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1999 Clarage

IntrodctionThis document presents ways to avoid the most com-mon fan problems caused by improper storage, installa-tion, operation and maintenance. Installation, operationand maintenance manuals give general instructions onwhat and what not to do. This document will give moredetail as to why these steps are important.

StorageMany fans do not have the chance to operate success-

fully simply due to their treatment and handling duringshipment and storage. Rough handling during shipmentand improper storage can cause damage that is notnoticeable until the fan is in operation. Fans are fre-quently received on site well before they are put intooperation. This often happens on large projects wherethe fan is set in place and then sits idle while the restof the project is completed. Sometimes several monthsgo by before the fan is started. It is discouraging to buy a new fan, only to haveproblems shortly after startup. This can be avoided withproper storage techniques which drastically reduce thelikelihood of having problems. Most problems associated with storage are due tomoisture getting into the bearings. The best way to

avoid moisture problems is to store the fan in a cleanand dry place, preferably indoors. Outdoor storage usu-ally subjects the fan to variations in temperature andhumidity. As the temperature drops, moisture condensesas dew. Condensation in the bearings can cause rustingof internal bearing surfaces, known as puddle corro-sion. If fans cannot be stored in a controlled environment,avoid puddle corrosion by packing the bearings full ofgrease. This eliminates the air pockets where moisturecan condense. Many greases contain rust inhibitors.Adding new grease every month adds more of theseinhibitors. Turn the shaft about ten revolutions whileadding the grease to make sure that all surfaces insidethe bearings are coated. Stop the shaft in a different

location than it was previously stopped at. This way ifany moisture does develop, it will not always be at thesame location. On fan startup the extra grease will purgeout of the bearings. This may make a mess, but it isbetter to deal with a mess than with a bearing failure.With split bearings, the caps can be removed prior tostartup to remove excess grease.

Fan Installation, Operation & MaintenanceHow to Avoid Problems with Yor Fan

Another good idea is to add grease to the outside ofthe bearing seals as this will help seal out moisture. It is not possible to add grease to some small fansand motors that have sealed for life bearings. In thiscase, rotate the shaft monthly. Reduce the belt tension on belt driven fans. Thisreduces the load on the bearings, minimizing the poten-tial for problems. Do not store the fan in a location where it will besubjected to vibration. Vibration may cause internal sur-

faces to rub against each other, damaging the bearings.Damage of this type usually does not cause a problemright away; it may take a couple of months of operationfor it to develop.

Fan FondationsThe structure that supports the fan must be strongenough to support the loads produced by the fan. Manyfan problems are actually structural support problems.The support must be designed to carry both the deadweight of the fan and dynamic loads created while thefan is operating. A well-designed fan support is rigid enough to keepvibration levels low. Before discussing the features of

good fan support design, we need to set up somebackground information on vibration: Vibration is the repetitive motion that results fromforces that vary in amplitude or direction over time. Onecommon cause of vibration is impeller imbalance.Impeller imbalance is a result of the centrifugal forcesacting on an impeller whose center of gravity is offsetslightly from the center of rotation. Not all vibration isbad. Only when the vibration levels exceed certainamplitudes is it a problem. A well-balanced impeller hasits center of gravity close enough to the center of rota-tion that the vibration levels are low. Excessive vibration causes problems in many differentways. It causes lubricant to break down, which allowsmetal to metal contact of bearing surfaces, which then

results in premature bearing failure. It can also causefatigue cracks in the bearings, the bearing supports, orother fan components. It can cause fasteners, such asmotor and bearing hold down bolts or the set screwsthat hold the bearings and impeller to the shaft to workthemselves loose. Many precision processes, such asthe manufacturing of computer chips, cannot toleratehigh levels of vibration. In other installations, soundcaused by vibration can be annoying to the people whomust work nearby.

ENGINEERINGDATA

ED-500Information and Recommendations for the Engineer

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2 Engineering Data 500

Figure 1.

