Page 253 - Machinery Component Maintenance

Machinerj Alignment 235

The following is for " foot-mounted horizontal, end suction centrifugal
pumps driven by electric motors":

For liquids 200°F and below, set motor shaft at same height as pump
shaft.
For liquids above 200"F, set pump shaft .001 in. lower, per 100°F of
temperature above 200°F per in. distance between pump base and shaft
centerline.
Example: 450°F liquid; pump dimension from base to centerline is 10
in.

(450 - 200) (.001)(10) = .025 in. Therefore, set pump .025 in. low
100 (or set motor .025 in. high).

The following applies to "foot mounted pumps or turbines":
(To - Ta)
Thermal growth (mils) = 6 X
100
Where L = Distance from base to shaft centerline, feet
To = Operating temperature, "F
T, = Ambient temperature, "F
For centerline mounted pumps, we are told to change the coefficient
from 6 to 3. Another rule tells us to use the coefficient 3 for foot mounted
pumps!
Yet another source tells us to use the following formula:
(To - Tal L
Thermal growth, inches, = .008 x
3
100 x -9
for centerline mounted pumps.
L
For foot mounted pumps, use L in placc of -.
3
Another rule of thumb says to neglect thermal growth in centerline
mounted pumps when fluid temperature is below 400"F, and to cool the
pedestal when fluid temperature exceeds 400°F. This rule is somewhat
unrealistic, since the benefits of omitting the cooling clearly outweigh the
advantages of including it!
Yet another rule tells us to allow for .0015 in. growth per in. of height
from base to shaft centerline, for any steam turbine-regardless of steam
or ambient temperatures. Another chart goes into elaborate detail, rec-
ommending various differences in centerline height between turbine and
pump based on machine types and service conditions, but without consid-
ering their dimensions.