A pump is chosen by two numbers: the flow you need (m³/h) and the total head it must overcome (meters) — not by horsepower. Get those right, match the pump type, and you avoid the classic mistakes: a pump that moves plenty of water but can’t push it high enough, or one far bigger than the task needs. This guide gives you the method, the formulas kept simple, and the traps.
The two numbers that matter
Flow rate (Q)
Volume of water per unit time — m³/h or L/s. This is “how much water, how fast,” and it’s set by your task: irrigating a given area, draining a pit within a deadline, filling a tank in an hour.
Total head (H)
The total resistance the pump has to work against, expressed in meters. It is the sum of three parts:
- Static head — the vertical lift from the water source up to the discharge point.
- Friction loss — resistance inside the pipe and fittings. Longer runs and narrower pipe add a lot of friction.
- Pressure head — any pressure required at the outlet, e.g. for sprinklers or a nozzle.
Add the three together; that is the head your pump must deliver at your required flow.
Don’t overlook suction lift
Atmospheric pressure limits how high a pump can pull water up to itself. In practice that’s about 7–8 m at sea level, and less at altitude — a highland site loses roughly a meter of usable suction for every 1,000 m of elevation, which surprises crews who moved a pump that “worked fine” at the coast. If the pump sits well above the water surface, choose a self-priming pump (or fit a foot valve) and keep the suction side short and wide to minimize losses.
Match the pump type to the job
| Pump type | Best for |
|---|---|
| Standard centrifugal | High flow, low-to-moderate head — irrigation, water transfer, drainage |
| High-pressure / multistage | Moderate flow, high head — tall lifts, long-distance delivery, sprinkler or boosting pressure |
HTX offers both standard and high-pressure diesel water pumps — compare them in the water pump catalog. The right family depends on whether your job is dominated by flow or by head.
Diesel vs electric drive
A diesel pump is the choice for off-grid, remote, or portable work, and anywhere grid power is unreliable — common in agriculture, construction and mining. Choose electric only where stable mains power is already present. Remember that a diesel pump is a diesel engine: it needs the same oil-and-filter care as any other, and it loses output at altitude like any other — the same derating rules from our altitude derating guide apply to the engine driving your pump.
A worked example
Irrigating from a river to a field: the field inlet sits 12 m above the river, the pipe run is 150 m of mid-size pipe (adds roughly 4–6 m of friction at the target flow), and the sprinklers need about 15 m of pressure head.
- Total head H ≈ 12 + 5 + 15 = ~32 m at the required flow.
- A standard centrifugal pump that delivers your Q at 32 m — with the duty point sitting in the middle of its curve, not at the ragged end — is the right machine.
- If the lift were 40 m and the line 500 m, the head would dominate: that’s high-pressure pump territory.
A five-step method
- Find the required flow (Q) from the task.
- Add up total head (H) = static lift + friction loss + outlet pressure.
- Read the pump curve — the pump must deliver Q at H (its “duty point”), ideally near its best-efficiency point, not at the far end of the curve.
- Add margin for pipe ageing and future demand.
- Check suction lift and pipe diameter — undersized pipe quietly destroys head, so don’t pinch it to save cost.
The mistakes that cost the most
- Buying by horsepower. Two pumps with the same engine can have completely different curves.
- Ignoring friction. A long, thin delivery line can eat more head than the vertical lift itself.
- Suction lift at altitude. The 7–8 m sea-level rule shrinks with elevation — plan the pump position accordingly.
- Running at the end of the curve. A pump forced far from its best-efficiency point wears fast and delivers poorly.
Send us your flow, your lift, and a rough pipe layout, and our team will recommend the right HTX pump and drive. Request a quote or message us on WhatsApp — we reply within 24 business hours.