Page 122 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Rotating Machinery: Practical Solutions

In addition, methods for compensating for thermal growth,
and for checking and correcting running alignment will be dis-
cussed. This will assure the equipment is precisely aligned once it
has stabilized at operating temperatures.

OVERVIEW

Misalignment of two machine shafts can be parallel offset,
angular, or a combination of both. In addition, the misalignment
can be in the horizontal plane, the vertical plane, or both planes.
Generally, most situations will be a combination of all the above.
However, when the problem is attacked one step at a time, the
solution is relatively simple.
Regardless of the method of alignment to be employed, it is
important to examine the equipment to determine which machine
will remain stationary, and which machine(s) will be moved. This
selection is often influenced by such things as connected piping or
fan blades, which must remain, centered in a shroud. In general,
the driver is usually the adjustable piece of equipment, since it
generally has less constraints attached, such as piping. Once the
stationary piece of equipment has been identified, several impor-
tant checks must be performed to assure a proper alignment.
First, pumps and compressors, especially those with a main-
tenance history of bearing or seal problems, should have their
piping taken loose to assure it is not in a strain. If it requires ex-
cessive force to re-connect, piping modifications should be consid-
ered. Here is another example for the need to keep and maintain
informative maintenance records. Once the piping has been in-
spected, there will be no need to recheck its alignment unless
some system changes are made. Later, it will become obvious that
other information about the alignment will be beneficial in future
alignment attempts.
Fans should be inspected to assure they are centered within
their shrouds. Aerodynamic forces resulting from improper cen-
tering can lead to excessive vibrations and premature component
failure. In addition, all blades should be inspected for buildup of