Pump Performance Predicting Your Pumps Performance

Editor: Dominik Stephan

Premium pump performance translates into more efficient production – Flow rate and pressure are key to pump efficiency. Read on to know more about the performance of pumps in a given environment.

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Different conditions affect the output of the pump and it may not deliver the maximum flow rate stated.
Different conditions affect the output of the pump and it may not deliver the maximum flow rate stated.
(Source: Cole-Parmer India)

When pumps are not operating to the best of their abilities, it can slow everything down. The key to pump efficiency, in most cases, are flow rate and pressure. Determining maximum flow rate with pressure constraints in a setup can be tricky.

For example, with peristaltic pumps, the maximum flow rate is dependent on several variables, including tubing formulation and size, along with the viscosity of the fluid to be pumped. The equation between flow rate and pressure is not an easy one to determine without considering the contributing variables.

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However, with centrifugal pumps, the relationship between maximum flow rate and pressure is much more predictable. When the setup is a straight, open path without obstacles or turns, the maximum flow rate should be what is stated for the size of centrifugal pump purchased.

This may be, for example, 100 L/min. No pressure is generated in this setup, so the pump has an unobstructed path. Yet, in many facilities this is not possible. The pump setup may be any of the following:

  • Pump is positioned on the floor and pumping into a 20 ft tall tank. Pumping up will create pressure and slow the pump rate down
  • Pumping into a filter, which generates pressure, and slows the pump down
  • Pumping across a long horizontal distance (perhaps 50–60 feet) with loss of pressure due to friction
  • Setup with loops, which creates intermittent pressure

As each of these conditions affect the output of the pump, it may not deliver the maximum flow rate stated.

Typically, centrifugal pumps are used for high volume, mostly industrial applications such as batch transfer or evacuating tanks. Users want efficiency in the form of a high flow rate without a hefty price tag. The high flow rate can be compromised by a setup that generates high pressure. When the maximum pressure is reached, the pump deadheads.

When pressure is introduced into the setup, one has to find ways to safely reach the maximum flow rate. The solutions are as follows:

(Please refer to the graph)

  • For setups that pump fluid up vertically, the company’s technical support experts can calculate the pressure
  • For those adept at reading flow curves, these curves are available to show what the maximum flow rate should be, given the application-specific pressure
  • Use a pressure gauge at the end of the line to determine the pressure; if unsure of results, contact the company’s technical support experts. With the pressure gauge reading, they will ask the desired flow rate and make a recommendation
  • When using filters, the pressure may change as the filter fouls; another type of pump such as a peristaltic pump may be advised

When choosing a centrifugal pump, select the correct pump size to compensate for the pressure generated. Experts recommend a slightly oversized pump for this reason. A more powerful centrifugal pump can handle higher maximum head pressure. One can prevent future headaches by getting a little more power than required.

* First published in PROCESS Worldwide Subcontinent Edition 01/2016

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