Moore 5500 User manual

Contents
2.0 INSTALLATION........................................................................................................................................................ 2
2.1 GETTING STARTED ........................................................................................................................................ 2
2.2 INSTALL HUB AND AIR SEAL ..................................................................................................................... 3
2.3 INSTALL AND ADJUST BLADES ................................................................................................................ 4
2.4 START-UP PROCEDURES ............................................................................................................................. 5
3.0 MAINTENANCE ....................................................................................................................................................... 6
3.2 ANNUAL INSPECTION.................................................................................................................................. 7
3.3.3 BELT DRIVE UNITS .............................................................................................................................. 7
3.4 WARRANTY ........................................................................................................................................................ 8
3.5 PARTS LIST......................................................................................................................................................... 9
4.0 OPERATION............................................................................................................................................................ 10
4.1 AERODYNAMIC ABUSE.............................................................................................................................. 10
4.1.3 ABNORMAL CONDITIONS ............................................................................................................. 10
4.2 BLADE OVERLOAD ...................................................................................................................................... 11
4.3 CAUSES OF IMPROPER BLADE LOADING .......................................................................................... 12
4.4 CHECKING BLADE LOAD .......................................................................................................................... 13
4.4.2 TYPICAL TEST CURVES ..................................................................................................................... 14
4.5 DAMAGING OPERATING CONDITIONS ............................................................................................. 15
4.5.3 OBSTRUCTIONS ................................................................................................................................... 16
OWNER'S MANUAL
MODEL 5500 FANS ENGINE DRIVE FANS
OWNER’S MANUAL
INSTALLATION
MAINTENANCE
OPERATION
MOORE FANS LLC, Marceline, MO 64658 Phone (660 ) 376-3575 FAX [phone] Page 1
TMC-672-(Rev D) - 12/01

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MOORE FANS LLC, Marceline, MO 64658 Phone (660 ) 376-3575 FAX [phone]
covered by that Job Number so that, in future years,
reference to the Fan Specification Sheets provided will
identify the characteristics of each individual fan.
Moore keeps records indexed by serial and job
numbers of all fans produced for at least forty years in
order to provide proper maintenance advice and infor-
mation on spare parts and replacements.
2.0 INSTALLATION
2.1 GETTING STARTED
2.1.1 FAN IDENTIFICATION
Every fan, or group of identical fans, is assigned a Job
Number. This number will be found on Section 1.1 Fan
Specifications inserted in the envelope on the inside cover
of this manual. If non-identical fans are shipped together,
a Job Number is assigned to each fan or group and a set of
Order Information Sheets will be included for each Job
Number.
The Job Number is written in semi-permanent ink on
each blade, hub and air seal. All fan parts bearing the same
Job Number are entirely interchangeable. (Blades of the
same Series and Diameter are also interchangeable be-
tween Job Numbers.)
Fan components covered by more than one Job Num-
bermaybecratedtogether. TheJob Number that is written
on each part, however, will make sorting simple.
Each individual fan produced by Moore is assigned a
Serial Number. This Serial Number is embossed on a
permanentmetaltag andattachedto eachfanhub. TheFan
Specification Sheet provided for each Job Number lists all
of the individual Serial Numbers of the identical fans
1.0 ENGINE DRIVE FANS OWNER'S
MANUAL
1.1 ABOUT THIS MANUAL .......
Moore is as interested, as are its customers, that
Moore fans operate at top efficiency for many, many
years. This manual has been written to achieve that
result and is based on more than fifty years of experi-
ence as a manufacturer of axial flow fans.
Moore fans represent the highest degree of axial
fan development and are in all respects, regardless of
price, the finest obtainable for their intended purpose.
As for any fine equipment, certain precautions are
necessary and certain abuses must be avoided in order
to insure the best performance over the longest period
of time If you have any questions regarding the instal-
lation or operation of your Moore fan(s), please contact
the Company for assistance.
1.2 INSPECTION
All Moore units are carefully balanced, inspected
andpacked at the factory. If any damage is evident
before or after unpacking, the delivering carrier
should be promptly notified so that an inspection
may be made by the claims adjustor. It is the
responsibility of the consignee to file damage
claims with the carrier. Although Moore will not
be responsible for shipping damage, it is requested
that any damage, even of a minor nature, be re-
ported to the factory at once.
2.1.2 PLANNING THE INSTALLATION
The sequence given for the installation may be
changed if the conditions warrant. For example, the air
seal may be installed on the hub before the hub is
installed on the drive shaft. (In fact, for inverted fans,
it is necessary to install the air seal first.) The installa-
tion should be planned before beginning so that the
steps required are taken in the most convenient order. If
you need information not found here, please contact
Moore.
1.3 IDENTIFY YOUR FAN’S FEATURES
The installation instructions which follow will
include some steps for installing fans with features
not provided on you unis(s). Section 2 Getting
Started should be read carefully before installation
begins. Moore fans have several unique features.
INSTALLATION

