Handbook Of Shaft Alignment Episode 3 Part 5 potx

FIGURE 21.37 Remove the motor.
FIGURE 21.38 Measure the eccentricity at the lower end of the pump shaft.
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690 Shaft Alignment Handbook, Third Edition
the measurements as shown in Figure 21.41 and Figure 21.42. Ideally the runout should
adhere to the guidelines discussed in Chapter 5.
4. Determine if the pump flange face is centered and perpendicular to the pump shaft as
shown in Figure 21.43 through Figure 21.45. Since the mating flange faces are often
rabbeted fits, the rabbet surface is used to check for concentricity and the flange face
surface 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 frame
and OL2R machinery movement has very little effect on the alignment of the shafts. Since
the 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 the
floor via the anchor bolts. Leakage at the packing gland and frequent replacements of
the mechanical seal are indications that a misalignment condition or excessive runout
may be the culprit. Excessive vibration can often be attributed to unbalance conditions in
the motor armature or pump shafts but can also be traced to excessive runout conditions in the
rotating assembly.
FIGURE 21.39 Measure the eccentricity at the upper end of the pump shaft.
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Alignment Considerations for Specific Types of Machinery 691
21.1.7 BLOWERS AND FANS
There are several different designs of fans and blowers and again, it would be difficult to cover
every aspect of these types of machines. Similar to pumps, their purpose is basically to move
large 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 units
are more frequently direct-driven as shown in Figure 21.47 and Figure 21.48. Again, the
temperature 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 tremen-

dous influence on obtaining and maintaining accurate alignment, so that many people are
Total indicated
runout (TIR)
0
N
S
E −2W
0
N
S
EW
0
N
S
EW
0
−2.5
+16.5 +3
+1
+18 +4
+4
−7.5
N
S
EW
0
−0.5 −4
N
S
EW

0
+3 −1
−2.5
View from above when
runout measurements
were taken
N
S
EW
Key
0
50
10
40
20
30
+
_
10
40
20
30
5 in.
6 in.
20 in.
44 in.
11.25 in.
FIGURE 21.40 Eccentricity measurements along the pump shaft and its extension.
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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 center
mounted on the shaft and the shaft is supported by bearings at each end, the position of
the 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 fan
blade to shroud clearances could be upset and rubs could occur. Here again, the graphing or
modeling technique can be used not only to align the shafts, but also to position the fan
housing 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.
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Alignment Considerations for Specific Types of Machinery 693
Figure 21.49 shows a motor-driven fan, where the fan shaft and wheel are supported on
pedestals that are separated from the fan housing itself. It is possible for the centerline of the
fan housing not to be collinear with the centerline of rotation of the fan shaft. To determine
where the center of the fan housing is, take gap measurements between the fan wheel and
the 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.
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Pump mating flange face
and rabbeted fit runout
N
S
EW
0
0
50

10
40
20
30
+
_
10
40
20
30
0
0
0
+9
−10
−4
−1
−2
−4.5
−9.5
−6.5
−3.5
−16
Measurements
on male rabbet
Apparent
centerline of
male rabbet
Centerline of
shaft

Exaggerated
apparent position
of male rabbet
0
FIGURE 21.45 Concentricity and perpendicularity measurements on pump.
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Alignment Considerations for Specific Types of Machinery 695
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 the
gap 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 the
twelve- 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 the
outboard end is 40 mils too low.
FIGURE 21.46 Belt-driven fan.
FIGURE 21.47 Direct-driven fan.
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Figure 21.50 shows the side view of the motor shaft, the fan shaft, and the centerline of
the bore of the fan housing. Assuming that there are no shims under any of the motor, fan
bearings, or fan housing bolts, the overlay line could be projected to pivot at the outboard
end of the motor and the outboard bearing of the fan and shims can be added under the
inboard end of the motor, the inboard bearing of the fan, and the inboard and outboard
foot bolts of the fan housing as shown in Figure 21.50. A similar alignment model can be
generated in top view showing the lateral positions of the motor shaft, the fan shaft, and the
centerline 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 components
regardless of its complexity.
Typical OL2R movement range of blowers and fans:

