODIC INSPECTION
MAINTENANCE
