Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

510 Centrifugal Pumps: Design and Application
By marking float extremities and float center on the shaft of the uncoupled
motor, then coupling it and applying thrust in both directions while
rotating on the oil film, it becomes easy to see whether our objectives
have been met. If they have not, the solution becomes fairly obvious—
move the coupling in or out on the shaft, move the motor frame in or out,
add thrust buttons of necessary thickness, or a combination of these.
Bracket Sag Check. In most cases, particularly with spacer couplings, a
sag check should be made on the indicator bracket to be used for the alignment.
In doing this, rim sag should always be checked. Face sag, if face
readings are to be taken, is usually negligible and can be ignored. An exception
could occur with a long dogleg face mount. Procedures for handling this
are shown in Murray [6], but will not be repeated here because this situation
does not arise often with pumps. For vertical pumps, bracket sag may be
ignored. It may exist, but it is constant everywhere and does not require
correction. Vertical pumps seldom require field alignment because they normally
achieve their alignment by machined fits.
To do a rim sag check, mount the bracket on a stiff pipe, zero the indicator
at mid range in the top position, and roll the pipe from top to bottom
on sawhorses, and note the bottom reading. This is "total sag," which is
twice the bracket sag. Do this several times and "jog" or depress the indicator
contact point and let it reseat at top and bottom reading.
To keep less than 0.001 in. error due to calibration pipe sag, using
Schedule 40 calibration pipe, keep the following span limits:
Pipe
Span Between Supports
2 in. 2 ft. 6 in.
3 in. 3 ft.
4 in. 3 ft, 6 in.
6 in. 4 ft. 4 in.
For a face mounted bracket, do the same type of check between lathe
centers or mount inside a pipe capped at one end. The latter method will
usually require a sign reversal, but the numbers will be correct.
Measurement of Linear and Face Dimensions. This should be done to
the nearest Vs in. for small machines and the nearest l fa in. for large machines,
and the dimensions entered into a prepared alignment data form.
Examples of such forms can be found in Murray [6]. Measurements
should be based on indicator contact point centers and foot support centers.