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2.2 INSTALL HUB AND AIR SEAL
Note: Some air seals are provided with more mounting
holes than may be required. This is done intentionally to
make the air seals more interchangeable between units.
For example, an air seal with 8 mounting holes can be
used with either a 4-blade or an 8-blade unit.
To install the hub:
If the (3) stainless steel bushing studs are not already
installed in the fan hub, install them at this time. Hand-
tighten only.
Slip the bushing onto the shaft and check the key for
proper fit. Be sure the shaft is completely through the
bushing.
Carefully clean the bore of the hub and the outside of
thebushingwitha clean, drycloth. Usenolubricants inthis
installation. Use of lubricants can cause hub breakage.
Do not clean or alter the lubricant coating on the hex
nuts.Lift the hub by grasping the hub tubes. Do not lift the
hub by grasping the air seal.
Install the fan hub on the bushing with the studs
extendingthrough thebushingflange. Placethestudnutson
thestuds andtightenthenutsalternately,keepingthepullon
all of them as nearly equal as possible while drawing the hub
onto the bushing until the bushing tightly grips the shaft.
Cautionshouldbeusedtopreventthehubfromcockingon
the bushing.
Tightenthenutsto the torque showninthetableat left.
Do not over-torque. Excessive torque can cause hub or
bushing breakage.
On orders consisting of more than a small number of fans,
theairsealsare cratedseparatelyandmust beinstalledinthe
field.Whenfieldinstalled,the airsealmaybeinstalledonthe
fanhubbeforethehubis installed on the bushingifitismore
convenient to do so. The air seal, however, must not be
used to lift the hub.
HubOnlyWithoutAirSeal Air Seal Installed on Hub
FAN
HUB
SHAFT
Q D BUSHING
STAINLESS STEEL
BUSHING STUD STAINLESS NUT
(Specially Coated)
BLADE
TUBE
HUBINSTALLATIONONQDBUSHING
AIRSEALINSTALLATIONONHUB
RESILIENT
WASHER
ALUMINUM
WASHER
ALUMINUM
WASHER
RESILIENT
WASHER
CLEVIS
AIR
SEAL CLAMP
STUD
HUB
TUBE
ALUMINUM NUT
To install the airseal:
Locate the air seal installation hardware in the plastic
bag taped to one of the hub tubes. Place one resilient washer
on each bolt or stud as shown in the drawings at left. Place
the air seal onto the bolts or studs and install the remaining
hardware, following the sequence shown in the drawings.
Do not lubricate this end of the studs.
Note that the diameter of the resilient washers, before
they are compressed, is slightly less than the diameter of the
aluminum washer. Tighten each nut until the resilient
washer's diameter is the same as the aluminum washer. Do
not overtighten. Overtighteness exists when the resilient
washerhasexpandedin diameterlargerthanthe diameter of
the aluminum washer.
BUSHING
SIZE
SF
E
J
FT-LBS
20
40
90
M-KGS
2.77
5.53
12.44
MAXIMUMTORQUE
INSTALLATION

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2.3.1 INSTALL BLADES ON ENGINE DRIVE FANS
2.3 INSTALL AND ADJUST BLADES
BLADE
and insert the clevis bolt. Screw the nut onto the
projecting bolt threads loosely. When shipped
from the factory, the nut threads and the washer
face of the nut are coated with a low-friction grease.
It is essential that sufficient grease for proper
lubrication is retained on the nut face.
Complete the installation of one blade by hold-
ing the blade so that the blade extends straight out
from the hub tube and clevis. Holding the blade in
thisposition,tightenthe nut usingatorquewrench
set to 100 ft-lb (14 m-kg).
After installing the first blade, manually ro-
tate the fan while moving the blade tip in and out to
be sure the blade clears the ring or throat at all
points. When the blade is held in alignment with
the blade tube (that is, straight outward from the
hub), it should clear the fan ring by a distance
adequate to provide for any relative motion be-
tween the fan wheel and the ring. Excess clearance
betweentheblade tipsandthe ring,however,should
be avoided to prevent backflow which seriously
reduces fan efficiency.
Install the rest of the blades so that they are
identical with the first blade. Torque all clevis
nuts to 100 ft-lbs (14 m-kg). If blades are installed
properly, they will return to their undisturbed po-
sition if the tips are pressed in the axial direction
with moderate force (10 to 20 lb).
BEFORE INSTALLING BLADES. . . .
Check to see that the hub is level. If the drive shaft
is not truly horizontal, causing the hub to be cocked, it
will be difficult to adjust blade angles accurately. Ec-
centric rotation of the fan can also cause serious vibra-
tion problems.
If misalignment, vibration or unbalance in the
system is present, it will be more easily identified and
corrected at this time.
Moore fan blades are carefully balanced to the same moment
at the factory. Any blade of the same series and diameter may
be installed on any hub furnished on the job. They are
completely interchangeable.
Moore fans are designed for engine drive and
other applications with the more severe requirements
of this service. Proper installation, with particular
attention to tightening nuts to the specified torque, is
essential to maintain the design integrity of these
units.
To install, remove the clevis bolt and nut from the clevis
ears. Clean any grease or dirt from inside the clevis ears and
inspect the blade resilient mount faces. Note that these
mounts are 3" long and have a rough, high-friction layer on
the faces. Other mounts should not be used on Engine Drive
Fans.
Align the mount hole with the holes in the clevis ears
CLAMP
CLEVIS
CLEVIS BLADE BOLT
RESILIENT
MOUNT
HUB TUBE
CLEVIS BOLT NUT
BOXSECTION
CLAMP NUT
INSTALLATION

