Effective Isolation Treatment Of Vertical Pumps Including Seismic Restraints

Abstract

Three vertical pumps at a wastewater transfer station a few miles away from the San Andreas Fault and next to an apartment building were the source of vibration and noise complaints. To attune the transmitted vibration, a typical isolation system was installed without a significant amount of analysis, and consisted of unrestrained pump base mount pads and flexible couplings on the suction and discharge pipes. Initial testing shows that while the base mount pads worked well, the lack of a positive seismic restraint made those devices unsuitable for use in an earthquake zone. The flexible couplings however actually increased vibration transmitted into the piping because of excessive stiffness. Based on the initial test results and site observations, a new isolation system was required. Although isolation theory is relatively simple, this paper describes how a detailed three-dimensional analytical treatment was required to properly determine the properties of the isolators, including the influence of adequate seismic restraints. Test results are included showing the redesigned system effectively isolates the pumps.