Handbook Of Shaft Alignment Episode 3 Part 5 potx

Figure 21.49 shows a motor-driven fan, where the fan shaft and wheel are supported onpedestals that are separated from the fan housing itself.. shroud at both the inboard and outboard en

FIGURE 21.37 Remove the motor.

FIGURE 21.38 Measure the eccentricity at the lower end of the pump shaft

the measurements as shown in Figure 21.41 and Figure 21.42 Ideally the runout shouldadhere to the guidelines discussed in Chapter 5.

4 Determine if the pump flange face is centered and perpendicular to the pump shaft asshown in Figure 21.43 through Figure 21.45 Since the mating flange faces are oftenrabbeted fits, the rabbet surface is used to check for concentricity and the flange facesurface is used for perpendicularity checks

21.1.6.1 Additional Information on Vertically Mounted Centrifugal Pumps

When the motor and pump are bolted together, they effectively become one contiguous frameand OL2R machinery movement has very little effect on the alignment of the shafts Sincethe entire drive system is typically attached to a floor or the structure of the building,checks should be made to insure that the motor–pump assembly is firmly attached to thefloor via the anchor bolts Leakage at the packing gland and frequent replacements ofthe mechanical seal are indications that a misalignment condition or excessive runoutmay be the culprit Excessive vibration can often be attributed to unbalance conditions inthe motor armature or pump shafts but can also be traced to excessive runout conditions in therotating assembly

FIGURE 21.39 Measure the eccentricity at the upper end of the pump shaft

21.1.7 BLOWERS ANDFANS

There are several different designs of fans and blowers and again, it would be difficult to coverevery aspect of these types of machines Similar to pumps, their purpose is basically to movelarge volumes of a compressible fluid at low pressures from point A to point B A large majority

of smaller horsepower (5 to 200 hp) units are belt-driven as shown in Figure 21.46 Larger unitsare more frequently direct-driven as shown in Figure 21.47 and Figure 21.48 Again, thetemperature of the gas that is conveyed has a great effect on the OL2R conditions of the fan

As discussed in Chapter 5, the ductwork attached to the fan can have a dous influence on obtaining and maintaining accurate alignment, so that many people are

tremen-Total indicated runout (TIR)

0 N

S

E − 2 W

0

N

S

E W 0

N

S

E W 0

S

E W

unwilling to even try to reposition fans and blowers and henceforth declare them the

‘‘stationary’’ machine when aligning them In some situations, where the fan blades are centermounted on the shaft and the shaft is supported by bearings at each end, the position ofthe shaft is dictated by the positions of the bearing pedestals that are not directly attached

to the fan housing The fear in altering the position of the fan bearings is that internal fanblade to shroud clearances could be upset and rubs could occur Here again, the graphing ormodeling technique can be used not only to align the shafts, but also to position the fanhousing to properly set fan blade to shroud clearances

FIGURE 21.41 Split collar and bearing

FIGURE 21.42 Bracket attached to outer race of rolling element bearing held in place with the split collar

Figure 21.49 shows a motor-driven fan, where the fan shaft and wheel are supported onpedestals that are separated from the fan housing itself It is possible for the centerline of thefan housing not to be collinear with the centerline of rotation of the fan shaft To determinewhere the center of the fan housing is, take gap measurements between the fan wheel andthe shroud at the top, bottom, and both sides at the inboard and outboard ends For example,top and bottom gap measurements were taken between the fan wheel and the stationary

FIGURE 21.43 Checking for concentricity on the rabbeted surface

FIGURE 21.44 Checking for perpendicularity on the flange surface

Pump mating flange face and rabbeted fit runout

N

S

E W

of male rabbet

0

FIGURE 21.45 Concentricity and perpendicularity measurements on pump

shroud at both the inboard and outboard ends as shown in Figure 21.49 Notice that the gap

at the twelve o’clock position at the inboard end is 30 mils and at the six o’clock position thegap is 270 mils By adding these two gaps together, the total gap is 300 mils For the fan wheel

to be centered in the up and down direction, there should be a gap of 150 mils at both thetwelve- and six o’clock positions Since the gap is greater at the six o’clock position (270 mils),the housing is 120 mils low at that point with respect to the fan shaft and wheel Likewise theoutboard end is 40 mils too low

FIGURE 21.46 Belt-driven fan

FIGURE 21.47 Direct-driven fan

Figure 21.50 shows the side view of the motor shaft, the fan shaft, and the centerline ofthe bore of the fan housing Assuming that there are no shims under any of the motor, fanbearings, or fan housing bolts, the overlay line could be projected to pivot at the outboardend of the motor and the outboard bearing of the fan and shims can be added under theinboard end of the motor, the inboard bearing of the fan, and the inboard and outboardfoot bolts of the fan housing as shown in Figure 21.50 A similar alignment model can begenerated in top view showing the lateral positions of the motor shaft, the fan shaft, and thecenterline of the bore of the fan housing to achieve correct lateral alignment Once again,the alignment modeling method gives us the opportunity to add as many pieces of infor-mation about our drive system as necessary to enable us to align all the componentsregardless of its complexity.

