Page 154 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Rotating Machinery: Practical Solutions

Substituting the readings from Example 8-3 into Equations
(8.5) and (8.6) yields plus two mils (+2) for the rim indicator and
zero (0) for the face indicator.
Either method can be employed to achieve good results. In
general, the calculator method is slightly more accurate. The
larger the scale chosen for the graph, the better the accuracy.
However, it is always advisable to work both methods to assure
there is no mistake.
When approaching an alignment problem, break it down into
simple parts. If an equipment train consisted of a steam turbine,
gearbox, centrifugal pump, a second gearbox, and a diesel engine,
the problem is no more complex than a simple pump and electric
motor. Establish the stationary piece of equipment, and then align
the next piece to it. It then becomes the stationary piece of equip-
ment for the subsequent alignment. Continue until all the equip-
ment is aligned. This will work even if the chosen stationary
equipment is in the center of the train of equipment.

EQUIPMENT WITH DRIVESHAFTS

Dealing with equipment with driveshafts, such as aligning a
cooling tower fan, is also a straightforward process. The fixture is
first set up across the coupling from the motor to the drive shaft,
and readings are taken. Next, the fixture is moved and placed on
the drive shaft to read across the coupling to the gearbox. Again
readings are taken.
In the first case, the B and C distances were from the gear box
feet to the rim indicator stem, while it was mounted to the motor
shaft. In the second case, the B1 and C1 distances are from the gear
box feet to the new indicator location. By superimposing these
two graphs, the total correction required is shown. Simply count
or measure the corrections for each foot and add them together.
The result is the actual correction required. Thus, you only need to
make one corrective move for both couplings.
In Figure 8-20, if the first run inboard correction is plus five