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Before starting the fan, manually check all bolts or
nuts to see if they are tightened. Take care not to exceed
the stated torque limits.
Manually rotate the fan while checking each blade
for proper clearance.
Start the fan and watch it in operation. All blades
should move to the same operating position, indicating
that the blade angles are properly set and that all blades
are equally loaded. If vibration or unbalance is evident,
see Section 3.3.
After the fan has been operating for several minutes,
stop the fan and observe the blades as the fan comes
to rest. All of the blades should return to their origi-
nal position at the same rate.
Inspect the inner surface of the fan ring and the
blade tips for any indication of scoring.
The horsepower given on the Fan Specifications
is the calculated horsepower (at the fan shaft) that is
required for the specified performance. Consult the
factory or the fan curve before increasing the blade
angle for the fan to consume more than the specified
horsepower.
2.4 START-UP PROCEDURES
2.3.2 ADJUST BLADE ANGLE
protractor level on the flat upper or lower surface of the
clevisasshownin theillustrationatright. (This isthepoint
of measurement of the blade angle stated on 1.1 Fan
Specifications.) Make a permanent record of the final
clevis angle selected and take care that all blades on the
fan are set at the same angle. A typical adjustment
may be +/- 3o. The maximum recommended clevis
angle is 15o.
HUB
TUBE CLEVISBLADEBOLT
CLEVIS
CLEVISBOLTNUT
HUB TUBE BOLT
Hubs are shipped from the factory with the clevises set
for the blade angle indicated by the design performance. A
change in blade angle is sometimes necessary, however, to
adjust to actual site conditions. Failure to adjust the blade
angle when required may result in blade overload. The
causesofimproper blade loadingareexplainedin Section4.3
of this manual. Section 4.4 "Checking Blade Load" provides
a simple method of determining the maximum blade angle
allowable in terms of static pressure vs blade angle. Please
refer to these sections before increasing blade angle.
Remove each blade from the
fan before beginning blade
angle adjustment by remov-
ing the clevis blade bolt and
nut. Manually rotate the fan
until one of the hub tubes is in
a horizontal position. Use a
leveltobesurethetubeisheld
or locked in this position. If
the tube is not horizontal, the
blade angle will not be cor-
rectly measured during ad-
justment.
Loosen the Hub Tube
Bolt just enough to allow the
clevis to be turned. Place a
WARNING: The fan is designed to consume the
horsepower stated on the Fan Specification Sheet. The
engine drive typically produces far more power than
thefancanabsorb.Toogreat an increase in blade angle
can cause serious blade overload which will stall the
blades. In this condition, the fan will actually deliver
less air and blade life may be shortened. Blade load
considerations are discussed in Section 4.0 Operation
in this manual.
Retightenthe Hub Tube Bolt to 150 ft-lb (21 m-kg).
NOTE: It is essential that bolts are properly tightened
for engine drive operation. Recheck the blade angle after
tightening.
Reinstalltheblades following theinstructionsunder
Section 2.3.1 on the preceding page. Be sure that suffi-
cientgrease remains on the clevis boltnutfacesandthat
they are tightened to the proper torque of 100 ft-lbs (14
m-kg).
NOTE: Some recent fan models are furnished
with a scale marked in degrees attached to the hub
tube and an arrow machined on the clevis. In this
case, blade angle is set by simply aligning the arrow
with the mark for the desired angle. The hub tube
may be in any position.
INSTALLATION

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3.0 MAINTENANCE
3.1.1 PURPOSE
Fan failure is most likely the result of destructive repeti-
tivestressactingoveraperiodof 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 accor-
dance with the severity of service and a suitable inspection
schedule 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 ANGLE AND RUNNING POSI-
TION
Turn off the unit and watch the blade tips. A looseness
in the hub tube 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 replace-
ment.
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 over-
load 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 repetitive contact with the clevis while in
operation.
3.1.5 CRACKS, DENTS AND CORROSION
Skincrackingmaybecausedby the tips dragging onthe
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 2.2. Check to be sure the
resilient washers are present and the nuts properly tight-
ened.
Thefatiguestrengthof materials,whethermetalor 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. 1.6 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
materials under certain water conditions, please contact the
factory.
3.1 PERIODIC INSPECTION
3.1.6 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. Hub tubes
cannot be replaced in the field on manual fans and a new
hub should be ordered.
Bushings are frequently cracked during a fan wreck
andshouldbe carefullyinspected.Damage mayoccurto 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
MAINTENANCE

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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
fanistheleastlikely causeofvibration. Allfancomponentsare
balanced to within ±0.2 ft-lbs.
If the fan is in an unbalanced condition, the frequency of
vibrationofthestructurewillbe that of the RPM ofthefanand
isquitelow. Inthecase oflargefans,thefrequencyisoften 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 eccen-
trically, throwing the weight of the fan off-center, resulting in
unbalance of the frequency of the fan RPM.
After all checks have been made and the fan is still deter-
mined to be unbalanced, field balancing may be accomplished
as described in section 3.3.6.
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
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
Theyearlyinspection shouldbeaverythorough 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
frettingeffectandthe resilient mountmaterialwillshowsigns
of extruding from the cavity. If these indications are not
apparent, replace the blade and continue normal operations.
Inspecttheblade tipsforanysigns ofcrackingand thefan
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.) These accumulations may
significantly 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.
thestructureon whichthedrive wasmounted.By contrast,
it would be unlikely that the drive shaft of a fan, of perhaps
25 HP, would be supported on bearings rated less than
2000 or 3000 pounds radial load. For higher horsepowers,
the bearing capacity would be correspondingly increased.
From this it is evident that speed reducer or drive shaft
bearing failure could never be caused by moderate or even
objectionable fan unbalance.
As with any industrial equipment, before entry into fan chamber, strict adherence to ALL
Lock-out / Tag-out procedures is well advised!
3.3.4 ROUGH GEARS
Continued operation on rough gears and bearings is
almost certain to develop cracks in the blade skins. Rough
gears may be of two types:
1. Rough or failed bearings in the drives or gears will
result in a high frequency vibration being transmitted into
the fan where some areas of the skin will respond to the
frequencies applied. Cracks will appear in the blade skin
and in some areas, the skin may actually fall away.
2.Theothertypeofroughgear occurs when the output
shaft accerelates and decelerates with each pinion tooth
engagement. With six tooth pinion and a motor speed of
1800 RPM, or 30 cycles per second, this gear misalignment
impresses upon the fan a vibrating frequency of 30x6=180
cycles per second. If the engagement of teeth is also
included, the frequency is 360 cycles per second. This type
of high frequency vibration is at least as serious as that
caused by bad bearings.
3.3.3 BELT DRIVE UNITS
The more common causes of vibration in belt drive
units are not the drives themselves but the result of shafts
that are too flexible or non-rigid supporting members.
Vibration can be caused by misalignment of the sheaves or
poorly adjusted belt tension. Consult the manufacturer of
the drives for information. The quickest way to identify the
cause of vibration in belt drive units is to operate the fan
with the blades removed.
MAINTENANCE

