Page 160 - Know and Understand Centrifugal Pumps

Pump and Motor Alignment

Wear and rubbing between close tolerance rotary and stationary
elements in the pump leading to their failure.
Premature driver bearing failure.
Increased energy consumption.
Excessive operating temperatures and lubricant failure.

One of the most important and least considered points of correct
alignment is the relationship with the power transmitted from the
motor to the pump. An almost perfect alignment (0.003 inch) with an
adequate and new coupling transmits almost 100% of the motor’s
power (there will always be some small losses). The Pump performance
curve identifies the BHP or brake horsepower required for the pump to
perform at its duty point.
The next graph (Figure 10-1) indicates the expected continuous
running time of rotating equipment with increasing misalignment. As
you soon see, the alignment improves and so does the service time.

ROTATING MACHlN ERY FA1 LU RE TIM E
DUE TO MISALIGNMENT
1000.0

z
0 100.0
F
2
W
n
0
U
0 10.0
v)
I
I-
z
0
I
5 1.0
0
3
-
E
Z
0
0
0.1
0.002 0.050 0.050 0.100
TOTAL MISALIGNMENT IN INCHES

Fiaure 10-1

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