Vertical movement: 0 to 80þmils 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 every
type of fan and blower regardless of frame construction design. Frequently, the fan bearings
are bolted to the fan frame or to a pedestal, which may also have a soft foot condition. Bear in
mind that the axial movement amounts mentioned above are for the casing or housing. The
shaft 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 excessive
face or rim runout in sheaves. Slow increases of vibration on fans often occur due to a dirt
buildup on the fan wheel or uneven erosion or corrosion of the fan wheel. Since access to the
fan wheel is usually accessible in the field, balancing of fans is frequently done in situ. Make
sure the alignment and runout are acceptable and that any dirt buildup on the fan wheel has
been removed before balancing. Balancing is the last thing I do. There is nothing more
frustrating than attempting to ‘‘balance out’’ an alignment or runout problem.
FIGURE 21.48 Aligning a direct-driven fan.
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21.1.8 COMPRESSORS
The variation in compressor design is as diverse as pumps and fans. Figure 21.51 shows a
small biogas compressor. Figure 21.52 shows a multistage horizontally split compressor with
the 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 chemical
industries, it is not uncommon for several compressors to be driven by a single steam or
gas turbine.
When gases are compressed, heat is generated and thereby casing expansion typi-
cally occurs. On multistage compressors such as the ones shown in Figures 21.51 through

94 in.64 in. 16 in.12 in. 10 in.
Motor
Fan
4 in.
Near indicator
Far indicator
Up
Side view
Scale: 20 in.
Motor Fan
10 in.
10 in.
0.190 in.
0.110 in.
0.030 in.
0.270 in.
4 in.
4 in.
Gaps between fan wheel and shroud
Total gap = 0.300
in.
Even gap = 0.150 in.
Fan wheel to shroud gap
measurement points
Fan housing foot bolts
Fan bearing bolting points
0
50
10
40

20
30
+
_
10
40
20
30
0
50
10
40
20
30
+
_
10
40
20
30
FIGURE 21.49 Motor-driven fan where fan shaft is supported on separate pedestals.
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Up
Side view
Scale: 20 in.
50 mils
B
E
0

T
B
E
0
T
Near indicator
+10
−36+16
Sag
compensated
readings
−20
+24 −14
Far indicator
Motor Fan
Centerline of fan housing
Lower 72 mils
down
Raise 42 mils up
Overlay line
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
WW
FIGURE 21.50 Side view of motor shaft, fan shaft, and fan housing bore.
FIGURE 21.51 Small biogas compressor.
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Alignment Considerations for Specific Types of Machinery 699
Figure 21.54, since the compressible fluid is entering the compressor at a much lower
temperature than the discharged gas temperature, uneven OL2R movement frequently
occurs. Depending on how the suction and discharge piping is attached to the compressor
case, lateral (sideways) OL2R movement can occur as the attached piping expands or
contracts. Refrigeration compressors can move downward during operation.
Typical OL2R movement range of compressors:
Vertical movement:10þ mils downward to 80þ mils upward typically asymmetrical (i.e.,
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)
Axial movement: À10þ to 100þ mils
FIGURE 21.52 Multistage horizontally split compressor.
FIGURE 21.53 Multistage bullgear-driven compressor.
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21.1.8.1 Additional Information on Compressors
Moderate to excessive off-line soft foot conditions have been experienced on virtually every
type 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 misalignment
has been observed between the pump and the shaft it is connected to despite the fact that the
compressor 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 this
violent 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.
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Alignment Considerations for Specific Types of Machinery 701
mentioned above are for the casing or housing. The shaft may expand more than that and
may 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 power
outages 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 uninterrupted
power 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 rotating
electric 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.
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Both alternating (AC) and direct (DC) current generators are used in a variety of indus-
tries. For base load AC electric generating stations, the generators are frequently driven by
high-, 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,
AC generators are frequently driven by diesel engines at hospitals or industrial plant sites in
the 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, as
shown in Figure 21.58. Electric generators (similar to their cousins—the electric motors) are
perhaps the best behaved types of rotating machinery as far as OL2R machinery movement is
concerned. As with motors, the maximum recommended rotor to stator air gap eccentricity
differential is +10% of the total air gap.
Where generator armatures are supported in one bearing as found in MG sets, correcting any