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3.3.6 FIELD BALANCING
Unbalance in older fans may develop because of some
structural change or by installing one new blade on an old
fan where the existing blades had changed in weight in the
course of operation.
Use wire to attach a small weight in succession to each
of the clamp studs until the best location for the weight is
found. The weight should then be increased or decreased
until the best balance is achieved. The permanent weight
may then be secured to the clamp stud, clevis, or hub tube,
whichever is the most convenient for the type and shape of
weight to be used. One or more pieces of metal shaped like
a washer could be placed over the clamp stud, on the hub
tube, behind the clamp stud, or over the threaded portion of
the clevis. Aluminum or stainless weights should be used
and weights should not be attached to the blade skin.
3.3.5 THROAT FLUTTER
Any fan that is effectively moving air at the tips of the
blades will develop a reduced pressure area (or suction) on
thefan throator ringat thetip ofthe blade.This suctiontends
todrawthethroattowardthe tip of each blade,whichmeans
that a four blade fan would tend to draw the throat into
somethingapproachingasquare while asixbladefanwould
draw it into something resembling a hexagon, etc. Since the
fan is rotating, the effect on the throat is that of continually
drawing it into a rotating polygon. The resulting throat
flutter is frequently mistaken for fan unbalance.
A substantial throat or ring will be sufficiently rigid that
flutter will not exist. A weak or flexible throat, particularly
when used with a fan of a low number of blades, will be
greatly affected by this type of vibration. Throat flutter is
easily detected due to the fact that it is invariably of a
frequency of the fan RPM times the number of blades on the
fan. Throat flutter will cause no damage to the fan so long as
the throat does not disintegrate and fall into the fan blades.
It may be eliminated by stiffening or bracing the throat.
If in doubt that throat flutter is the cause of vibration,
reduce the angle of the blades until the fan is doing little or no
work. If the vibration ceases under this condition, it is certain
that throat flutter is present when the blades are loaded.
Moore Fans LLC (the Seller) warrants only to
Buyer, as its purchaser for resale, that the fans manufac-
tured and sold by Seller to Buyer under this Agreement
will be free from all defects in material and workman-
ship under ordinary use for a period of two (2) years
from the date of shipment or one (1) year from the date
the fan is installed on a customer's premises, whichever
occurs first. This warranty period shall apply only if
Seller receives written notice of any defect within the
warranty period. Upon receipt of such notice, Seller, at
its option, may require Buyer to return the fan at Buyer's
cost to Seller for inspection by Seller. If the fan is found
to be defective on inspection by Seller, as a sole and ex-
clusive remedy, Seller will, at its option, either repair or
replace the fan. This warranty shall not apply to dam-
age on account of misuse, neglect or accident or ship-
ping damage, or if repairs or part replacements have
been made or attempted without Seller's prior written
authorization. SELLER SHALL NOT BE LIABLE IN ANY EVENT
FOR ANY INCIDENTAL OR CONSEQUENTIAL DAMAGES FOR BREACH
OF THIS OR ANY WARRANTY. THIS WARRANTY IS IN LIEU OF ALL
OTHER GUARANTEES OR EXPRESSED WARRANTIES AND ALL IM-
PLIED WARRANTIES, INCLUDING THE IMPLIED WARRANTIES OF MER-
CHANTABILITY AND OF FITNESS FOR APARTICULAR PURPOSE. DUE
TO THE VARIETY OF CONDITIONS UNDER WHICH THE FANS MAY BE
USED, RISKS OF RESULTS OBTAINED FROM USE OF THE FANS,
WHETHER USED ALONE OR IN COMBINATION WITH OTHER PROD-
UCTS, IS ENTIRELY BUYER'S. THE ABOVE LIMITATIONS ON DAM-
AGE AND EXCLUSION OR LIMITATION OF IMPLIED WARRANTIES ARE
NOT APPLICABLE TO THE EXTENT PROHIBITED BY STATE LAW.
3.4 WARRANTY
MAINTENANCE

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DESCRIPTION
SHOP
PART
NO.
DWG.
NO.
1 913 22 MM ALUMINUM CLEVIS BOLT
2 644 SMALL CLEVISCLAMP
3 914 22 MM ALUMINUM CLEVIS BOLT NUT
4 912 HUB TUBE BOLT
5 608 CLAMPSTUD
6 169 16 MM ALUMINUM NUT
7 931 CLEVIS
8 939 LARGE MOUNT (3” LONG)
9 151 5/8” ALUMINUM FLAT WASHER
10 52 5/8" RESILIENTWASHER
11 1345 10MM SS STUD FOR QDSF BUSHING (3)
1347 12MM SS STUD FOR QDE BUSHING (3)
1558 16MM SS STUD FOR QDJ BUSHING (3)
12 QDSF, QDE OR QDJ TYPE BUSHING
13 1346 10MM SS NUT FOR QDSF BUSHING (3)
1348 12 MM SS NUT FOR QDE BUSHING (3)
1559 16 MM SS NUT FOR QDJ BUSHING (3)
14 911 ANCHOR PLUG
MAINTENANCE
5
8
9
6
6
10 9
13
11 12
1
2
13
7
214
4
3.5 PARTS LIST
NOT TO SCALE: SOME DIMENSIONS
AND ANGLES HAVE BEEN
EXAGGERATED FOR CLARITY

