An irrigation pump enquiry should specify the flow required at the system’s total dynamic head. Maximum free-flow capacity and maximum head are not normally the same operating point. Give the supplier a complete water-system brief rather than combining two attractive catalogue numbers into an assumed performance.
Flow and head must share an operating point
Before you approve the quotation: Send the designer’s system duty and seasonal conditions with the enquiry. Require the selected point on the actual pump curve plus suction, drive and control limits. The input-power example explains the duty; final equipment selection needs the complete system assessment.
Compare the working alternatives
| Decision | Alternative A | Alternative B | Buyer’s evidence |
|---|---|---|---|
| Flow basis | Maximum catalogue flow | Required flow at system duty | Irrigation designer brief |
| Head basis | Vertical lift alone | Total relevant head and pressure losses | System calculation and measured inputs |
| Pump comparison | Separate maxima combined | Pump curve at the required operating point | Manufacturer selection data |
| Water source | Water appears available | Relevant level, yield and permissions confirmed | Responsible local assessment |
| Installation | Pump supplied alone | Drive, controls and interfaces coordinated | Qualified system design and commissioning |
Where the specification can go wrong
Have the responsible irrigation designer establish crop-water requirements, available supply, static levels, pipework, delivery conditions and relevant seasonal variation. The pump supplier needs the system duty, not only a field area. Water-source permissions, available yield and destination requirements must be confirmed by the responsible local parties.
Include losses and required delivery pressure on a consistent head basis. The actual duty point depends on the pump and system together, and can change as levels or components change. Suction conditions, drive power, control and operating limits require competent selection. A simple power calculation helps explain inputs but cannot replace the manufacturer’s curve and application assessment.
A worked buying example
Illustrative assumptions; not a supplier quotation, an approved design or a machine rating.
Assume 25 m static lift, 8 m friction loss and 12 m required delivery head: total head is 45 m at the stated flow. For the same illustrative duty of 12 m³/hour at 45 m head, water density 1,000 kg/m³ and 50% overall efficiency, input power is about 2.94 kW. These assumptions do not select a pump; the real curve, conditions and complete installation must be assessed.
Put the decision in the purchase order
Issue the designer’s duty and system inputs to suppliers on one common basis. Require a selection showing the proposed pump’s operating point and relevant limitations. Identify who provides pipework, controls, power and commissioning. At acceptance, record the actual equipment and agreed measured evidence so a later change in water level, filters or delivery requirements prompts a system review rather than reliance on an unrelated maximum-flow label.
Questions to send with the enquiry
- What flow and total dynamic head has the irrigation designer established?
- What seasonal water levels, yield and local permissions apply?
- Where does the proposed duty lie on the actual pump curve?
- Who designs and commissions the complete drive, control and pipework system?
Send Auto From China your enquiry, including your destination, operating brief and the answers above. We can work with manufacturers to compare the relevant vehicle or machinery configuration and identify the items that still need written confirmation.
Technical references
- Grundfos: How to read a pump curve — Pump-curve interpretation; actual pump selection requires the complete duty, installation and applicable manufacturer data.
- FAO irrigation water management: Chapter 6, drip irrigation — Irrigation system and water-quality context; final crop, water and hydraulic design needs local assessment.