air 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. As
mentioned in Chapter 11, some drive systems are supported in three bearings. On MG sets, the
motor armature is supported in two bearings, the generator armature is supported with
one bearing, and the armatures are connected together with a spigot fit rigid coupling. A similar
arrangement is often found between an AC generator and its exciter in the electric power
industry. 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 method
which requires the rigid coupling to be disengaged just enough to provide a gap at the
coupling flange faces while still engaged in the spigot or rabbet fit, another method is to
provide a temporary support at the inboard end of the generator armature as shown in
Figure 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-shaft
measurements. Remember, the positions of the shafts are dictated by the positions of
the bearing pedestals and the air gap clearances between the armatures and stator windings
are dictated by the positions of the machine casings which in this case are independent of the
bearing pedestals. In addition to the shaft-to-shaft alignment readings, air gap clearances
need to be taken at both ends of both machines.
The alignment modeling technique for this drive system is similar to what was discussed in
this chapter on fans as shown in Figure 21.49 and Figure 21.50. In this case, rather than
finding the location of the bore of the fan housing, air gap measurements are taken between
the armature and stator at both ends of both machines to determine the centerline of the bore
FIGURE 21.58 Typical motor–DC generator set.
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Alignment Considerations for Specific Types of Machinery 703
of the stator windings as shown in Figure 21.60. Assuming there are no shims under either
stator and all three bearing pedestals, the overlay line in Figure 21.60 illustrates one possible
alignment solution. Again, the alignment model can be used not only to align the shafts, but

also to center the armature in the stator bore. Could you generate the top view alignment
model from this information?
Typical OL2R movement range of horizontally mounted electric generators:
Vertical movement: 1 to 5 mils upward (5 to 200 hp); 3 to 30þ mils upward (200þ hp),
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
Motor Generator
24 in. 50 in. 10 in.
Up
Side view
Scale: 20 in. 50 mils
T
B
0
T
B
E
W
EW
0
Motor
+90
–70+10
Sag
compensated
readings
–60
–60 +150
Generator

View looking east
Air gap
measurement point
Air gap
measurement point
Air gap
measurement point
Air gap
measurement point
20 in. 10 in. 32 in. 46 in.
18 in.
Temporary bearing support
0
50
10
40
20
30
+
_
10
40
20
30
0
50
10
40
20
30

+
_
10
40
20
30
0.160 in.
T
B
E
0.080 in.
0.120 in.
0.060 in. 0.140 in.
T
B
E
0.040 in.
0.080 in.
0.120 in.
T
B
EW
0.020 in.
0.180 in.
0.090 in. 0.110 in.
T
B
EW
0.010 in.
0.190 in.

0.180 in. 0.020 in.
W
W
FIGURE 21.59 Three bearing drive system.
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21.1.9.1 Additional Information on Electric Generators
Observed soft foot conditions on generators are the same as for motors. Large generators are
often held down with several bolts, necessitating soft foot corrections to be made at every
bolting 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
Scale:
20 in. 50 mils
Motor
Generator
Centerline of generator stator bore
Raise 80 mils up
Overlay line
Pivot
Pivot
T
B
EW
0
T
B
EW

0
Motor
+90
−70+10
Sag
compensate
readin
g
s
−60
−60 +150
Generator
Air gap measurements
Stator is low by 20 mils Stator is low by 60 mils Stator is low by 80 mils Stator is low by 90 mils
Centerline of motor stator bore
Raise 45 mils up
Raise 80 mils up
Raise 85 mils up
Raise 87 mils up
0.160 in.
T
B
EW E E EWW W
0.080 in.
0.120 in.
0.060 in. 0.140 in.
T
B
0.040 in.
0.080 in.

