Page 194 - Machinery Component Maintenance

176 Machinery Component Maintenance and Repair

gap difference and centerline offset. This ignores the resulting accuracy
variation due to face diameter and spacer length differences, but works
adequately for many machines.
Be cautious in using alignment tolerances given by coupling manufac-
turers. These are sometimes rather liberal and, while perhaps true for the
coupling itself, may be excessive for the coupled machinery.
A better guideline is illustrated in Figure 5-2, which shows an upper,
absolute misalignment limit, and a lower, “don’t exceed for good long-
term operation limit.” The real criterion is the running vibration. If ex-
cessive, particularly at twice running frequency and axially, further
alignment improvement is probably required. Analysis of failed compo-
nents such as bearings, couplings, and seals can also indicate the need for
improved alignment.

h
Y
E

1 2 345 7 10 20 30 50 100
DISTANCE (INCHES) BETWEEN FLEXURE PLANES

figure 5-2. Misalignment tolerances.