The Balancing Process - Commtest Instruments vbBalancer Instrument Reference Manual

The centrifugal force of a heavy spot on the rotor that causes the
rotor to vibrate increases with the square of the rotational speed. The
vibration level of the rotor may be acceptable at one speed but not at
another. Therefore, it is important to always allow the rotor to settle
to its normal operating speed before taking balancing analysis
measurements.
Whether a rotor should be balanced in one plane or two planes
depends on the dimensions and operating speed of the rotor. The
following guideline is commonly used:
Rotor Length to
Diameter Ratio
0.5 or less
More than 0.5
Note: Before attempting to balance a rotor you must confirm that the
cause of vibration is uneven mass distribution in the rotor. Good
balancing results can be obtained only if vibration is caused by
uneven rotor mass distribution. Attempting to balance a rotor with
other problems will not, in general, reduce the vibration level.

The Balancing Process

A rigid rotor can be balanced in one or two planes. The following
steps are involved:
Setting Balancing Parameters - Select the units and balancing
method.
Initial Reading - Measure the initial imbalance.
Trial Reading - Attach a trial weight to the balancing plane and take
another measurement. For dual plane balancing, the same is also
done for the second plane.
Balancing - Attach correction weights to the balancing plane(s) as
recommended by the instrument.
36 Section 4: Balancing Rotors
Operating Speed
1000 RPM or less
More than 1000 RPM Dual plane balancing
150 RPM or less
More than 150 RPM
Balancing Technique
Single plane balancing
Single plane balancing
Dual plane balancing