0.120 in.
T
B
0.020 in.
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.
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Alignment Considerations for Specific Types of Machinery 705
other similar device to aid in rotation, insure that you have made the desired rotation of the
shaft to measure the side or bottom shaft positions, so that you remove the tension on the
crane or chain fall before taking your measurement. Any excessive tension on the lifting and
rotational device may elastically bend the shafts causing erroneous readings.
As mentioned in Chapter 9 and illustrated in Figure 21.61, metal is elastic, shafts are made
out of metal, long metal cylinders supported at both ends will have a tendency to sag in
between the supports. When connecting two shafts together with a rigid coupling, effectively
you are assembling one continuous shaft supported at four points with the capability of
disconnecting them between the middle two bearings. The ideal situation is to insure that each
of the four bearings carries 25% of the entire load (assuming that the rotors are axially
symmetric). Since the shafts are not infinitely stiff as shown in the top drawing in Figure 21.61
then to achieve even loading, it would be most desirable to match the curved centerline of
rotation to the natural curve that occurs on the elastically bending shafts as shown in the
second from the bottom drawing. However, in many instances, I see people aligning rigid
couplings with a larger gap at the bottom than at the top as shown in the bottom drawing in

Figure 21.61. Would this not have a tendency to strain the shafts, slightly unload the inboard
Infinitely stiff shafts with shaft centerlines collinear with support centers
Parabolically curved shafts positioned in supports whose bores are collinear
Parabolically curved shafts positioned in supports whose bores are set on a matching parabola
Parabolically curved shafts positioned in supports whose bores are not set on a matching parabola
FIGURE 21.61 Which alignment condition is correct?
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bearings, and slightly overload the outboard bearings? Of course, the best way to determine
the load on a bearing is to install strain gauges in each bearing right? Where pray tell has this
been done?
On some larger turbine generator drive systems, there may be a long spool piece (often
referred to as a jackshaft) connecting two of the turbines together. One practice is to remove a
set of coupling bolts at one turbine only and perform a 20-point alignment check from the
jackshaft to the turbine. Bear in mind that the overhung weight of the jackshaft will cause the
disengaged end to ‘‘droop’’ a certain amount. The amount of droop is often calculated and
rarely measured. Figure 21.62 shows a method to actually measure cantilevered droop on a
jackshaft to verify the calculated droop.
21.1.10 VERTICALLY MOUNTED ELECTRIC GENERATORS
Vertically oriented electric generators are principally found at hydroelectric generating sta-
tions. The generator is mounted to a floor or building structure and a rigid coupling connects
a water turbine shaft to the lower end of the generator armature as shown in Figure 21.63.
The upper bearing of the generator is both a radial and thrust bearing that supports the
weight of the armature and the water turbine. A lower radial bearing is located above the rigid
0
50
10
40
20
30

+
_
10
40
20
30
0
50
10
40
20
30
+
_
10
40
20
30
Align jackshaft to
shaft with no offset
and no angle here
Temporary supports
Bolt jackshaft to shaft
Dial indicator and magnetic base
Remove temporary supports and
measure droop with indicator
FIGURE 21.62 Measuring droop in a jackshaft.
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Alignment Considerations for Specific Types of Machinery 707
coupling. Another design has a single radial–thrust bearing assembly located below the

