Choose a pump from its duty point, not its motor size. Work out the flow you need and the total head at that flow, then pick the pump type that suits your water source and a model whose best efficiency point sits close to that duty.
Everything else, from materials to motor and controls, follows from the source, the water and the power supply.
Step one: define the duty
- Flow: the volume you need per hour or per second at the outlet.
- Static head: the vertical distance from the lowest pumping water level to the highest delivery point.
- Friction losses: the extra head lost in the pipe, bends, valves and filters at your flow.
- Outlet pressure: any pressure you need at the end, such as for sprinklers or drip lines.
- Total head: the sum of the last three, which is the figure you take to the pump curve.
Step two: match the source
A borehole needs a borewell submersible that fits its diameter. An open well or sump suits an openwell submersible. A shallow tank or canal suits a monoblock or coupled centrifugal pump, as long as the suction lift is short. The differences are set out in submersible, monoblock and centrifugal pumps compared.
Step three: check the water and the power
Water quality decides materials. Sandy water needs wear-resistant stages and sand-handling limits. Corrosive or saline water may need stainless steel or bronze parts instead of cast iron. Hot water needs a motor and seals rated for the temperature.
Power supply decides the motor. Confirm phase, voltage and frequency, and whether the supply is stable. A pump built for 50 Hz will not perform correctly on 60 Hz, as explained in pumps for 50 Hz and 60 Hz power. If the supply is solar, the pump and controller must be chosen together.
Step four: pick the model
Plot your duty point on the curves of shortlisted models. Choose one where the point falls near the best efficiency point and inside the range the maker recommends. If two models fit, the one with higher efficiency at your duty will usually cost less to run.
Think about how many hours a day the pump will run. A pump running long hours justifies a more efficient model and better materials, because running cost soon outweighs purchase cost.
Check that the motor is not overloaded if the head turns out lower than planned, because flow and power rise when head falls. Then add the controls: starter, protection panel, dry-run protection or a VFD. Our guide to reading a pump curve explains each line on the chart.
Next step
If you are importing pumps for resale, define a few duty points that cover most of your customers and build your range around them. We can turn that into a specification and find makers to match. Book a free sourcing review.