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

Vibration and Noise in Pumps 435
procedures. As an example, a model of a piping system analyzed by a
digital acoustic analysis technique is given in Figure 18-5. The system
was for chemical service with three pumps (3000 gpm, 250 psi, 3600
rpm) each 50% capacity (one spare). The predicted frequency response
in the pump system at selected locations is given in Figure 18-6. The natural
frequencies of the energy in the piping system can be compared to
discrete frequencies generated by the pump (i.e., vane passing frequency,
etc). It can immediately be seen that these 3600 rpm pumps (A and B
operating) with a six-vane impeller could cause severe pulsations in the
piping system because its vane passing frequency (6 x 60 rps) matches
an acoustic response at 360 Hz. Based on the acoustic analysis, a sevenvane
impeller should be used that would have its vane passing frequency
at 420 Hz (7 x 60 rps) which has minimal response.
While in the design stage, changing the pump impeller for this system
was a simple solution; however, the primary use of this acoustic analysis
technique is to evaluate alternate piping configurations when the pump
cannot be readily changed as in existing installations. Modifications to
the piping system (i.e., lengths, routing) can be easily simulated to evaluate
the effectiveness in attenuating a particular response mode.
Figure 18-5. Simulation of centrifugal pump piping system.