generator armature. All designs incorporate one, if not two turbine guide bearings.
In an ideal world, the generator and turbine shaft would be perfectly plumb the thrust
bearing evenly loaded on all of its pads and the centerline of rotation of the generator shaft
would be concentric with the bore of all the radial bearings. In the real world, the thrust
runner may not be perpendicular to the centerline of rotation of the generator shaft; the
Upper radial bearing
Thrust bearing
Lower radial bearing
Rigid coupling
Water turbine
Armature
StatorStator
Turbine guide bearing
FIGURE 21.63 Hydroelectric generator drive system.
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generator and turbine shafts could have excessive radial runout; the coupling hub flange faces
may not be perpendicular to the centerline of rotation of their shafts; the coupling bolt hole
circle could be eccentric; and the radial bearings could be misaligned. There are four major
issues to be dealt with: concentricity, perpendicularity, plumb, and straightness.
With the shafts removed, concentricity of the stationary components with respect to a
vertical plumb line can be measured. Figure 21.64 shows a plumb line made out of stainless
steel, nonmagnetic piano wire suspended from a metal frame above the upper bearing. At the
other end of the piano wire is a finned plumb bob that is suspended in a bucket of viscous oil
(e.g., SAE 90 weight) below the turbine guide bearing to dampen any movement of the wire if
it is touched. The bucket should be sitting on a nonconductive frame (e.g., wood).
At the upper bearing, the plumb wire is translated in the north, south, east, and west
direction so that it is concentric with the top of the upper bearing. To center the wire, an
electric inside micrometer is used to measure the distance from the bore of the bearing to
the suspended wire. The electric micrometer consists of an inside micrometer, headphones,

and a battery as shown in Figure 21.65. One end of the micrometer is anchored against the
bore of the bearing. The micrometer drum is then turned slowly to increase the length of
the micrometer assembly. When the tip of the micrometer touches the wire, current begins
to flow that can be heard in the headphones as a ‘‘click.’’ If the electric micrometer is
continually touching the wire, a ‘‘hissing’’ sound will be heard. If you know that the inside
micrometer is touching the bearing surface and the wire and no noise is heard, you may
not have electrical continuity from the frame to which the piano wire is attached to the
bearing bore. To verify continuity, use a volt–ohm-meter set to measure resistance. Touch
Piano wire plumb line
Concentricity checks made
for bearings, stator, seals, etc.
Finned plumb bob in bucket of oil
FIGURE 21.64 Plumb line positioned for concentricity checks.
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Alignment Considerations for Specific Types of Machinery 709
one lead to the piano wire and the other lead to the bore of the bearing. If you have
continuity (i.e., the capacity for electric current to flow), the resistance will be low (e.g.,
less than 10 ohms). If the resistance is high or at infinity, you may have to run an insulated
wire from the piano wire frame to the bearing (and all other measurement points) to
complete the circuit.
To insure that the micrometer is at a perpendicular angle to the piano wire, it is adjusted
until the inside micrometer is at its shortest length to barely contact the wire. The distance is
then recorded. Three additional measurements are taken at 908 from the initial inside micro-
meter reading and recorded. If all four distances are the same, the wire is centered. If not, the
position of the wire is adjusted from the upper support based on the mathematical average of
the four inside micrometer readings. Once the wire is centered at the top of the upper bearing,
measurements at any point along the length of the wire to a stationary object can then be
measured.
Measurements are then taken at the lower part of the upper bearing, the stator windings,
the upper and lower points on the lower bearing, the upper and lower points on the turbine

