# Pump pressure and flow

## Main Question or Discussion Point

hi guys,

what is meant by rated pressure and flow of a pump... Is that maximum pressure or flow..but then i have seen 150% of rated flow?? How is that possible ?? please clarify my doubts...

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CWatters
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Pumps are specified many different ways. Typically they are designed to deliver a specified flow rate at a specified pressure determined by the application. That operating point might be defined as 100%. Under those conditions they will consume a specified amount of power and the motor will be designed accordingly.

If you connect such a pump to an open pipe the output pressure might be virtually zero. Under those conditions the motor may speed up and increase the flow rate beyond 100%. The power consumption might be lower than maximum rated.

If you connect such a pump to a severe restriction that may result in the flow being restricted. The output pressure increasing beyond 100% of it's nominal rating and the flow rate reducing. The power consumption might be higher than the nominal rating. Generally it's not a good idea to stall a pump like this.

Exactly how the pump behaves will depend on the type of motor used and any controls. It's possible to make a pump that, over a limited range, is controlled so that it produces either a constant flow rate or a constant pressure.

Take a look at some data sheets. Look for graphs of pressure vs flow rate.

PS In some cases manufacturers specify a maximum pressure and maximum flow rate. If these figures are really the "pressure at zero flow rate" and the "flow rate at zero pressure" then threat with care. Your actual operating point will normally lie somewhere in between. It's not always safe to assume you can draw a straight line between these two points.

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