Page 10 TMC-672-(Rev E) - 05/02
MOORE FANS LLC, Marceline, MO 64658 Phone (660 ) 376-3575 FAX [phone]
4.0 OPERATION
4.1.1 ABOUT THIS SECTION . . . .
It is widely acknowledged that the kinds of mechanical
abuse described on the preceding pages are destructive for
all types of operating equipment. It is less well recognized
that — for fans — aerodynamic stresses are an even more
serious hazard. This section deals with the causes of destruc-
tive aerodynamic stresses and how they can be avoided.
Although this information is given primarily for the
benefit of operators of Moore equipment, it may be applied
to fans of any manufacture.
Unlike smaller fans, which are typically furnished
complete with their surroundings, the large fan wheel is
supplied as an unprotected component of the system and is
installed in innumerable types of surroundings. Not only do
the types and conditions of the drives for these fan wheels
vary widely, but the entrance and exit conditions and the
enclosure for the wheel assume a myriad of possible combi-
nations. In designing his product, the manufacturer of fan
wheels must anticipate the operating conditions based upon
his knowledge of what is reasonable and customary for the
industry. He may over-design for abnormal stresses only
until the practical limit is reached to avoid excessive weight,
cost and inefficiency.
4.1.2 NORMAL OPERATING CONDITIONS
The fan manufacturer assumes a fairly reasonable
atmosphere for the operation of his product, including the
following:
The fan selection will be reasonably in line with the
performance the unit is expected to maintain, with an
adequate blade area for the pressure required at the
given RPM. Blades will not be loaded beyond their
capacity to maintain air flow.
A fan ring will be provided that is round, rigid and of
a depth at least sufficient to cover the tips of the blades.
Tip clearances will be uniform and controlled.
The approach air will represent a relatively uniform
and axial flow with, of course, some unavoidable
turbulence expected. Adequate open area will be pro-
vided at the inlet of the fan.
Major obstructions will not be present at either the inlet
or discharge of the fan.
The RPM of the fan will be within the design limits.
The relative direction and velocity of approaching air
to the blades will be fairly constant and protection will
be provided from extreme wind conditions.
Under such conditions, the unit stresses in the blades
would not be expected to vary more than plus or
minus 50%. Fan design based on such assumptions is
entirely reasonable and, with proper drives and in-
stallation conditions, has proven highly successful.
4.1.3 ABNORMAL CONDITIONS
Abnormal operating conditions result in destruc-
tive repetitive stresses that can seriously shorten fan
life. The aerodynamic abuses discussed in this section
can cause repeated flexing of the fan blades and hub.
Violent displacement of the resiliently mounted Moore
fan blades may occur — a greater displacement than
would occur in rigidly mounted blades. The resilient
mounting, of course, minimizes the structural unit
stresses which would be transmitted to the root of the
blade and into the hub and drive. Although Moore
units may be expected to resist greater stress than units
of conventional design, such repetitive stresses may
exceed the capability of the resilient mounts to absorb
them. If so, fatigue of the mounts and metal may
develop, adjusting linkages may wear, and ultimate
failure becomes a possibility.
Some of the abuses set out in the following text
are far less important than others. All of them may
occur in varying degrees.
Specifically, abuse due to serious repetitive
stresses can lead to mount failure and, if carried to
extremes, can cause clevis breakage and failure in the
box section due to the end of the box section repeatedly
striking the clevis as the blades are violently displaced.
In units of other manufacture with rigidly mounted
blades, repetitive stresses of this type may lead to blade
breakage, probably near the root or at the point of
attachment to the hub where stresses are highest, or
may lead to failure of the hub itself. The resilient mount
design, unique with Moore fans, dampens these vibra-
tional forces and results in a fan that is far less vulner-
able to failure from these conditions than other units
with rigidly mounted blades. Even so, extreme condi-
tions can cause damage.
A well-designed fan can be expected to operate
for many years without trouble under normal opera-
tion as described above. The extreme repetitive
stresses described below, however, will certainly
reduce the life of the fan, causing failure many years
sooner than would occur if the fan were operated as
intended. Fortunately, these destructive conditions
are readily observable to someone who is knowl-
edgeable about them, and they can be corrected with
reasonableeffortandexpense once theyareobserved.
4.1 AERODYNAMIC ABUSE
OPERATION

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4.2 BLADE OVERLOAD
Of all the aerodynamic abuses to be avoided in the
operation of a fan, the most important is that of
overloading the fan blades. Blade overload occurs
because of insufficient blade area: In other words,
when there is an inadequacy in the number of blades
on the fan selected.
The Moore system of rating is based upon the
pressure that each blade will produce at a given RPM
with good efficiency. This pressure is called 100%
blade load. When blade load exceeds 110%, the fan will
not only operate at lower efficiency, it may be subject
to structural damage as well.
In selecting a fan, the total pressure divided by
the pressure to be produced by one blade determines
the number of blades required for the anticipated
performance. Whenever information is available,
Moore checks the selection. Even so, underestimation
of the pressure requirements by the system designer,
or changes in the operating conditions over time, may
result in overload conditions.
Why is a blade overload condition of such con-
cern? We are all aware of the fact that an airplane
traveling at a given speed can carry only a certain load.
If the speed of the airplane is decreased or the load
increased, stalling flow over the wing will occur. In the
case of an airplane, approximately two-thirds of the
lift provided by the wing is the result of the air flow
over the top or convex portion of the wing. Lift is
provided as a reaction to the flow of air being acceler-
ated and deflected downward as it passes over the
wing. A negative pressure area is thus formed on the
top surface of the wing which tends to lift it upward.
So long as air flow over the wing is smooth and
clings to the surface of the wing, little turbulence is
present. When the load is increased, or the speed
decreased, the angle of the wing to the air stream must
be increased to a point where the air flow breaks away
from the upper surface of the wing. This is known as
stalling or burbling flow, since the air, instead of
clinging to the wing, breaks away near the leading
edge and leaves what might be called a turbulent void
above the upper wing surface, nullifying the acceler-
ated flow which was responsible for the greater part of
the lift of the wing.
When this occurs, the wing loses a large portion
of its lift. Flow, however, will re-establish briefly and
break again, the cycle being repeated continuously,
resulting in a severe vibration throughout the aircraft
as the flow alternately makes and breaks. Anyone who
has experienced a stall in an airplane will be familiar with
this violent phenomenon.
A fan blade is no different than an airplane wing
except that the air usually is being deflected upward
rather than downward, the convex side of the blade
being the lower surface rather than the upper surface as
in the case of an airplane. The result of blade overload
is identical: When blade load exceeds that allowable, a
violent vibration will take place in the blade as the
laminar, or uniform, flow makes and breaks perhaps
many times a second.
Another way of looking at this problem is to
consider that the available number of blades are set at
too steep an angle to be able to move air at the axial
velocity which is necessary to maintain a smooth flow
over the convex surface. In other words, to move air at
the velocity necessary for this blade angle, plus over-
coming the static resistance of the system, the total
pressure which would have to be maintained for an air
flow corresponding to this angle is greater than the
total pressure capability of the given number of blades
at this RPM. Such a condition can only be corrected by
decreasing the blade angle until smooth flow is ob-
tained or by increasing the number of blades and the
total pressure potential of the fan until the fan’s pres-
sure potential equals the pressure necessary to move
the specified quantity of air through the system.
Continued operation under conditions of stalling
flow, or blade overload, will significantly shorten the
life of the fan. Operation under these conditions will
also reduce efficiency to a ridiculously low figure. See
the chart under Section 4.4 Checking Blade Load which
follows. Note that although air flow remains constant
or decreases, horsepower continues to increase with
increased blade angle.
In conclusion, if a given fan, in a given installation,
can only absorb forty horsepower, for example, the blades
may be pitched up to consume fifty horsepower without
any increase in air delivery, and possibly with a decrease. As
a result, the extra ten horsepower is totally wasted -- perhaps
worse than wasted. It is good practice to select a sufficient
number of blades so that blade load will amount to slightly
less than 100% of full blade load when consuming 100% of
the rated fan horsepower. There are a number of reasons
for allowing this safety factor which are set out in detail
below.
AIRFLOW IN NORMAL FLOW
Downward flow provides lift to the wing AIRFLOW IN STALLING FLOW Note lack of air deflection downward.
OPERATION

