Our founder Simon Crowther filmed a short YouTube video, "How to Read a Pump Curve", back in 2023. Two years on it has amassed a significant 33,000 views, so we thought it was time to turn it into a blog too, because a pump curve is one of those things people see on a spec sheet and think, "what on earth does that mean?" This is the written version for anyone who prefers to read rather than watch, and the video is at the bottom of the page.
What is a pump curve?
When you look at a pump specification sheet, you will often see a small graph with a curved line across it. That is the pump curve, sometimes called a pump graph or performance curve. It is the simplest way to show what a pump can do: how much water it can move, how quickly, and how high. It looks technical at first glance, but once you know what you are looking for it is straightforward, so approach it with an open mind and do not be intimidated. Understanding it properly can save you time, money and frustration. Get it wrong and you might end up with a pump that burns out or simply does not do the job.
Breaking it down
Think of the pump curve as a performance chart, and check what each axis represents. Along the horizontal axis you will most often have the flow rate, usually in litres per minute, which tells you how much water the pump can move in a set time. Up the vertical side you will usually have the head, which is how high the pump can push water vertically, measured in metres. Imagine pumping straight up through a pipe: the head is the maximum height the pump can lift water before nothing comes out of the other end. Head is also a measure of pressure. For water, 10m of head is about equal to 1 bar.
Calculating head loss
As a very rough rule, every ten metres of horizontal distance equals about one metre of head loss. So if you are pumping across a garden or driveway, those extra metres make a real difference, and it is useful to understand this when working out the flow rate you will actually achieve. A 90 degree bend, as a rule of thumb, adds about another metre of head loss. This is of course very approximate, and for detailed scenarios we would always recommend calculating the flow rate more accurately and considering friction loss through the pipe. A very small pipe means much more friction loss and a lower flow rate, which is why on certain pumps, such as the Tsurumi LSC1.4S or APP HD-15, there are options to increase the outlet size depending on your requirement. Our Water Pump Performance Calculator will estimate the friction part for your pipe run.
We are not able to advise on site-specific requirements over the phone, as that needs analysis of the whole pipe network, connections and distances, which is a service for a consulting engineer. In most instances, though, a quick calculation helps determine which pump to use. For a project from the ground up, we would always recommend engaging an engineer first.
An example from the video
In the video, Simon uses the Tsurumi LSC1.4S puddle pump as an example. On its curve, at zero height (no lift at all) it moves around 170 litres per minute. At its maximum head of 11 metres the flow rate drops to zero, which is the limit. The ideal operating range is somewhere in the middle of the curve, where the pump runs efficiently without strain. Running it at 11m of head is like asking a small car to tow a caravan up a hill: it will struggle, manage very little speed (flow rate), and probably cause engine damage. At the other end, with no head at all, it is like driving the car flat out in first gear, which over time also causes damage. For occasional use it matters less, but for a fixed installation in frequent use you want to run around the mid-point of the curve. Too far either side risks premature failure and could invalidate the warranty. For more on this, including the duty point and the middle-third rule, see our deeper guide, How to Read a Pump Curve and Choose the Right Pump.
Working out your own setup
Imagine you are pumping from a cellar two metres deep. The water needs to go ten metres across your garden, which (using the rule of thumb) adds another metre of head loss, and you have one right-angled bend, which adds another metre. In total that is roughly four metres of head. Find four metres on the vertical axis, follow it across to the curve, then read down to the flow rate, in this case around 150 litres per minute. That is roughly what you can expect once everything is connected and running.
Why it is worth knowing
Reading a pump curve means you can choose the right pump, run it efficiently and avoid unnecessary wear. Once you get the hang of it, it becomes second nature, something you will use every time you set up a pump or drainage system.
Watch the video
If you need a hand choosing a pump, our team are happy to help on 0115 987 0358, or use the Pump Finder. For more detailed support designing a drainage scheme or specifying a system, which often cannot simply be bought online, we recommend our sister company FPS Environmental Ltd, a team of consulting engineers who can model drainage systems, calculate friction loss and ensure every element is properly designed. You can also ask about our Engineering Review Service.