Figure 2.

Vibration Spectrm Plots

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Engineering Data 500

Fan VibrationFigure 1 shows the plot of a vibration spectrum, whichis a plot of vibration amplitude versus frequency. Theseplots are used by vibration technicians to diagnosevibration problems and the general condition of rotatingequipment. The amplitude relates to how loud thevibration is, and the frequency relates to its pitch.Amplitude can be expressed in terms of acceleration,velocity, or displacement, all three of which are relatedmathematically. When dealing with fans, it is convenient

to use cycles per minute for the frequency because itis easier to identify the vibration levels at the fan andmotor speed. Common units for vibration amplitude andfrequency are shown in Table 1.

The spectrum in Figure 1 is for a fan operating at1250 revolutions per minute (rpm = cpm), driven by amotor operating at 1750 rpm. If we were to increase thefan speed, the spike corresponding to the fan speedwould move to the right. If we were to slow it down,the spike would move to the left. Spikes will also be present at the natural frequenciesof the structure. Just as bells or tuning forks have dis-tinct natural frequencies they ring at, structures havenatural frequencies. The fan support in Figure 1 has anatural frequency at 2200 cpm.

ResonanceWhen the fan speed corresponds to the structuresnatural frequency, the fan and structure are in reso-

nance. At resonance, small forces can produce highlevels of vibration. Even a well-balanced fan can producehigh vibration levels at resonance with a structuresnatural frequency. Figure 2 shows what happens whenthe fan speed from Figure 1 is increased to 2200 rpm.As you can see, the vibration level at this frequencyincreases dramatically at resonance. Sometimes thevibration can be lowered by balancing the fan to aneven finer balance, but the fan and structure will be verysensitive. A small amount of dust buildup on the impel-ler, for example, will cause the vibration level to increaseagain. In order to avoid problems with resonance, the sup-port structure for a fan should be designed so that thenatural frequency of the structure is at least 20% high-er than the fan speed. When mounting a fan on an

existing structure, verify that the natural frequency ishigh enough by having a vibration technician perform abump test. A bump test is simply striking the structureand measuring the frequencies at which it rings. If thereis a natural frequency too close to the fan speed,stiffen the structure so that the natural frequencyincreases to the point where it will not be a problem. The best foundation for mounting a fan is a flat, rigidconcrete pad that has a plan area of at least twice theplan area of the fan and is thick enough that the weightof the pad is at least three times the weight of the fan.To keep the edges of the pad from breaking away, theyshould be kept at least six inches from the fan. Thelarge weight of the pad compared to any forces result-

ing from an imbalance of the impeller ensures that thevibration levels will be low. Also, because concrete padsare so rigid, their natural frequencies are usually veryhigh, which avoids resonance problems. Figure 3 shows the best way to anchor a fan to aconcrete pad. T or J bolts provide a strong, rigidconnection to the pad. The pipe sleeve allows for some

flexibility in case the bolt location does not exactlymatch the hole in the fan base. Compression typeanchor bolts are sometimes used, but they can workloose when subjected to loads caused by vibration. Toavoid this problem when using these types of anchors,use as large a size as possible. When the fan is anchored to the pad, level it usingshims. Use 1" to 112" thick shims between the fan baseand the concrete pad. After leveling the fan, build damsaround the pad and fill the gap made by the shims withgrout. Grout is a masonry product, similar to the groutused to set ceramic tile. There are many varieties ofgrout, from mortar types to epoxy types. Epoxy grout,while more expensive, is more durable and more resis-tant to oil and moisture than cementitious grout. After

the grout has set, double check that all of the anchorbolts are tight. Often it is not practical to mount fans on concretepads and they are mounted on structural steel supports.With steel supports it is essential that they be designedfor rotating equipment. It is not only important to con-sider dead loads and natural frequencies, but the sup-port must be rigid enough to keep drive belts or cou-plings aligned. One way to make the design easier is tolocate the fan as close to walls or vertical columns aspossible. Roof mounted fans are a special case ofmounting fans on structural steel supports. The differ-ence is that the steel structure is covered by the roof.The same design criteria must be used. When mounting the fan on a structural steel base

there may be gaps between the fan base and the struc-tural steel base. This occurs because structural steel isnot perfectly flat, and neither are the bases of fans. Fillany gaps with shims before tightening the fan to thesteel base. Since most fan designs have relatively closeclearances between the impeller and fan housing, tight-ening the fan to the base without shims can distort thefan so that the impeller rubs against the housing.

