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Understanding Volumetric Efficiency
of Reciprocating Pumps

By Joe Honeywell



Reciprocating pumps were one of the first pumps to be used in the industrial age and were primarily for water systems. The pump design has been refined over the years and now it is used in a wide variety of applications. Today, they are typically used in low-flow, high-head pumping conditions, but there are many exceptions. They still pump water but are also used with other types of liquids. While reciprocating pumps are not as popular as they once were, they still see a large demand in almost every industry.

Engineers are sometimes confused by the meaning of volumetric efficiency and how it relates to reciprocating pumps. The early applications of reciprocating pumps were not so concerned with volumetric efficiency, but that has changed just as the pump’s design has changed. Today’s process applications use higher pressures and compressible fluids, which has caused engineers to reevaluate the basic operation of reciprocating pumps. To add to the confusion, many pump suppliers furnish reciprocating pumps based on ideal (also called theoretical) conditions or from tests conducted with water. This can lead to confusion and operating problems, particularly if the process is sensitive to flow rate and the fluid’s physical properties. Understanding the meaning of volumetric efficiency becomes increasing important in today’s applications, especially those with large pump pressures and compressible liquids.

This paper will examine the definition of volumetric efficiency and how it affects the performance of a reciprocating pump. It will also examine how it is determined and factors that can cause it to vary. Example problems are presented along with a chart that shows how the pump performance can vary with different liquids. Finally, recommendations are presented for the use of volumetric efficiency in various applications.



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