guide bearing, and any other critical clearances along the length of the rotating assembly.
Many radial bearings incorporate wedge-shaped segments, so care must be taken when
measuring distances at the bearings to insure that the inside micrometer tip is at the same
point on each wedge. If the bearings have been removed, then the measurements are taken to
the bearing-housing bore. The general rules of thumb for concentricity are as follows:
.
Bearings: 20% of diametral bearing clearance
.
Stator: 5% of design air gap (where stator air gap is +5% of design air gap)
.
Seal ring: 10% of diametral seal ring clearance
If for some reason one or more of the components are not concentric with a plumb centerline,
then you will have to position the device to make it concentric. This could be the upper
0123456789
0
5
AA+
−
FIGURE 21.65 An electric inside micrometer.
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710 Shaft Alignment Handbook, Third Edition
generator bearing, the lower generator bearing, the stator, the turbine guide bearing, the seals,
the upper and lower seal or wear rings of the turbine, etc. An alignment model can be
constructed to show the position of each component (bearings, stator, and seals). You must
then determine which of the components are not concentric, how far and which way they
must be moved, and what you have to do to place them where they need to be. In some cases,
that might be an easy task, in other cases, someplace between a headache and a pure
nightmare. Hopefully the three bearings and all the seals are concentric and only the stator
needs to be repositioned. Once we know that the stationary components are concentric to a
plumb line that represents the desired centerline of rotation, we can now begin our investi-

gation of the rotating assembly itself. There is another way to determine if the stationary
components are concentric with the shafts installed.
Four issues concerning the condition of the rotating assembly need to be measured and
corrected if they are out of tolerance.
1. Is the thrust runner perpendicular to the centerline of the generator shaft?
2. Are both coupling hub flange faces perpendicular to their respective shafts?
3. Are the shafts straight?
4. Is the centerline of rotation out of plumb?
The first three items effectively deal with runout conditions discussed at length in Chapter
5 with ‘‘preliminary’’ as the key word here. Figure 21.66 shows what would happen if the
Thrust runner is not
perpendicular to centerline
of rotation
Conical whirling orbit
is produced with
locus at thrust
runner
Not 908
FIGURE 21.66 (See color insert following page 322.) A nonperpendicular thrust runner face will force
the rotating assembly to orbit.
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Alignment Considerations for Specific Types of Machinery 711
thrust runner is not perpendicular to the shaft with the centerline of rotation plumb.
Figure 21.67 shows what would happen if either or both of the coupling hub flange faces
are not perpendicular to their shafts with the generator shaft plumb. One of our objectives
is to determine if the centerline of rotation of the entire rotating assembly (i.e., the coupled
generator and turbine shafts) is plumb. In other words, if the thrust bearing is not level
and the thrust runner is not perpendicular to the shaft, the rotating assembly would produce
a spinning cone and its centerline of rotation would be pitched at an angle as shown in
Figure 21.68.

If we happen to deal with the condition shown in Figure 21.68, the shafts have stopped
rotating the high spot of the runout, which will stop at some random angular position (e.g.,
southeast). If we then attempt to measure the plumb of the shafts with north, south, east, and
west as our reference points, how do we know how much of what we are measuring at those
908 positions is due to an out of plumb condition and how much is due to a runout condition?
We do not know. We first have to establish how much runout is present before we attempt to
measure any type of alignment condition.
It makes no sense to attempt to align machinery with bent shafts, problems with the
coupling, and problems with one of the components on the rotors (e.g., a thrust runner).
Why do you waste your time in aligning shafts that have problems with them? If you align the
centerlines of rotation and then discover that there is an issue with one or more of the shafts,
all of the effort you spent in aligning is waste of time. Why? Because you may have to replace
Coupling hub
flange face is not
perpendicular to
centerline of
rotation
Conical whirling orbit
is produced with
locus at coupling
flange face
Not 908
FIGURE 21.67 A nonperpendicular coupling hub flange face will force the turbine shaft to orbit.
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712 Shaft Alignment Handbook, Third Edition
a shaft, a coupling hub, a thrust runner, or at least machine with the component to correct
those problems. To do that, you may very well have to disassemble the machines. Once the
problems have been corrected within acceptable criteria, you are back aligning again. Save
yourself some grief, discover and correct these problems before you ever start aligning. If
we check the runout first, then we can not only ascertain if the runout is acceptable, we also