Vibration IsolationThis is a topic that is somewhat controversial in the fanindustry. There are those who advocate a total systemconcept of evaluating a fan and its support system. This

Temporary Form ForGrout Pouring

Hex Nut, Split RingLock Washer, and

Tapered or Flat Washer

1" to 1.5"Grout AllowanceToBe Filled WithNonshrinkingMachinery Grout

Pipe-Bolt SleeveDia. 2 to 21/2Times

Bolt Dia. For Correctionof Alignment Errors

Care Should Be TakenThat Anchor Bolt Sleeves

Are Filled With Grout

J-Bolt Leg Should BeFastened To FoundationRebar

Full Width Stainless

Steel ShimsShimming Surface To BeSmooth, Level, DressedIf Necessary

Leveling Nut, If Used, Should BeBacked Off After Shimming ForFinal Tightening of Hex Nuts

Fan Base Angleor Structural Steel

Figure 3. Concrete Pad Anchor

MEASuREMENT uNITS

Peak-to-Peak Displacement mils (1 mil = .001 in.)

Peak Velocity inches / second (ips)

Acceleration g (1 g = 32.2 ft/sec2)

Frequency Cycles per second (Hz)

Frequency Cycles per minute (cpm)

Table 1. Common Units For Vibration Analysis

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type of analysis looks at the support of a fan impellercomponent by component all the way down to the foot-ings and foundation of the building. Looking at the totalsystem, the structure is designed to avoid resonancewithout the need for vibration isolators. From a technicalpoint of view, this is the correct way to design fan sup-port structures. This concept has been used success-fully on vibration sensitive fan applications such as themanufacturing of computer chips. The other approach is to use vibration isolatorsbetween the fan and the supporting structure. These

isolators, when properly selected, reduce vibration forcestransmitted to the structure by approximately 95%. Thismuch reduction reduces the likelihood of having a reso-nance in the support structure. Depending on the fanspeed, isolators are selected to have a specified amountof deflection when put under load. For example, a springselected to deflect 1" under load on a fan operating at1200 rpm will reduce the forces transmitted to the sup-port by 97%. Various isolator designs, such as metalsprings and rubber-in-shear, are available to accommo-date different loads and speeds. Advocates of total system design point out thatselecting isolators based only on the vertical load is anoversimplification. Fans mounted on isolators not onlymove up and down, but rock back and forth and moveside to side. These additional motions end up increasingthe loads transmitted to the structure, resulting in lessisolation, and can cause problems. On the other hand,vibration isolators work successfully in the majority ofcases.

Figure 4 is a photograph of a fan and motor mount-ed on a structural steel base supported by spring vibra-tion isolators. Like other fan support structures, the basemust be rigid and designed without natural frequenciesnear the fan or motor speeds. Notice the routing of theelectrical conduit to the motor. It is flexible and takesinto account the movement of the motor.Figure 5 shows an inertia base type of vibration base.It is similar to the base in Figure 4, except that the baseis filled with concrete. The weight added by the concrete

creates inertia, reducing the amount of vibration. Theconcrete also makes the base very stiff, making iteasier to design to avoid resonance. The disadvantageof this type of base is that the isolators and the struc-ture supporting the fan and base must be designed tocarry the extra weight of the concrete base.

