# Pump parallel and series operation

Section summary
1. Definition
2. Calculation
3. Precautions

## 1. What is parallel and series pumping

It is sometimes necessary to use pumps in parallel or in series.

Parallel operation allows to add the pump capacities.

Some precautions are however necessary when operating pumps in parallel or series (see corresponding section)

## 2. How to operate pumps in parallel or series

All calculations are performed thanks to the pump characteristics established by the supplier. This document is necessary for design parallel and series pumping systems. A typical pump characteristic curve is represented below, for a centrifugal pump.

Figure 1 : Pump NPSH, required and available

Reading and undertanding the pump characteristic curve is a very important 1st test for pipe circuit calculation.

In pump parallel operation, both pump will deliver the flow they have been designed for, at the given head of the combined flow. The characteristic of the parallel pumping system can be calculated by adding the capacity of each pump at a given head.

Figure 2 : Building resulting characteristic of 2 pumps in parallel

However, it must be noted the following : the combined flow is requiring a higher head for a given system curve, thus the combined capacity Q3 of the system is not equal to Q1 + Q2 when the pumps are running one by one. This is illustrated on the graph below by the system curve.

Figure 3 : Flow in a system with pump in parallel