Investigation into excessive noise and vibration at sewage pumping station

Challenge
Management at a sewage pumping station in Scotland became increasingly concerned at the excessive noise and vibration levels that occurred within the pumpset, pipework and non-return valve (NRV) infrastructure. These problems caused mounting bracket failures and vibration alarms from the pump casing to go off leading to numerous site visits from management.

Investigations found that the noise and vibration were attributable to a number of factors. With single pumpset operation there was insufficient net positive suction head (NPSH) available to prevent cavitation occurring at high pump operating speeds. This cavitation caused excessive noise and vibration. Resonance of the pumpset, pipework and NRV body was also observed. This appeared to be driven by impeller vane passing frequency effects.

Solution
ESR Technology was contracted to analyse the cause of the excessive pumpset, pipework and NRV vibration and perform on-site investigations as required to support the project. The aim was to propose detail design modifications to alleviate the problems. A key part of the project involved the ESR Technology team supporting the asset maintenance provider in technical discussions with the asset owner and working with both parties to deliver a long term solution.

ESR Technology’s solution included a number of recommendations including:  

  • Modification of the control system so that pump speed during single pump operation was restricted to a maximum of 75% of the maximum operating speed, thereby avoiding cavitation and the associated noise and vibration
  • Modification of the control system to give a ‘soft stop’ during pump changeover to reduce dynamic loads on the NRV
  • Stiffening of the pumpset, pipework and NRV support structures to increase their natural frequencies and thus avoid resonances due to impeller vane passing frequency effects

Benefits
These measures resulted in a significant decrease in the noise and vibration levels of the pumpset, pipework and non-return valve (NRV) equipment. Consequently failures to the mounting brackets was reduced and unnecessary visits to the station resulting from vibration alarms ended.

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