This pump type's unique system design requirements are often ignored or misapplied, which affects reliability and operation.
by Gary Dyson and Herb Tackett Jr.(Hydro, Inc.)
July 7, 2015
Figure 2. Fixed displaced volume – single-acting pump Figure 2. Fixed displaced volume – single-acting pump
Figures 3 and 4. Fixed displaced volume – double-acting pumpFigures 3 and 4. Fixed displaced volume – double-acting pump
Figures 5 and 6. Standard non-lubricated stuffing box designsFigures 5 and 6. Standard non-lubricated stuffing box designs

7. NPSHR

A centrifugal pump's net positive suction head required (NPSHR) is determined when the head has dropped 3 percent under reducing net positive suction head available (NPSHa) conditions.

For a reciprocating pump, 3 percent capacity drop is the criteria for defining NPSHR. NPSHa is reduced until the capacity drop has exceeded 3 percent.

The NPSH that was available at 3 percent capacity reduction is, by definition, established as the NPSHR.

A number of components can be modified to improve NPSHR. These modifications are much simpler than those required by a centrifugal machine.

Images 2 and 3. Ceramic plunger damageImages 2 and 3. Ceramic plunger damage

8. Belts

Many reciprocating machines still use drive belts over different diameter wheels to ensure that the speed of the machine is matched to the performance requirements. The type, number and fitting of the belts is important, and incorrect installation and application can cause failures.

Figures 9 and 10. Net positive suction head required determinationsFigures 9 and 10. Net positive suction head required determinations

9. Viscosity

When dealing with high viscosity, reciprocating machines perform considerably better than centrifugal machines. Reciprocating pumps can easily handle highly viscous liquids, and this viscosity has little effect on flow rate, which is not the case with centrifugal machines.

10. Training

Centrifugal pumps are widely understood, and their applications are common. Reciprocating pump specialist training can greatly improve the understanding of these machines and help users improve their performance and reliability.

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