Page 149 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Advanced Machine Alignment

An alternate method would be to measure the temperature of
each supporting leg of both pieces of equipment, while the unit is
operating at normal conditions. It is suggested that the tempera-
ture be taken every two inches from the base plate to the
machine’s shaft center line and the average temperature calcu-
lated for each foot location. This is due to the fact that most equip-
ment supports are not of uniform thickness from their top to their
bottom, and the fact that some heat is being dissipated along their
length. These average temperatures along with the height from
the base plate to the machine’s centerline can be used to calculate
the amount of anticipated thermal growth.
Even though this method is fairly accurate, it still is quite
involved. Even using the manufacturer’s offsets may not be as
accurate as using the hot readings from the actual machine. Your
equipment operates in a unique environment and under unique
conditions. It’s better to measure the actual growth rather than
relying on the equipment manufacturer’s estimated values.

Example 8-3
An electric motor is used to drive a chilled water pump. The
pump was selected as the stationary piece of equipment. With the
unit at normal operating conditions, temperature measurements
were taken on the pump support legs and frame for thermal
growth considerations. The ambient temperature during align-
ment was recorded at 78 degrees, and the unit had been down
long enough to cool to room temperature. The following measure-
ments were recorded:

Machine distances:
A = 12"; B = 16"; C = 36"; D = 14"; E = 56";
Pump Inboard leg height = 17";
Pump Outboard Leg height = 22"

Pump average temperatures (running) previously recorded:
Inboard = 106°F;
Outboard = 138°F;