Two Basic Requirements for Trouble-Free Operation of Centrifugal Pumps

Centrifugal pumps are the ultimate in simplicity. In general there are two basicrequirements that have to be met at all the times for a trouble free operation and longerservice life of centrifugal pumps.The first requirement is that no cavitation of the pump occurs throughout thebroad operating range and the second requirement is that a certain minimum continuousflow is always maintained during operation.A clear understanding of the concept of cavitation, its symptoms, its causes, andits consequences is very much essential in effective analyses and troubleshooting of thecavitation problem.Just like there are many forms of cavitation, each demanding a unique solution,there are a number of unfavorable conditions which may occur separately orsimultaneously when the pump is operated at reduced flows. Some include:o Cases of heavy leakages from the casing, seal, and stuffing boxo Deflection and shearing of shaftso Seizure of pump internalso Close tolerances erosiono Separation cavitationo Product quality degradationo Excessive hydraulic thrusto Premature bearing failuresEach condition may dictate a different minimum flow low requirement. The finaldecision on recommended minimum flow is taken after careful “techno-economical”analysis by both the pump user and the manufacturer.The consequences of prolonged conditions of cavitation and low flow operationcan be disastrous for both the Centrifugal Pumps and the process. Such failures in hydrocarbonservices have often caused damaging fires resulting in loss of machine, production, andworst of all, human life.Thus, such situations must be avoided at all cost whether involving modificationsin the Centrifugal Pumps and its piping or altering the operating conditions. Proper selection andsizing of pump and its associated piping can not only eliminate the chances of cavitationand low flow operation but also significantly decrease their harmful effects.