Positive displacement pump failures

SYMPTOMS AND CAUSES OF FAILURE FOR POSITIVE DISPLACEMENT PUMPS... 

Most hydraulic systems use a positive displacement pump to generate energy within the system. Unless the pressure is controlled, these pumps will generate excessive pressure that can cause catastrophic failure of system component. A relief valve is always installed downstream of the hydraulic pump to prevent excessive pressure and to provide a positive relief should a problem develop within the system. The relief valve is designed to open at a preset system pressure. When the valve opens, it diverts flow to the receiver tank or reservoir. 

Design, installation, and operation are the dominant factors that affect a pump s mode of failure. This section identifies common failures for centrifugal and positive-displacement pumps. 

Table 21.2 Common failure modes of rotary-type, positive-displacement pumps...

Positive-displacement pumps are more tolerant to variations in system demands and pressures than centrifugal pumps. However, they are still subject to a variety of common failure modes caused direcdy or indirectly by the process. 

Rotary-type, positive-displacement pumps share many common failure modes with centrifugal pumps. Both types of pumps ate subject to process-induced failures caused by demands that exceed the pump s capabilities. Process-induced failures are also caused by operating methods that either result in radical changes in their operating envelope or instability in the process system. 

Table 21.2 lists common failure modes for rotary-type, positive-displacement pumps. The most common failure modes of these pumps ate generally attributed to problems with the suction supply. They must have a constant volume of clean liquid in order to function properly. 

Table 21.3 lists the common failure modes for reciprocating-type, positive-displacement pumps. Reciprocating pumps can generally withstand more abuse and variations in system demand than any other type. However, they must have a consistent supply of relatively clean liquid in order to function properly. 

Blowers, or positive-displacement fans, have the same common failure modes as rotary pumps and compressors. Table 13.4 lists the failure modes that most often affect blowers and fluidizers. In particular, blower failures occur due to process instability, caused by start/stop operation and demand variations, and mechanical failures due to close tolerances. 

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