Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

Vibration and Noise in Pumps 451
Figure 18-16. Eight-stage pump seat geometries and fluid properties.
Table 18-2
Summary of Seal Coefficients
Stiffness
Damping
Principal Cross-Coupled Principal Cross-Coupled
Seal Type K-lb/in K-lb/in C-lb sec/in C-lb sec/in
Neck-Ring 13,400 4900 23 0
Int-Stg Bush -8 370 3 0
Balance Piston -271,000 627,000 25,000 3000
the first mode without altering the mode shape significantly. For an assumed
bearing stiffness of 500,000 lb/in., the first, second, and third
critical speeds from Figure 18-15 are 2570, 7120, and 8830 cpm.
Evaluation of Critical Speed Calculations. To summarize, in the evaluation
of the adequacy of the rotor from the critical speed map and the
mode shapes, the following items should be examined [18]:
• The proximity of the critical speed to running speed or speed range,
The undamped lateral critical speeds should not coincide with the running
speed. Various codes [7] address the allowable margin between
lateral critical speeds and exciting frequencies. To determine if the actual
critical speed will cause excessive vibrations, a rotor response to
unbalance analysis should be performed.