When water travels through a hose or pipe, it loses pressure due to friction against the pipe walls. This is known as friction loss, and it directly affects how much useful output your pump delivers on site. This calculator combines friction loss and an indicative duty point estimate. Enter your pump's published figures alongside your hose details to see the flow rate you are likely to achieve in practice. All results are indicative only and should always be verified against your pump's published performance curve before making a final selection.
Indicative only
This calculator uses a simplified parabolic pump curve and the Hazen-Williams friction loss formula. Real pump curves vary by model. Results are a guide only — always verify against your pump's published performance data and consult our team if you are unsure.
How to use this calculator
- Enter your pump's max flow rate and max head from the datasheet or product listing. These are the peak figures at either end of the pump curve — max flow at zero head, max head at zero flow.
- Select your hose or pipe type. Suction and delivery hose is the most common for portable pumps. Layflat hose is used for longer water transfer runs. Rigid PVC pipe is for fixed installations.
- Choose the diameter to match your pump outlet or the hose you intend to use.
- Enter the total length of your hose or pipe run in metres from pump outlet to discharge point.
- For rigid pipe, add any 90 degree bends using the counter. Each bend adds resistance equivalent to extra pipe length.
- Read the results. The calculator estimates your duty point — the flow rate and head your pump will likely deliver through that hose run. For longest pump life, aim for a duty point in the mid-curve range (roughly 40 to 70% of max flow).
Step 1 — Your pump specification
Labelled "max flow" or "free flow" on the datasheet — the flow at zero back pressure
Labelled "max head" or "total head" — the maximum height the pump can push water at zero flow
Step 2 — Your hose or pipe
Suction / delivery hose
PVC reinforced, helix coil, smooth bore — max 6 bar working pressure
Vertical rise from pump to outlet. Enter 0 if pumping on flat ground
Results
Friction loss per 10 m
—
m head / 10m
Total friction loss
—
metres head
Head remaining after friction
—
metres head
Estimated flow at duty point
—
L/min (indicative)
What is friction loss and why does it matter?
Friction loss is the reduction in pressure that occurs as water flows through a hose or pipe. It is caused by resistance between the water and the pipe walls, and it means the pressure available at the end of your hose run is always lower than what your pump produces at its outlet.
This matters because your pump's published figures, max flow and max head, are measured under ideal laboratory conditions with no hose attached. The moment you connect a hose on site, friction loss begins to reduce both the effective head and the achievable flow rate. On longer runs or with narrower hoses, this reduction can be significant.
Understanding friction loss before you buy or deploy a pump helps you choose the right hose diameter, avoid running a pump outside its efficient operating range, and get the performance you actually need on site.
What affects friction loss?
Several factors determine how much friction loss occurs in a hose or pipe run.
- Diameter is the single most important factor. Friction loss increases dramatically as the bore gets smaller. At the same flow rate, a 32 mm hose can produce more than ten times the friction loss of a 50 mm hose. Upsizing your hose diameter is almost always the most cost-effective way to reduce friction loss.
- Length has a direct, linear relationship with friction loss. Every additional metre of hose adds proportionally to the total. On runs of 50 metres or more, friction loss can consume a significant portion of your pump's available head.
- Flow rate has a disproportionate effect. The Hazen-Williams formula used in this calculator shows that friction loss increases roughly with the square of the flow velocity. Doubling the flow rate more than doubles friction loss.
- Hose type affects the friction coefficient. Smooth-bore suction and delivery hose has a relatively low coefficient. Layflat hose has a higher coefficient because the bore is not perfectly circular under flow. Rigid PVC pipe has the lowest friction loss of the three, provided bends and fittings are kept to a minimum.
- Bends and fittings add resistance that is easy to overlook. Each 90 degree bend is equivalent to approximately 30 times the pipe diameter in additional straight pipe length. On a 50 mm rigid pipe installation with four bends, that adds 6 metres of equivalent pipe length before a single metre of straight run is counted.
What is mid-curve operation and why does it matter?
A pump curve shows the relationship between flow rate and head. At one end, the pump produces maximum head at zero flow. At the other, it produces maximum flow at zero head. Neither extreme is where a pump should run for extended periods.
The mid-curve range, roughly 40 to 70% of the pump's maximum flow rate, is where a pump operates most efficiently. In this range the pump is neither working against excessive resistance nor running too freely. Energy consumption is lower, heat generation is reduced, and the pump experiences less mechanical stress, which directly extends its working life.
Running a pump near its maximum flow rate, or near its maximum head, reduces efficiency and can cause overheating, cavitation, and premature wear. This is why the calculator flags duty points outside the mid-curve range with a warning. Not because the pump will not work, but because it will not work as well or last as long.
When selecting a pump for a given application, always aim for a duty point that sits comfortably in the mid-curve range. If your estimated duty point is outside that range, consider adjusting your hose diameter or run length before changing the pump.
Choosing the right hose size
As a general rule, always match your hose diameter to your pump outlet size, or go larger if the option exists. Running a hose that is smaller than the pump outlet creates a bottleneck that increases friction loss and reduces performance regardless of how powerful the pump is.
For most portable pump applications in the UK, including flood water removal, site dewatering, and water transfer, a 50 mm (2") hose is the most practical choice. It balances manageable weight with good flow capacity. For higher flow rates or longer runs, an 80 mm (3") hose will significantly reduce friction losses and help keep the duty point in the mid-curve range.
If your application requires a high flow rate over a long distance, consider splitting the run using two parallel hoses rather than extending a single hose. This halves the velocity in each hose and dramatically reduces total friction loss across the system.
Frequently Asked Questions
What is friction loss?
What is friction loss?
Friction loss is the reduction in pressure that occurs as water flows through a hose or pipe. The longer or narrower your hose, and the higher your flow rate, the more pressure is lost, leaving less available at the outlet. Ignoring friction loss is one of the most common reasons a pump underperforms on site.
Are these results accurate?
The results from this calculator are indicative only. They are based on the Hazen-Williams formula using standard friction coefficients for each hose type. Real-world results will vary depending on hose condition, age, fittings, bends not accounted for, and the actual pump curve of your specific pump. Use these figures as a guide for selection and always verify against manufacturer data before finalising your choice.
Which hose type has the most friction loss?
Layflat hose has the highest friction loss because it is not perfectly circular under flow, the bore deforms slightly, increasing resistance. Suction and delivery hose has a smooth, rigid bore so performs better. Rigid PVC pipe has the lowest friction loss of the three.
Does hose diameter make a big difference?
Yes, significantly. Friction loss increases dramatically as diameter reduces. Going from a 50 mm hose to a 32 mm hose at the same flow rate can multiply friction loss several times over. If your pump is underperforming, upsizing the hose diameter is often the most cost-effective fix.
What does "metres head" mean?
Head is a way of expressing pressure as a height of water. One metre head is equivalent to roughly 0.098 bar. Your pump's datasheet will quote its maximum head, subtract your friction loss to find how much useful head is left for your application.
How do 90° bends affect friction loss?
Each 90° bend or elbow adds resistance equivalent to approximately 30 times the pipe diameter in extra straight pipe length. For example, a bend in a 50 mm pipe adds roughly 1.5 m of equivalent pipe length. Use the bend counter in the rigid pipe tab to account for these.
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