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MOORE FANS LLC, Marceline, MO 64658 Phone (660 ) 376-3575 FAX [phone]
4.3 CAUSES OF IMPROPER BLADE LOADING
4.3.1 VARIATION FROM PREDICTED CONDITIONS
Although those who design air coolers and cooling
towers undoubtedly do their best to accurately state the
calculated static resistance of the system, a number of
factors may cause the actual conditions to vary from the
design conditions. When a variation occurs, it may be
found, upon testing, that the static pressure for a given
volume through the system is higher than anticipated. In
this case, the number of blades provided may be inade-
quate to meet the performance. On the other hand, the
static pressure may have been overestimated and excess
blade area provided, resulting in a fan with unutilized
capacity operating at low efficiency.
Inadequate Blade Area: The blade angle is selected
to move the anticipated volume of air and the number of
blades is selected to maintain the total anticipated pressure
required to move this volume at a given RPM. If the static
pressure turnsoutdobehigherthan predicted, the fan may
then be operating in an overload condition. If the RPM
cannot be increased, the only solution to this condition is to
reduce the blade angle until the fan can carry the then
reduced volume at the originally anticipated pressure.
Since reducing the volume, while holding the total pres-
sure as originally anticipated, can only reduce the horse-
power, it is then impossible to consume the horsepower
originally intended without overloading the fan. This is
one of a number of reasons for providing some safety factor
in blade loading at the time of original fan selection.
Excessive Blade Area: Occasionally, an excessive
number of blades may be specified in the interest of making
a conservative selection. If the static pressure has been
overstated, the theoretical number of blades will be greater
than needed. This theoretical number of blades is usually
a fractional number and the actual number of blades used
must, of course, be the next larger integer, resulting in
some "safety factor" in the selection. If, in addition, a blade
or two is added as a "safety factor" or in anticipation of
increased future requirements, it may be impossible to
meet the original performance requirement efficiently. The
only way to provide the original performance and draw no
more than the original horsepower is to flatten the blade
angle. There is a limit, however, in how far the blade angle
may be reduced before further reduction will decrease
airflow without a further reduction in horsepower. For
belt drive units, the most practical solution to this problem
is to reduce the RPM of the fan.
4.3.2 EXCESSIVE TIP CLEARANCE
Unless the fan ring is very close to the tip of the blade,
air from the high pressure surface of the blade will flow
around the tip and nullify the negative pressure on the
underside of the blade for some distance in from the tip. For
a fan of, say, 12-ft diameter, the last 12 to 18 inches of the
blade could be producing no pressure whatever and per-
forming no useful function. The balance of the fan blade
toward the hub then must produce a higher pressure to
compensate for the portion near the tip.
Excessive tip clearance also leaves an unswept area
between the tip of the blade and the fan ring. Air that has
been pumped by the fan will return downward through
this unswept area at a velocity greater than that at which
it passed through the fan in the desired direction. This
condition adds even further to the requirements of the
portion of the blade which is doing the work and effi-
ciency will be greatly reduced.
With the loss of a foot at the tips of the blades, plus
the back flow between the tips and the ring, the 12-ft fan
in this example might be considered an effective 10-ft
fan. It would have to deliver sufficient air to satisfy the
performance requirements of the installation, plus the
amount of air which is returning in the void between the
tips and the throat. Under such circumstances, excessive
blade loading could occur even though the required
system pressure is not achieved.
4.3.3 POOR ENTRANCE CONDITIONS
Air will approach the fan from all possible direc-
tions, increasing in velocity as it nears the opening, then
accelerating rapidly as it enters. The air approaching
from the side must be turned through 90Oto enter a ring
whose entrance terminates in a flat plate. If the inlet end
of the ring projects some distance out, with approach
possible from all directions, a portion of the air must be
turned through 180O. The inertia of the approaching air
prevents it from turning sharply and advancing parallel
to the desired flow. It consequently swoops toward the
center, leaving the outer area of the fan with reduced
flow or even reverse flow near the ring.
The effect of poor entrance conditions is similar to
that previously described for excessive tip clearance in
that the effective diameter has been reduced and exces-
sive blade loading could occur even though the required
systempressureisnotachieved. Efficiencywillbe greatly
reduced.
4.3.4 EXCESSIVE DEFLECTION
The pressure which the fan can achieve is depend-
ent upon the square of the velocity of the blades relative
to the air. If the air could be moved into the fan in an axial
direction and passed through the fan into the discharge
without changing direction, the relative velocity of the
blades to the air stream would be the true velocity of the
blades at any point. This, of course, is not the case. For
the blades to accomplish work upon the air, they must
also deflect the air in the direction of rotation of the fan.
The air when rotated with the fan is moving with a
certain velocity in the same direction as the rotation of
the fan, which reduces the relative velocity between the
fan blades and the air by some portion of this rotational
velocity.
OPERATION