Typical OL2R movement range of blowers and fans:

Vertical movement: 0 to 80þ mils upward typically asymmetrical (i.e., inboard and outboard

ends do not move up the same amount)

Lateral (sideways) movement: 0 to 20þ mils

Axial movement: 0 to 50þ mils

21.1.7.1 Additional Information on Horizontally Mounted Blowers and Fans

Moderate to excessive off-line soft foot conditions have been experienced on virtually everytype of fan and blower regardless of frame construction design Frequently, the fan bearingsare bolted to the fan frame or to a pedestal, which may also have a soft foot condition Bear inmind that the axial movement amounts mentioned above are for the casing or housing Theshaft may expand more than that and may influence how you should set the off-line shaft end

to shaft end distances For belt-driven fans, excessive vibration is often traceable to excessiveface or rim runout in sheaves Slow increases of vibration on fans often occur due to a dirtbuildup on the fan wheel or uneven erosion or corrosion of the fan wheel Since access to thefan wheel is usually accessible in the field, balancing of fans is frequently done in situ Makesure the alignment and runout are acceptable and that any dirt buildup on the fan wheel hasbeen removed before balancing Balancing is the last thing I do There is nothing morefrustrating than attempting to ‘‘balance out’’ an alignment or runout problem

FIGURE 21.48 Aligning a direct-driven fan

21.1.8 COMPRESSORS

The variation in compressor design is as diverse as pumps and fans Figure 21.51 shows asmall biogas compressor Figure 21.52 shows a multistage horizontally split compressor withthe upper casing removed Figure 21.53 shows a multistage bullgear-driven compressor.Figure 21.54 shows axial flow compressors Figure 21.55 shows a V-shaped two-stage recipro-cating compressor Figure 21.56 shows a chiller compressor In the refining and chemicalindustries, it is not uncommon for several compressors to be driven by a single steam orgas turbine

When gases are compressed, heat is generated and thereby casing expansion cally occurs On multistage compressors such as the ones shown in Figures 21.51 through

Even gap = 0.150 in.

Fan wheel to shroud gap measurement points Fan housing foot bolts

Fan bearing bolting points

Up Side view

Scale: 20 in 50 mils

B E

0 T

B E

0 T Near indicator

+10

− 36 +16

Sag compensated readings

Pivot

Pivot

Raise 70 mils up

at inboard bearing Raise 180 mils up

at inboard fan housing bolts

Raise 55 mils up

at outboard fan housing bolts

FIGURE 21.50 Side view of motor shaft, fan shaft, and fan housing bore

FIGURE 21.51 Small biogas compressor

Figure 21.54, since the compressible fluid is entering the compressor at a much lowertemperature than the discharged gas temperature, uneven OL2R movement frequentlyoccurs Depending on how the suction and discharge piping is attached to the compressorcase, lateral (sideways) OL2R movement can occur as the attached piping expands orcontracts Refrigeration compressors can move downward during operation.

Typical OL2R movement range of compressors:

inboard and outboard ends do not move up the same amount)

Lateral (sideways) movement: 0 to 30þ mils (usually much less than the vertical movement

but can be greater than vertical movement in certain applications)

FIGURE 21.52 Multistage horizontally split compressor

FIGURE 21.53 Multistage bullgear-driven compressor

21.1.8.1 Additional Information on Compressors

Moderate to excessive off-line soft foot conditions have been experienced on virtually everytype of compressor regardless of frame construction design On medium to large compressors,the main lube oil pump is often driven off the compressor or driver shaft where misalignmenthas been observed between the pump and the shaft it is connected to despite the fact that thecompressor and driver shaft may be aligned properly During operation, if there is a backflow(i.e., stall or surge), the compressor shaft may make a rapid movement in the axial direction

If disk or diaphragm couplings are installed, damage could occur to the coupling due to thisviolent axial movement Bear in mind that the axial movement amounts for OL2R conditions

FIGURE 21.54 Axial flow compressors

FIGURE 21.55 Two-stage reciprocating compressor

mentioned above are for the casing or housing The shaft may expand more than that andmay influence how you should set the off-line shaft end to shaft end distances.

