Which Pump Do I Need?
UK Flow Centre buying guide
Choose a pump from the duty, not the horsepower
A pump needs to move the required amount of water at the required pressure and height. A bigger motor alone does not guarantee the right result.
1. Start with the job
2. Match the pump type to the water
- Clean-water transfer or irrigation: check the flow required at the working pressure.
- Tank boosting: consider water level, automatic control, dry-run protection and the outlet demand.
- Drainage or dirty water: check the permitted solids, the lift and the discharge route; do not assume a clean-water pump is suitable.
- Submersible or surface pump: choose around where the pump will physically sit and how it will be supplied with water.
3. Gather the five facts
- Water source and water condition.
- Required flow or number of outlets running together.
- Vertical lift from water level to discharge point.
- Pipe diameter, total length and major restrictions.
- Available electrical supply and preferred control method.
4. Product routes that illustrate the main pump types
These examples show why the installation comes before the model. They are not interchangeable, and none should be selected from maximum flow or maximum head alone.
5. Turn the job into a duty point
Required pump head is approximately: vertical lift + pressure needed at the outlet + losses through the pipe, fittings, valves and filters.
For clean water near normal temperatures, 1 bar is about 10.2 metres of water head. If an outlet needs 2.5 bar and sits 5 metres above the lowest operating water level, the starting requirement is about 30.5 metres head before pipe and fitting losses are added.
The pump curve must still show the required flow at that total head. The real operating point is where the pump curve meets the system curve, so the maximum flow and maximum head printed on a box cannot be used together.
Technical reference: Grundfos explanation of pump curves.
6. Measure what the system is doing
Use running readings, not static pressure alone
Measure pressure while the intended outlets are operating and record the flow at the same time. A closed-system static reading cannot show whether the source, pump and pipework can maintain pressure at the required demand.
A Pressure Gauge – 160 psi / 11 Bar can help, but first confirm that its range, connection and installation method are suitable for the test point.
7. Plan the system around it
Also allow for suitable suction or delivery pipework, isolation, non-return protection where needed, filtration where appropriate, pressure control and electrical protection. The pump is one part of the system.
Keep the pump, curve and installed revision together
Save the manufacturer, complete model and suffix, article code, supply frequency, control mode and the document number or revision of the curve used. Record P1 and P2 exactly as the manufacturer defines them; P1 is commonly electrical input and P2 motor shaft output, not delivered hydraulic power. If the nameplate and curve cannot be tied to the same product revision, keep the selection open.
Where a borehole, rainwater system or other source fills a tank, treat source-to-storage and storage-to-irrigation as two duties. The transfer pump is limited by source availability and refill rate; the irrigation pump must meet the peak zone flow and total head. Read the borehole guide and plan the storage route.
Quick choice
- Watering a few zones: establish the flow and pressure each zone needs first.
- Boosting a tank supply: start with the demand and the control method, not the largest pump available.
- Removing water: choose around the water condition, lift and discharge pipe size.
Quick pump-selection questions
Can I choose a pump from its maximum flow figure?
No. Maximum flow and maximum head sit at opposite ends of the pump curve. Choose from the flow the pump can deliver at your system's actual working pressure and lift.
What information do I need before choosing a pump?
Record the water source and condition, required flow or number of outlets, vertical lift, pipe diameter and length, major restrictions, electrical supply and preferred control method.
Do I need to plan more than the pump?
Yes. Allow for suitable suction or delivery pipework, isolation, non-return protection where needed, filtration where appropriate, pressure control and electrical protection.
Shop pumps Pump not priming? Read the fault-finding guide
Technical guidance from UK Flow Centre, operated by JK Irrigation Ltd. Explore all guides in the Technical Hub.
Using a water butt for garden watering
A gravity outlet can fill a watering can, but it does not provide mains-like pressure. For hose, dripline or sprinkler use, check the required pressure and flow, outlet size, available water and filtration before choosing a pump.
Plan a water butt and rainwater setup | Browse the collection-only water butt range