Figure 6. Well-designed duct configuration

Figure 4. Fan mounted on a structural steel base withspring vibration isolators

Figure 5. Fan mounted on an inertia base

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Dct ConnectionsAny time ductwork is connected to a fan, it is importantto consider any effects the duct may have on fan per-formance. Catalog fan performance is based on uniformflow entering the fan and a straight run of duct on thedischarge. Many duct configurations do not providethese flow conditions and as a result, the fans will notperform at catalog levels. This loss in performance isknown as system effect. Figure 6 shows a well-designed duct configuration that will not have any sys-tem effects, while Figure 7 shows a poorly-designedduct configuration that will lose performance due tosystem effects. For more information on system effectsand methods for estimating their effect on performance,see AMCA Publication 201. Fans mounted on vibration isolators need to haveflexible connections between the fan and the ductwork.Without flexible connections, the ductwork would preventthe movement of the fan on its isolators, reducing theeffectiveness of the isolators. In addition, rigid connec-tions transmit fan vibrations to the duct, opening up thepossibility of exciting resonant frequencies in the duct-

work.It is important to mount flexible inlet duct connections

with the correct amount of slack. Figure 8A shows across section of a properly mounted flexible connection.There is just enough slack in the connection to allowmovement between the fan and ductwork. Figure 8Bshows an improperly mounted connection, with anexcessive amount of slack. Because of the negativepressure at the inlet, the extra material is sucked in. This

Figure 7. Poorly-designed duct configuration

Figure 8A.

Correct Installation

Incorrect Installation

creates an obstruction at the fan inlet and results in asystem effect on fan performance. On some fan designs,this obstruction also causes an increase in the soundlevels produced by the fan. Increases as high as 20dbin the blade pass frequency have been observed. In some cases fans rigidly mounted to their supportsneed flexible duct connections. Fans handling high tem-perature air need to have flexible connections in orderto absorb the thermal expansion of the ductwork. Theends of large plenums can deflect due to pressure load-ing. Ductwork connecting plenums to fans needs to have

flexible connections to prevent the transmission of thesedeflections to the fan. In both of these cases, flexibleconnections allow room for duct movement withoutdamaging the fan. Be careful when using a fan to support ductwork, orwhen using ductwork to support a fan. Most fans arenot designed to carry these external loads, and addingthem to the fan may cause the impeller to rub or causeother misalignments which could damage the fan. Checkwith the fan manufacturer before mounting the fan orductwork this way to make sure the fan design canhandle the loads.

Fan StartpFigure 9 is a typical pre-startup checklist. Before starting

a fan go through the checklist to make sure the fan isready to run. Pay particular attention to safety. Be sureto lock off electrical power before working on any fan.Do not assume that because the factory tightened thefasteners and aligned the belt drives or couplings at the

Verify that proper safety precations have been fol-lowed:

MElectrical power must be locked offCheck fan mechanism components:MNuts, bolts, and setscrews are tight.M System connections are properly made and tight-

ened.MBearings are properly lubricated.MWheel, drives, and fan surfaces are clean and free

of debris.MRotating assembly turns freely and does not rub.MDrives are on correct shafts, properly aligned, and

properly tensioned.Check fan electrical components:MMotor is wired for proper supply voltage.MMotor was properly sized for power and rotational

inertia of the rotating assembly.MMotor is properly grounded.MAll leads are properly insulated.Trial bmpMTurn on power just long enough to start assembly

rotating.MCheck rotation for agreement with the rotationarrow. Does the assembly make any unusual noise?

Correct any problems which may have been fond.(Follow safety gidelines. Make sre electricalpower to the fan is locked off.) Perform checklistagain ntil the fan is operating properly.

Rn p to speed:MAre bearing temperatures acceptable (

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For belt driven fans, proper belt alignment is criticalfor long belt life. Misaligned sheaves cause uneven beltwear and additional flexing of the belt, both of whichreduce the life of the belt. Figure 10 shows properlyaligned sheaves, sheaves with offset misalignment, andsheaves with two types of angular misalignment. Thediagram also shows a straightedge laid across thesheaves. With properly aligned sheaves, the straightedgecontacts the entire face of both sheaves.

