Using Pump Curves

How to read Pump curves

With a pump specification, you’ll often see a graph with a curve, or series of curves. This is called a “pump curve” and it is the way the performance characteristics of a pump are described graphically. The pump curve describes the relation between flow-rate and the head for the pump.

Graph, Om2 water pump

What you’ll see on a pump curve:

  • Each curve is marked with the model number of the pump which performance it is describing. 
  • In the top right hand corner you will see the speed at which the pump(s) described operate at i.e “rpm” (revolutions per minute). The common motor speed for the UK is between 2800 and 3000 rpm. 
  • The flow rate of the pump is shown along the bottom of the graph as “Flow l/min”. The numbers indicate litres per minute. NB fuel pumps indicate this in reverse. 
  • How high the pump can pump liquid is shown up the left side of the graph as “Head m”. The numbers indicate the vertical distance in metres.

graph, water pumps

How to “read” the curve (using the above curve as an example):

  • Where the line ends on the right is the maximum rate at which it can pump. e.g. 195 l/min.
  • Where the line ends on the left is the maximum height this pump can pump to e.g. liquid stops coming out e.g. 7.5 metres
  • Calculate the head you are pumping at (inc. allowance for fittings, pipe material etc) e.g.at 4 metres
  • Go to this point on the left hand side of the graph
  • Move across the horizontal grid line to touch the curve line
  • Drop down the vertical line to touch the bottom line
  • The point where the vertical line touches the bottom line is the performance at the head.

Example: at a head of 4 metres, the OM2/OMA2 pump will pump 120 litres per minute.

PUMP GEEK: when you are selecting a pump you should aim for the pump to work in the middle third of a curve (e.g. on the above curve between 2 metres and 6 metres). Either side of this third and you run the risk of wasting energy and/or overloading the pump leading to damage. Failure of a pump used outside the middle third is not covered by our guarantee. Contact our sales department for assistance if you are not certain of your calculations. Ask for written confirmation that the pump you want to buy will be reliable for your application.