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

Alignment 511
Determination of Tolerances. This is necessary in order to know when
the alignment is adequate and work can be stopped. Murray [6] and
Bloch [1] contain a number of criteria for alignment tolerances based on
coupling and machine type, distance between coupling flex planes, and
rotating speed. Results vary with the different approaches, from very
sloppy to very precise. There is general agreement, however, that coupling
manufacturers' advertised tolerances are too lax for the machines
being coupled, even though they may be all right for the couplings themselves.
A simple rule of thumb that works well for most horizontal
pumps is to allow 0.003 in. maximum centerline offset at measurement
planes and the same amount for maximum face gap difference. For vertical
pumps, in the infrequent cases requiring their manual alignment,
0,00! in. maximum face gap difference is recommended.
Methods of Primary Alignment Measurement
By "primary" measurement, we mean that thermal growth is not determined
thereby, although it may be incorporated into the alignment
data if known from some other source. Table 19-3 compares various primary
alignment measurement methods. Figures 19-3A and B and 19-4
illustrate the two most common methods—face and rim and reverse indicator
(rim and rim).
Table 19-3
Primary Alignment Measurement Methods
Method Advantages Disadvantages
Straightedge, Simple, inexpensive, easy to Less precise than most other
wither use if good coupling rim methods,
without feeler surfaces are available,
gauge Commonly used for
preliminary alignment. Also
used for final alignment of
low speed and/or
intermittently operated
machines.
Tkper gauge; Simple and inexpensive. No Limited application. Does
small hole bracket required. Fairly only part of the alignment
gauge and accurate with care. Used for job.
outside measuring face gaps of
micrometer; close-coupled machines.
inside dial
caliper
(table continued on next page}