21.1.9 HORIZONTALLY MOUNTED ELECTRIC GENERATORS

It is difficult to imagine what our world would be like without electricity Minor poweroutages due to severe weather conditions can make life seem unbearable and power com-panies scramble to get us back on line as quickly as possible so we can get back to ‘‘normal.’’The vast majority of people have no idea what it takes to generate and deliver uninterruptedpower to the grid It is projected that California alone will increase their need for electricity at

a staggering 1000 MW=year Where will it come from? Mostly it will come from rotatingelectric generators driven by steam or gas turbines as shown in Figure 21.57

FIGURE 21.56 Chiller compressor

FIGURE 21.57 Typical alternating current electric generator

Both alternating (AC) and direct (DC) current generators are used in a variety of tries For base load AC electric generating stations, the generators are frequently driven byhigh-, intermediate-, or low-pressure steam turbines and are usually set on a catenary curve(refer to Figure 9.12) Smaller generators may be driven by a single steam turbine Standby,

indus-AC generators are frequently driven by diesel engines at hospitals or industrial plant sites inthe event of a power interruption DC generators are typically driven by an electric motor.Several DC generators can be coupled together, referred to as motor–generator (MG) sets, asshown in Figure 21.58 Electric generators (similar to their cousins—the electric motors) areperhaps the best behaved types of rotating machinery as far as OL2R machinery movement isconcerned As with motors, the maximum recommended rotor to stator air gap eccentricitydifferential is +10% of the total air gap

Where generator armatures are supported in one bearing as found in MG sets, correcting anyair gap clearance problems can also be taken into account when aligning the machinery casings.For a quick review, examine Figure 11.9 that covers the 16-point alignment method Asmentioned in Chapter 11, some drive systems are supported in three bearings On MG sets, themotor armature is supported in two bearings, the generator armature is supported withone bearing, and the armatures are connected together with a spigot fit rigid coupling A similararrangement is often found between an AC generator and its exciter in the electric powerindustry Remember what I have said about attempting to align an engaged rigid coupling?Don’t try it

Figure 21.59 shows a three bearing drive system Rather than use the 16-point methodwhich requires the rigid coupling to be disengaged just enough to provide a gap at thecoupling flange faces while still engaged in the spigot or rabbet fit, another method is toprovide a temporary support at the inboard end of the generator armature as shown inFigure 21.59 With the temporary support in place, the coupling can be completely disen-gaged and both armatures can be rotated Now, the system you choose, the reverse indicator,face–rim, double radial, or a laser–detector system, could be used to capture the shaft-to-shaftmeasurements Remember, the positions of the shafts are dictated by the positions ofthe bearing pedestals and the air gap clearances between the armatures and stator windingsare dictated by the positions of the machine casings which in this case are independent of thebearing pedestals In addition to the shaft-to-shaft alignment readings, air gap clearancesneed to be taken at both ends of both machines

The alignment modeling technique for this drive system is similar to what was discussed inthis chapter on fans as shown in Figure 21.49 and Figure 21.50 In this case, rather thanfinding the location of the bore of the fan housing, air gap measurements are taken betweenthe armature and stator at both ends of both machines to determine the centerline of the bore

FIGURE 21.58 Typical motor–DC generator set

of the stator windings as shown in Figure 21.60 Assuming there are no shims under eitherstator and all three bearing pedestals, the overlay line in Figure 21.60 illustrates one possiblealignment solution Again, the alignment model can be used not only to align the shafts, butalso to center the armature in the stator bore Could you generate the top view alignmentmodel from this information?

Typical OL2R movement range of horizontally mounted electric generators:

typically symmetrical (i.e., inboard and outboard ends move up about the same amount)Lateral (sideways) movement: 0 to 4 mils (usually much less than any vertical movement)Axial movement: 5 to 40þ mils

Up Side view

T

B

0 T

B

0 Motor

+90

–70 +10

Sag compensated readings –60

20 in 10 in 32 in 46 in 18 in.

Temporary bearing support

0.120 in.

0.060 in 0.140 in.

T

B E 0.040 in.

0.080 in 0.120 in.

T

B

E W 0.020 in.

0.190 in.

0.180 in 0.020 in.

W W

FIGURE 21.59 Three bearing drive system

21.1.9.1 Additional Information on Electric Generators

Observed soft foot conditions on generators are the same as for motors Large generators areoften held down with several bolts, necessitating soft foot corrections to be made at everybolting point

When aligning medium to large generators, because the rotors weigh a significant amount,

it is often extremely difficult to rotate them by hand If you decide to use an overhead crane or

Up Side view

+90

− 70 +10

Sag compensate readings

− 60

Generator

Air gap measurements

Centerline of motor stator bore

Raise 45 mils up Raise 80 mils up

0.180 in.

0.090 in 0.110 in.

T

B 0.010 in.

0.190 in.

0.180 in 0.020 in.

FIGURE 21.60 Side view alignment model of the three bearing drive system shown in Figure 21.59