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Centrifugal Pumps Operating in
Parallel Configuration

By Joe Honeywell

Introduction

The purpose of a pump is to add energy to a fluid. This increased energy is typically represented as a change in fluid pressure and velocity. However, other forms of energy such as temperature may apply. Because most pump applications can have a wide range of operating conditions, the amount of energy added can be significant. Since the energy is not free, economics should be considered in the effective management of the energy level increase. Another consideration when adding energy is how to control the amount of energy added. One of the most cost effective methods of increasing fluid energy over a wide range of flow conditions is to consider pumps operating in a parallel configuration.

A designer may want to consider various pump arrangements when evaluating the needs of a process. For example, a single pump may efficiently handle the flow requirements of a process. If the process conditions change then the fluid flow rate may need to increase or decrease. A common approach of handling the change is to configure one or more pumps in a parallel arrangement. Pumps would start and stop as the demand requires. In addition, multiple pumps may operate at higher efficiencies over a wider operating range. Of course, parallel pumps could be replaced with a much larger pump that handles the full operating range, but is this option the most effective? A single pump will most likely have a lower installed cost compared to multiple-pump installations. However, if the process operating conditions range widely, then the pump most likely will not operate near the best operating point, and the economics may favor multiple pump arrangements. Parallel pumps are another option that should be considered by the designer since this option has the flexibility to operate over a wide range of process conditions in an efficient manner.

Parallel pump arrangement can also influence the operating philosophy and design of a process. Multiple pumps are inherently more complex to control compared to a single pump. In addition, there are other issues related to the performance of parallel pumps that should be considered, such as matching the performance curve of each parallel pump, system reliability, degradation, and flow rate induced limitations. In essence, the operator and designer should understand all aspects of parallel pumps including the limitations and control complexities.

This paper will examine various topics related to pumps configured in parallel applications. Subjects discussed are typical applications of parallel pumps, hydraulics, design issues and operating issues. Finally, this paper will give an example problem which summarizes the performance of pumps operating in a parallel configuration.

 

 

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