Proper belt tension is also important for long belt life.Too much tension puts excessive loads on the belts andthe bearings, reducing the lives of both components. Notenough tension allows belt slippage which generatesheat and drastically reduces the life of the belt.

Belt tensioning gauges, such as the one shown inFigure 11, can be used to determine whether the beltsare tensioned properly. A chart that comes with thegauge specifies a range of force required to deflect thebelts a given amount based on the center distance ofthe sheaves and the belt cross section. The belts areproperly tensioned when the force required to deflect thebelt the specified amount falls within this range. If a belt tensioning gauge is not available, re-tensionthe belts just tight enough so that they do not squealwhen starting the fan. A short chirp is acceptable; asqueal lasting several seconds or longer is not. Before starting the fan after tensioning the belts,

recheck the alignment and realign the sheaves if neces-sary. New belts may stretch a little at first, so recheckbelt tension after a few days of operation.

Bearing LbricationInadequate bearing lubrication is the most commoncause of fan problems. Lubrication is inadequate if thereis not enough lubricant, too infrequent relubrication, orrelubrication with the wrong type of lubricant. Most fansship from the factory with a lubrication label similar tothe one in Figure 12. These labels usually specify theamount of lubricant to add at an interval based on the

bearing size and speed. This interval will be appropriatefor most installations, but in some cases it will be nec-essary to adjust the relubrication interval. The factorsthat affect the relubrication interval are bearing size,speed, the ambient temperature around the bearings, thefan airstream temperature, how wet, dirty or corrosivethe operating conditions are, and the shaft orientation.With installations that are wet, dirty, or corrosive, it isnecessary to add new grease more frequently. Thisflushes contaminants out of the bearings before theywork their way into the rolling portion of the bearing.

High temperatures tend to break down the lubricants, sothey require more frequent replenishment. Bearings withsurface temperatures over 150F may need special hightemperature duty grease. It is much easier for the greaseto leak out of the seals of bearings mounted on verticalshafts, so they need relubrication about twice as oftenas horizontal shaft applications. The best way to determine the relubrication frequen-cy is to inspect the condition of the old grease thatpurges from the seals when adding new grease. If thepurged grease looks just like the new grease, you cango a longer time between relubrications. If the purgedgrease is much darker than the new grease, this indi-cates that the grease is oxidized and you must relubri-cate more frequently. There are many types of grease on the market,manufactured from various bases. Lithium-based greasesare the most common. Be careful when mixing greasesof different bases. For example, mixing a calcium-basedgrease with a lithium-based grease will create a mixturethat hardens and does not provide adequate lubrication.Before using or adding a grease with a different base,

factory that they still will be tight and/or aligned whenstarting the fan at the jobsite. Fasteners can loosen dur-ing shipment and handling, and parts can move out ofalignment.

Figure 11. Belt tensioning

SPAN

FORCE

BELTDEFLECTION

Figure 12. Spherical Roller Bearing Relubrication Schedule

WARNING 1. This eqipment mst not be operated withot proper garding of all moving

parts. While performing maintenance be sre remote power switches arelocked off. See AMCA Pblication 410 for recommended safety practices.

2. Before starting: Check all set screws for tightness, and rotate wheel by hand

to make sre it has not moved in transit.

RELuBRICATION SCHEDuLE (MONTHS)*SPHERICAL ROLLER BEARINGS (SPLIT) PILLOW BLOCKS

SPEED (RPM) 500 700 1000 1500 2000 2500 3000 3500 4000 Grease To Be

SHAFT DIAMETER

Added At

Each Interval

1716" thru 11516" 6 412 4 4 312212212 1 1 0.50 Oz.

2316" thru 21116" 5 412 4 212212112 12 14 14 0.75 Oz.

