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Technology Fluid Handling/Maintenance
Key Concepts
* Pump reliability can be predicted.
* Mechanical seals and bearings cause most pump failures.
* Pump packages with monitors and controls can help prevent pump failure.
Over the past ten years, pump users have made progress toward improving pump reliability. Much of it came from total quality (TQ) initiatives where tools such as root-cause failure analysis, statistical analysis techniques, and a heightened awareness were used. Education through "best practice" forums has allowed users to identify the issues that account for a significant portion of pump failures and downtime.
Since that time most users have or are implementing reliability improvement programs. These involve activities that allow them to identify and execute corrective actions long before equipment failure occurs. The result is increased meantime-between-failure (MTBF) intervals.
The results of these initiatives have been impressive. Surveys of pump users in the North American chemical industry have shown typical improvements in MTBF between 15 and 24 months.
While these improvements have helped many companies improve profitability and maintain competitiveness, the ever-increasing pressures of today's marketplace have many users looking for additional measures to further increase MTBF and maintain their competitive edge.
Analyzing the actions taken to date shows the focus has been primarily on improving the mechanical aspects of equipment reliability. A holistic approach is needed to gain a better understanding of how a pump functions within a system.
Robust pump selections
During the design process of a pumping system designers and engineers consider many variables. One area to consider, which can improve pump reliability, is the criteria used to select and hydraulically size pumps.
Over the years there have been many guidelines and unwritten rules established to help engineers specify pumps. Basic selection criteria often included objectives such as selecting a pump to operate at its best efficiency point (BEP), running at slower speeds, and providing adequate net positive suction head (NPSH). While these all represent sound engineering practices, often, in real world applications, it is not practical or possible to meet all of these criteria. The engineer is left to make a subjective judgment as to which pump is best for a given service.
Three common factors, which are pertinent to most pump selections, are operating speed, impeller...