How to Read a Pump Performance Curve Without an Engineering Degree
Every pump performance curve says the same thing: the higher you push, the less you move.
A pump performance curve is a graph showing how much flow a pump delivers at each height it has to push. Head runs up the side, flow runs along the bottom, and the line slopes down. Find your head on the side, go across to the line, drop straight down, and that is your real flow. It takes ten seconds, and it decides whether you are buying the right pump.
The two big numbers in any brochure, maximum head and maximum flow, are the two ends of that line. You never get both, and you rarely want to be near either. The pump you should buy is the one with your duty point in the middle of its curve.
Short on time? Put your job into the pump station sizing calculator, or see the Kwikflo 900L sewer station and REEFE RGM055A 250L package, our two most common answers.
The four things on a pump curve
A pump curve has four things worth reading: the head axis, the flow axis, the shutoff point and the runout point.
| Part of the curve | What it means | Why you care |
|---|---|---|
| Head (vertical axis) | Metres the pump pushes, lift plus friction | This is the number you calculate |
| Flow (horizontal axis) | Litres per minute or per second | This is the number you read off |
| Shutoff (top left) | Maximum head, where flow is zero | The brochure number. Useless as a working figure |
| Runout (bottom right) | Maximum flow, where head is close to zero | The other brochure number. Nothing real runs there |
Note the units before you read anything. Some curves use L/s, some L/min, some m³/h. Multiply L/s by 60 to get L/min. A 5 L/s pump and a 300 L/min pump are the same thing, and that mix up has sold plenty of wrong pumps.
How to find your duty point in three steps
Your duty point is where your calculated head meets the pump curve, and finding it takes three steps.
- Work out total head. Static lift from the low water level to the highest point of the pipe, plus friction in the pipe and fittings. Our head height guide walks through it.
- Go across. Find that head on the vertical axis and run across to the curve.
- Drop down. Read the flow directly below. That is what the pump will do on your site.
Then ask one question. Is that flow enough? On a sewer rising main, the usual rule of thumb is to keep velocity at about 0.75 m/s so solids stay moving. In a pipe with a 50 mm internal diameter that takes about 90 L/min. In a 40 mm bore it takes about 57 L/min. If your duty point sits below that figure, the pipe will slowly fill with settled solids, however happily the pump seems to run.
Why maximum head is the wrong number to compare
Maximum head is the wrong number to compare because a pump delivers nothing at all at that height. A pump rated to 10 metres delivers zero flow at 10 metres. Published rated points tell you far more, and here are four real pumps we sell.
| Pump | Maximum head | Maximum flow | Rated point | Price |
|---|---|---|---|---|
| REEFE RVC260 | 10.5 m | 280 L/min | 140 L/min at 5.6 m | $790 |
| REEFE RVS300 | 10 m | 300 L/min | 220 L/min at 5 m | $899 |
| REEFE RCE90 | 11.4 m | 403 L/min | 300 L/min at 3.2 m | $1,302 |
| REEFE RCE160 | 18.25 m | 461 L/min | 300 L/min at 7.5 m | $1,727 |
Prices current as of November 2026, AUD including GST. Figures from each product listing, with L/s converted to L/min.
Look at the first two rows. On maximum head, the RVC260 wins. At working head, the RVS300 is clearly ahead, moving 220 L/min at 5 metres while the RVC260 gives 140 L/min at 5.6 metres. Buying off the headline number gets that backwards.
The last two rows make the same point another way. Both cutter pumps are rated at 300 L/min, but the RCE160 holds it at 7.5 metres and the RCE90 only at 3.2 metres. If your job is 6 metres of head, the extra $425 is not optional.
Where your duty point should sit on the curve
Your duty point should sit around the middle of the pump curve, away from both ends. That is where a pump usually runs best, and it leaves margin for what you did not count.
- Too close to shutoff: tiny flow, long run times, solids settling in the pipe, and a pump with no reserve for a partly blocked line.
- Too close to runout: the pump is oversized for the head, draws more current, and can trip on overload or wear early.
- In the middle: a steady flow, sensible run times, and room for pipe ageing and pump wear.
A real example: the REEFE RGM055A 250L station at $3,305 has a pump with 10 metres of maximum head and 160 L/min of maximum flow. We treat it as comfortable under about 5 metres of total head. Past that, step up to a station like the Kwikflo 900L sewer station at $4,699, or a grinder package.
Why your real flow can be lower than the curve
Your real flow can be lower than the curve because a published curve assumes a new pump, clean water and the rated supply voltage. Site conditions are never that tidy.
- Friction was underestimated. This is the usual one. On long runs of small pipe, friction can exceed the lift. Our rising main friction loss guide has worked numbers.
- Wear. Impellers and cutters lose performance over the years.
- A partly closed or sticking valve. A non-return valve full of rag adds head that was never in your sums.
- Low voltage. A long cable run can shave performance. Your electrician can check it.
Allow margin. If your sums land at exactly the pump's limit, that is a warning, not a match.
What two pumps do to the curve
Two identical pumps running together do not deliver double the flow into the same pipe. Each pump's flow adds, but pipe friction rises as flow rises, so the system pushes back and the combined duty point lands short of double. In most duty and standby stations, the second pump is there for reliability, not extra capacity. Our dual pump station guide covers when that matters.
Frequently asked questions
What is a pump performance curve?
A pump performance curve is a graph that shows the flow a pump delivers at each head. Head sits on the vertical axis and flow on the horizontal axis. The line slopes down, because a pump moves less water the higher it has to push.
What is the duty point on a pump curve?
The duty point is where your calculated total head meets the pump curve. It shows the flow that pump will actually deliver on your site. A well chosen pump has its duty point near the middle of the curve.
What does maximum head mean on a pump?
Maximum head is the height at which a pump delivers zero flow, also called shutoff head. It is a limit, not a working figure. A pump with 10 metres of maximum head delivers nothing at 10 metres, so always size from the curve.
What happens if a pump runs off its curve?
A pump running near either end of its curve wears faster and performs poorly. Near shutoff it moves little water and solids can settle in the pipe. Near runout it can draw excess current and trip its overload protection.
Where do I find the pump curve for a pump in Australia?
The pump curve is usually in the manufacturer's brochure or specification sheet, which most Waternex product pages link under downloads. If you cannot find one for your model, send us the pump name and your head and we will check the duty point.
Want someone to check the curve for you?
Send us the lift, the pipe length and size, and your power supply, and we will tell you where your duty point lands and which pump suits it. Contact us here, or call 1300 930 847.
This guide is general information for Australian conditions and is not a substitute for advice from a licensed plumber. Pump station installation and sewer connection are regulated work, and requirements differ between states and water authorities. Rules of thumb are starting points, and final sizing should be confirmed against the manufacturer's curve for the specific pump.