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02
4.4 CHECKING BLADE LOAD
One method of checking blade load is to run
a complete field test on the fan. Although labori-
ous, this method will provide ample proof so long
as neither excessive tip clearance nor poor en-
trance conditions are present. If either are present,
however, the conditions set out above under Sec-
tion 4.3.3 would apply and the fan could be over-
loaded even though the total pressure indicated by
the test was within the allowable blade loading.
A better, more convenient and simpler method
of detecting blade overload, or determining maxi-
mum allowable blade angle, is set out below. The
equipment needed is a wrench, a torque wrench, a
protractor and a draft gauge (or manometer).
All fans are shipped with the blade angle set for
the anticipated performance requirements furnished
to The Moore Company by the purchaser. This blade
angle is called out on Section 1.1 Fan Specifications.
This angle refers to the angle of the top or bottom of
the clevis with the horizontal. Hubs are shipped with
the clevises set at this angle.
To start the test, adjust the blades to an angle
of approximately half that called out on the speci-
fications or measured on the units. Connect the
draft gauge to as quiescent a spot in the plenum as
possible, preferably in the corner of the plenum
and either ahead of or following the fan, depend-
ing upon whether the application is induced or
forced draft. Since the figures obtained are purely
relative, it is not necessary that accurate static
pressure readings be obtained, but rather that the
readings taken represent a consistent series of pres-
sures at the point of reading chosen.
Start the fan and record on the chart provided
the blade angle and he static pressure indicated.
Advance the blade angle by one or two degrees
and repeat the performance, recording again these
4.3.5 CONCLUSION
As can be seen by the various points discussed
in this section, there are a number of complex factors
which tend to cause fans to be operated in a condi-
tion of improper blade loading which can shorten
fan life or lower efficiency. When blade angles are set
to consume the specified horsepower (at the fan
shaft), the resulting performance should be very
close to the specified performance. If this is not the
case and the problem cannot be identified or cor-
rected, please contact Moore for assistance.
readings. Keep increasing the angle and following
this procedure until the motor is fully loaded, in
which case the fan is able to consume full rated fan
horsepower without overload OR until the curve
which will have started on a definite slope begins to
approach the horizontal. It will be noted that the
static pressure will be consistently increasing with
increased blade angle until the blade loading reaches
maximum, at which point it will level off.
Subsequent increases in blade angle may have
quite different effects, depending on the individual
installation. The static pressure curve may merely
stay level or may drop off sharply. In rare cases, it
may level off and again start rising as the fan begins
operating as a centrifugal blower.
Typical examples are shown in dotted lines on
the chart opposite. Operation beyond the first point
of levelling, or in the area of the dotted lines, is
indicative of blade overload. Note that power con-
sumption load will continue to increase even though
the fan has passed into overload condition. The
maximum blade angle allowable is that which pro-
duces a static pressure about 5% below the point
where the curve becomes level. This represents a
safe loading, and the blades may be set and left at
this angle regardless of the location on the chart,
assuming the motor is not overloaded.
The point so selected will also approximate the
point of the most efficient operation of the fan. Due
to possible error in static pressure predictions, or in
readings which are intended only to be relative, as
well as other variables, the final blade setting chosen
may fall below or above the specified static pressure.
A typical performance chart is shown opposite
for a fan capable of a higher blade loading than
origianally specified. A blank chart is also provided
for your use.
Moore fans are designed in contemplation of a
maximum deflection of 50 degrees at the hub, decreas-
ing to a very small value at the tip. This deflection is
considered in the determination of the pressure which
may be provided by each blade over its full length. If
fans are selected, or if conditions exist, which cause the
deflection to exceed 50 degrees at the hub, the velocity
of the blades relative to the air is less than anticipated
and the blades will not provide the rated pressure
capablity of the fan, even though it does not reach the
full rated pressure.
OPERATION

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MOORE FANS LLC, Marceline, MO 64658 Phone (660 ) 376-3575 FAX [phone]
120
110
100
90
80
70
60
50
40
30
20
SELECTEDBLADEANGLE
STATIC
PRESSURE
BLADE ANGLE VS % RATED FAN HP
BLADE ANGLE IN DEGREES
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
1.2
1.1
1.0
.9
.8
.7
.6
.5
.4
.3
.2
STATIC PRESSURE
% RATED FAN HORSEPOWER
STATIC PRESSURE
FINAL % RATED FAN HP
Note in the chart above that static pressure (and air flow) has
reached its maximum at an 11 degree blade setting and blade
overload is beginning. With further increase in blade angle, any-
thing may happen, as indicated by the dotted extensions into the
shaded overload area. Note that the final selected blade angle is 5%
below the point where the static pressure curve becomes level.
Thehorsepowercurve hasbeenadded toillustratethepoint that
in an overload condition, horsepower will increase without in-
creased performance.
BLANK CHART FOR CUSTOMER USE
BLADE ANGLE IN DEGREES
FACTORY-SETBLADEANGLE
4.4.2 TYPICAL TEST CURVES
OPERATION
FULL LOAD
AMPERES