know where the high spots are and can place them at an angular position of our choosing
(e.g., north). Then we know how much of what we are measuring is due to runout and how
Thrust runner is not
perpendicular to centerline
of rotation causing the
conical rotation
Centerline of rotation
is pitched at an angle
because thrust
bearing is not
perfectly level
Perfectly plumb centerline
FIGURE 21.68 Combination of out of plumb centerline of rotation combined with a thrust runner that
is not perpendicular to its centerline of rotation.
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Alignment Considerations for Specific Types of Machinery 713
much is due to an out of plumb condition. If you are not clear on this, you may want to go
back and study Figure 21.20 and Figure 21.27.
The rotor in Figure 21.68 will have a propensity to want to run on a pure vertical plumb
line and the guide bearings would force the shafts to their respective positions but the radial
forces on those bearings would be undesirable and the thrust runner would only be contacting
a few of the thrust shoes on the ‘‘high’’ side of the thrust bearing greatly diminishing its life
span. The whirling cone would produce excessive vibration particularly at the lower generator
bearing and the turbine guide bearing. Although the runout and perpendicularity problems
are exaggerated for clarity as shown in Figure 21.66 through Figure 21.68, you can see that if
the guide bearings were in place, the capacity to accurately measure the position or runout
of the rotor would not be possible. To accurately measure the runout and plumb condition of
the rotor, the upper and lower generator bearings and the turbine guide bearing should be
removed. The entire rotor assembly should only be sitting on the thrust bearing and some-
what centered. The rotor should be free to swing back and forth freely with just a slight

amount of force.
The perpendicularity condition is typically measured by the amount of runout near the
turbine guide bearing rather than as a face runout condition on the thrust runner itself or on
the coupling hub flange faces. The goal is to level the thrust bearing so the center of the cone
of runout is within acceptable limits and still stay within an acceptable cone orbit diameter.
The general rules of thumb are as follows:
.
Radial runout not to exceed 0.003 in. (3 mils) along the entire length of both shafts.
.
Center of the cone of runout (plumb line of runout) is 0.000025 in. times the length of the
shaft measured from the highest to lowest plumb reading. For example, if the distance
from the highest to lowest plumb reading is 100 in., then the maximum recommended out
of plumb deviation of the centerline of rotation would be 0.0025 in.
.
Cone orbit diameter (also known as static runout) is 0.002 in. times the length of the shaft
from the thrust bearing to the runout measured above the turbine guide bearing divided
by the diameter of the thrust runner. For example, if the length of the shaft from the
thrust bearing to the runout measured above the turbine guide bearing is 300 in. and the
diameter of the thrust runner is 30 in., then the maximum static runout should not exceed
20 mils (0.020 in.).
Figure 21.69 shows the setup for measuring the runout using dial indicators. Two indicators,
908 apart should be set up at the upper generator bearing to observe the position of the rotor
as the assembly is rotated to determine if the shaft is sliding laterally on the thrust bearing
surface during rotation. Another indicator is placed just above the turbine guide bearing to
measure the runout at that point. Additional indicators could (and probably should) be
placed at various points along the length of the shafts to aid in discovering possible problems
such as a bent shaft, cocked coupling hub flange faces, eccentric couplings, and a cocked
thrust runner. At least two rotations should be made to verify the consistency of the amount
and angular position of the high spots. You may want to initially set up just the indicator
above the turbine guide bearing. If the runout condition there is excessive, then the additional

indicators should be set up to determine the source of the runout condition.
One technique used to measure the plumbness of the rotating assembly is to install four
plumb lines similar to the arrangement shown in Figure 21.71. The plumb lines are suspended
from a metal frame below the lower generator bearing and spaced 908 apart. It is not
necessary to position each plumb line at exactly the same distance from the shaft. What
you will be measuring is the difference in distance from each plumb line to the shaft at several
points along the length of that plumb wire. Again, an electric inside micrometer will be used to
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