Page 155 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Advanced Machine Alignment

A A’
B
C
B’
C’

Run #2
IB IB
F Run #1
OB F
R
R OB

Figure 8-20. Aligning Equipment with Driveshafts

mils (+5) and the second run inboard correction is minus five mils
(–5) the result is zero. Thus the inboard foot is ok. If the first run
outboard correction was plus nine mils (+9) and the second run
outboard corrections is minus one mil (–1), the result is to add
eight mils (+8) to the outboard feet.

U-JOINT COUPLINGS

One word of caution: Some companies have changed to U-
joints in the cooling tower fan drive shafts. Often, maintenance
personnel attribute premature failure of these U-joints to corro-
sion, because after one fails, the needles and cup are filled with
rust. This may be due to improper alignment. A U-joint must be
misaligned a proper amount to assure proper lubrication of the
needle bearings. Too much misalignment will cause large velocity
fluctuations and uses excessive horsepower; too little, and the U-
joint bearings will fail due to a lack of lubrication.