Our Founder, Simon Crowther filmed and shared a short video on Youtube, “How to Read a Pump Curve” in 2023, and two years later, at the time of writing this blog, in 2025, it has amassed a significant 33,000 views. Therefore, we thought it was time we converted the video into a handy blog too, because it’s one of those things people see on a spec sheet and think, “What on earth does that mean?”
This blog is the written version for anyone who prefers to read rather than watch. The video is at the bottom of the page if you’d like to see it in action.
When you look at a pump specification sheet, you’ll often see a small graph with a curved line across it. That’s called a pump curve, or pump graph. It can even be referred to as a performance curve.
It’s the simplest way to show what a pump can do, how much water it can move, how quickly, and how high it can move it. It effectively shows the characteristics of a water pump. It looks quite technical at first glance, but once you know what you’re looking for, it’s straightforward, and it is best to approach it with an open mind and to not be intimidated. By the end of this blog, or video, you’ll know what they are, and how to read them.
Understanding it properly can save you a lot of time, money, and frustration. Get it wrong, and you might end up with a pump that either burns out or simply doesn’t do the job you expected.
Think of the pump curve as a performance chart. It’s important to check what each axis represents (the x and y axis, or the vertical and horizontal axis if we’re keeping it simple).
Along the horizontal axis, you will most often have the flow rate, usually shown in litres per minute. That tells you how much water the pump can move in a set time period.
Up the vertical side, you will usually have the head, which is how high the pump can push the water vertically, measured in metres. Imagine pumping straight up through a pipe. The head is the maximum height the pump can lift water before it stops coming out of the other end. Head is a measure of “pressure”. For water, 10m of head is about equal to 1 bar of pressure.
As a very rough rule, every ten metres of horizontal distance equals about one metre of head loss. So if you’re pumping across a garden or driveway, those extra metres can make a real difference, and it is useful to understand this when calculating the flow rate you’re likely to achieve at the end of the pump. A 90 degree bend for instance as a rule of thumb would be another metre of head loss. This is of course very “rule of thumb” and for detailed scenarios we would always recommend calculating the flow rate more accurately and considering aspects such as friction loss through the pipe. If you use a very small pipe, you’ll have much more friction loss, and therefore 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 size of the outlet depending on your requirement.
Unfortunately, we’re not able to advise on site specific requirements over the phone as we’d need to analyse every detail regarding the pipe network, connections, distance etc, and this would be a service undertaken by a consulting engineer. However, in most instances a quick calculation can assist with determining which pump to use. If you have a very specific situation, or are looking at a project from the ground up – we would always recommend engaging with an engineer first to specify what is needed.
In the video, Simon uses the Tsurumi LSC1.4S Puddle Pump as an example.
On its pump curve, you can see that at zero height (so no lift at all) it moves around 170 litres per minute. At its maximum head of 11 metres, the flow rate drops to zero, that’s the limit.
The ideal operating range is somewhere in the middle of the curve. That’s where the pump runs efficiently without strain.
Running it at the extreme end with 11m of head is like asking a small engine car to tow a caravan up a hill, it will struggle, have very limited speed (flow rate), and probably cause engine damage. At the other end of the scale, you’ve no head at all, that is more like driving the car flat out in first gear, and again over time that can cause damage too. For occasional or short term use, it is less likely to matter, but for a fixed installation and frequent use, you really want to be running around the mid-point of the curve. Too far either side and it will risk premature failure and could invalidate the warranty.
For example, imagine you’re pumping from a cellar that’s 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’ve got one right-angled bend in the pipework, that’s another metre.
In total, that’s roughly four metres of head.
If you look at the pump curve, you can find four metres on the vertical axis and follow it across until it meets the curve. Then read down to find the flow rate, in this case, around 150 litres per minute. That’s roughly what you can expect once everything is connected and running.
Understanding how to read a pump curve means you can choose the right pump, run it efficiently, and avoid unnecessary wear and tear. Once you get the hang of it, it becomes second nature, something you’ll use every time you’re setting up a pump or drainage system.
If you’d prefer to see a visual walkthrough, the video below explains exactly how to read a pump curve step by step.
Need a Hand?
If you need a hand choosing a water pump, our team at FloodandWaterPumps.co.uk are happy to help.
We’ll keep sharing more short videos and blogs like this one to make flood resilience and pump selection easier to understand.
For anyone who needs more detailed support with designing a drainage scheme or specifying a system, this often isn’t something that can simply be bought or found online. We recommend speaking with our sister company, FPS Environmental Ltd, a team of experienced consulting engineers who can model drainage systems, calculate friction loss, determine requirements, and ensure every element is properly designed and specified.
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