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THE EFFECT OF AIR LOAD ON HUB AND DRIVE
Moore fan blades are attached to the hub by a
pivot. As the fan rotates, centrifugal force causes the
blades to rise (as do the blades of a helicopter). The air
load (FA) is uniform over the blade, but there is a point
(shown on the blade in the drawing below) where, if the
total load were applied at that point, the effect would be
the same. The resultant of the air load (FA), assumed in
this example to be downward, and the horizontal cen-
trifugal force (FC) is the force on the blade (FB). The blade
automatically positions itself in the direction of this
In conventional fans with rigidly attached blades, the
bending moment at the shaft due to the air load is equal to
the load (FA) multiplied by the distance from the fan
centerline to the point of application of the force on the
blade (RF). This moment will be from 2 to 4 times as great
as that produced by the Moore fan under the same condi-
tions.
Also of concern with the conventional fan is the
bending moment due to the air load at the point of
attachment of the blades to the hub since this is usually
the structurally weakest area of the fan. The moment due
to the air load at this point is the load (FA) times the
distance (D). For the Moore fan, this moment is zero since
the blades are attached at the pivot point.
A more complete discussion of the Moore fan de-
sign can be found in Moore’s General Catalog.
force with the result that the force is translated inward to
the pivot point, as illustrated by the dotted line. The effect
of this arrangement is exactly as if the total air load (FA)
were applied at the pivot point rather than at the point
outward on the blade. The maximum bending moment
applied to the shaft by the air load is equal to the load (FA)
multiplied by the distance from the fan centerline to the
pivot point (RP).
may be increased by as much as 45Ounder high wind
conditions.
In the case of a fan blowing inward in a short ring,
the condition is even more critical. In such an installation,
the air on the inlet side of the fan has a horizontal velocity
which may be quite high. It is necessary for the fan to
pick up this air and direct it inward. In a strong wind, the
angle of air moving through the fan may be increased
4.5.1 GENERAL
Any condition which causes repeated blade loading
and unloading is detrimental to fan performance, both in
terms of efficiency and structural durability. Normal
obstructions, of course, must be expected in the air stream.
There are certain conditions, however, which may be
avoided by reasonable attention to the points briefly dis-
cussed in this section. Additional information on the
importance of inlet and discharge conditions can be found
in Moore 's General Catalog.
Ideally, air should approach a fan in an axial direc-
tion and at a uniform velocity over the area of the fan. Air
approaching a fan at an angle tends to increase the rela-
tive velocity of the blades to the air on one side of the fan
and decrease the relative velocity on the other side. This
means that the fan blade during one-half of its revolution
is picking up a heavier air load due to the higher relative
velocity and, through the other half of its revolution, a
lower air load as it goes "down wind". The net result is a
repetitive loading and unloading of the blades at each
revolution of the fan. This condition can be quite serious
if the velocities are high and the angle of approach devi-
ates considerably from axial.
4.5.2 WIND
With a vertically mounted fan blowing outward
into the wind and surrounded by a short fan ring or stack,
high winds may cause some concern. The farther the ring
extends beyond the fan, the less effect would be expected
from wind. It is a fact, however, that wind across the face
of the ring will affect the direction of air flow well down
into the ring. In the case of a fan installed near the outlet
of the ring, the direction from axial of the fan discharge
4.5 DAMAGING OPERATING CONDITIONS
more than 45O.
The illustration above assumes a fan operating with
a tip speed (VB) of 10,000 feet per minute (114 miles per
hour) with a horizontal component of wind velocity (VW)
of 20 miles per hour. Note that the velocity (VR) of the fan
blade relative to the air varies by a factor of 1.43. The
blade load varies as the square of this velocity, or 2.05.
OPERATION

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In this rather common wind condition, then, it can
be seen that the blade load on the side where the blade
is going against the wind will be double the load on the
side where the blade is going with the wind. In a 40
mile per hour wind, the blade load would vary by a
factor greater than 4. In a 60 mile per hour wind, the
load would vary by a factor of more than 10! It is obvi-
ous that operation under such conditions will impose
tremendous repetitive loadings on the fan blades.
In areas of unusually high wind velocities, it may
be advisable to shield the fan in some manner.
4.5.3 OBSTRUCTIONS
Obstructions of one type or another in the air
stream, ahead of or beind the fan, are to be expected. In
fact, it would be virtually impossible to eliminate all
obstructions. Structural supporting members, founda-
tions and the like, need not be of serious concern al-
though all obstructions, even small ones, will increase
the static pressure and must be taken into considera-
tion by the system designer in specifying the fan per-
formance.
The total free area from which the fan can draw
air should be twice the net area of the fan (fan area mi-
nus hub area). In other words, the air approaching the
inlet of the fan should have no more than half the ve-
locity of the air passing through the fan. This area should
be distributed reasonably uniformly. It would be unwise
to attempt to operate a fan with one-half or one-third of
the fan area completely blanked off. Such a condition
would cause stalling of the fan blade through one-half the
revolution but create a condition of overload in the half
which was not blocked off. Excessive vibration would re-
sult. Any condition which forces the air to approach the
fan in a non-axial direction should be avoided.
4.5.4 UNEVEN TIP CLEARANCE
Where fan rings are out of round or not centered
with the fan, the tip clearance of each blade will vary as it
makes a revolution. If tip clearance is tight at one point
and excessive at another, proper flow will establish itself
at the tight point, loading the blade to the very tip, while
at the loose point the air will flow from the high pressure
side of the blade through the opening between the blade
tip and the ring and nullify the negative pressure on the
under side of the blade. This will unload the blade near
the tip within the area of excessive tip clearance. Under
this condition, the blade will load and unload near the tip
one or more times per revolution, resulting in an undesir-
able repetitive vibration. Every effort should be made to
keep the tip clearance to a minimum and to have this clear-
ance as constant as possible around the entire ring.
OPERATION