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Centrifugal Pumps, how pressure affects performance

Cole-Parmer Sealless PVDF Centrifugal Pump 72223_20

How pressure affects centrifugal pumps

For many operations, premium pump performance translates into more efficient production. In other words, when pumps aren’t operating to the best of their abilities, it can slow everything down.

The keys 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.

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, 100L/min. No pressure is generated in this setup, so the pump has an unobstructed path.

Cole-Parmer Sealless PVDF Centrifugal Pump 72223_20

Cole-Parmer Sealless PVDF Centrifugal Pump

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 6m tall tank. Pumping up will create pressure and slow the pump rate down
  • Pumping into a filter, which generates pressure, which slows the pump down
  • Pumping across a long horizontal distance (perhaps 15-18m) with loss of pressure due to friction
  • Setup with loops, which create intermittent pressure

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

Here’s how to compensate for setup conditions resulting in a less-than-ideal maximum flow rate:

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 high 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, find ways to adjust to safely reach the maximum flow rate. Solutions include:Centrifigal Pumps Pump-Curve Cole-Parmer

  • For setups that pump fluid up vertically, our 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 our 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 pressure generated. Experts recommend a slightly oversized pump for this reason. A more powerful centrifugal pump can handle higher maximum head pressure. Prevent future headaches by getting a little more power than you need.

 

View our selection of Centrifugal Pumps as well as general Pumps
Our Technical Experts would love to hear from you
AUS Freecall Ph. 1800 552 724 and NZ Freecall Ph. 0800 651 700
Email: info@johnmorris.com.au

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