21516" thru 31516" 412 4 312212112 1 12 2.00 Oz.

4716" thru 41516" 4 4 212 1 12 4.00 Oz.

5716" thru 51516" 4 212112 1 7. 00 Oz.

*Sggested initial greasing interval remove bearing cap and observe conditionof sed grease after lbricating. Adjst lbrication freqency as needed. Hors of

operation, temperatre, and srronding conditions will affect the relbricationfreqency reqired. Clean and repack bearings annally. Remove old grease, pack

bearing fll and fill hosing reservoirs on both sides of bearing to bottom of

shaft.

1. Lbricate with a mltiprpose roller bearing NLGI grade 2 having rst inhibi-tors, and antioxidant additives, and a minimm oil viscosity of 500 SuS at

100F. Some greases having these properties are:

Shell Alvania No. 2 Texaco Premim RB2 Mobil Mobilith SHC 100 Amoco Rykon Premim 2

2. Lbricate bearings prior to extended shtdown or storage and rotate shaftmonthly to aid corrosion protection.

STATIC OIL LuBRICATION

1. use only highest qality mineral oil with a minimm viscosity of 100 SuS at the

oils operation temperatre. The oils operating temperatre is approximately10 greater than the bearings hosing. SAE vales having this viscosity at the

following operating temperatres are: 150F SAE 20; 160F SAE 30; 180F

SAE 40.2. Static oil level shold be at the center of the lowermost roller (do not overfill).

3. Complete lbricant change shold be made annally.

Proper Offset Pigeon- Angle Toed

Figure 10. Sheave & belt alignment(s)

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the old grease must be cleaned from the bearings. Becareful of very high temperature greases. The bondbetween the oil and the thickener may be so great thatthe oil wont release at operating temperature. The bear-ing runs dry despite being apparently filled withgrease. As a fan operates over a period of time, it is notunusual for vibration levels to gradually increase. Thiscan be due to wear, buildup of foreign material on therotating parts, or other effects. Fan operation is muchmore reliable when using periodic vibration readings to

monitor vibration levels and by taking corrective actionsbefore the vibrations get too high. It is possible to use vibration spectra as part of apredictive maintenance program to detect wear in bear-ings. By analyzing spectra taken at regular intervals it ispossible to predict when a bearing will fail. Correctiveaction can then be taken at a scheduled shutdowninstead of at an unscheduled breakdown. AMCA Standard 204-94 contains industry acceptedcriteria for determining at which point vibration levels aretoo high. This standard categorizes fans based on appli-cation and horsepower. The categories range from BV-1,for small, low horsepower residential fans to BV-5 forcritical vibration-sensitive applications such as computerchip manufacturing. Most industrial fans fall into theBV-3 or BV-4 category.

Once the fan application category is determined, thestandard gives startup, alarm and shutdown vibrationlimits. According to the standard, for BV-3 category fans

rigidly mounted, the startup overall vibration levelsshould be below 0.25 inches per second (ips), the alarmlevel is 0.4 ips, and the shutdown level is 0.50 ips. Oncethe vibration levels reach the alarm level, determine thecause of the high levels and schedule corrective actionfor the next shutdown. Monitor the vibration levelsclosely. If the levels reach the shutdown level, take cor-rective action immediately. Continued operation maycause permanent damage to fan components and aneventual catastrophic failure. Overall vibration levels include the vibration at all

frequencies. Upon reaching a high level of vibration, avibration spectrum is a useful tool in determining whatcomponent of the fan is causing the problem. Followingare items to check:Check the background vibration levels (the vibration

may not be coming from the fan). Review the pre-startup checklist.Clean the impeller. Check for worn motor, bearings, belts, or sheaves. Check the fan foundation for looseness or cracks. Perform a trim balance.

ConclsionBy following proper storage, installation, operation and

maintenance guidelines, the majority of fan problems canbe avoided, minimizing downtime and maximizing the lifeand efficiency of the fan.

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