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Power Generation
Liquid Ring Vacuum Pump
Change in operational philosophy to reduce failures of pumps

Vacuum Pump Failure Investigation

Failure Investigation of Liquid Ring Vacuum pump with operational philosophy modifications.

The Project

Under one of our Long Term Service Agreements we have the responsibility for the Steam Turbine – Generator, ACC and associated equipment, including the liquid ring vacuum pumps.

Our client experienced a critical failure during the start up of the plant which required replacement of one of the operational liquid ring vacuum pumps.  We investigated the issue to ensure that a similar failure would not occur again.


We performed a Root Cause Analysis of the failed pump, investigating the conditions during operation and assessed for potential mechanical failure.

Our experience with liquid ring pumps identified that the most common cause of failure relates to loss of sealing water during operation.  Due to the risk of cavitation within these pumps, a controlled temperature supply of sealing water must be available to prevent critical damage.

Upon inspection of the damaged pump we identified that the liquid ring impeller had welded itself against the pump end plate where the clearance was at its lowest.  This identified that cooling flow was insufficient during the event.

From assessing the control system, we understood that there was no protection from the loss of sealing water, and under certain circumstances the pumps could be operational with an unacceptably low level in the sealing water tank.

From our analysis we worked with the plant controls engineers to adapt the system to ensure that the liquid ring vacuum pumps could not be made operational without an adequate sealing water level being present.

We ensured that a solution was found quickly to prevent a similar failure occurring again.  The solution was aimed at preventing any mechanical modifications to the system which would have required the plant to be shutdown.

We worked closely with plant operators and mechanical teams to ensure they understood the principles behind liquid ring vacuum pumps, and what extra checks they should be doing to ensure availability of the asset.

The solution was implemented and there have been no more failures.  Planned Preventive Maintenance was increased to monitor the assets, including regular vibration assessment using our Vibration Assessment and Management System (VAMS).

As a replacement for these units would cost in the region of £17,000, this solution prevented further failures and has reduced the client’s potential expenditure considerably.

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