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This site sets out to answer two precise questions: how much water will this pump give in my system? and how many sprinklers can my tap supply? Doing that honestly means saying where the numbers come from and where our knowledge ends.

Pump data

• Every value for a pump comes from a manufacturer’s document: manual, data sheet or catalogue. Next to it is the link and the date on which we read it.
• When the manufacturer publishes points on the curve (for example “2,900 l/h at 5 m”), we use them as they are. We do not read values off graphs by eye.
• When it publishes only maximum flow and maximum head, we join the two points with a straight line and flag it as an indicative estimate: it rests on these two values only and is not a confirmation. A real curve is usually not a straight line.
• If two documents from the same manufacturer disagree, we report it and do not pick the more favourable value.

Calculations

• Pipe losses: Darcy-Weisbach equation; friction factor from the Colebrook-White equation, solved by iteration starting from the Swamee and Jain formula [3].
• Water: at 20 °C, kinematic viscosity from a published table [1]; density 1,000 kg/m³, about 0.2% above the real value and negligible compared with the other uncertainties.
• Pipes: roughness of 0.007 mm, the highest value for smooth plastic pipes [2].
• Duty point: found where the pump curve meets the system curve, never extrapolating beyond the documented points.
• Checks: the calculations are checked by automated tests against known solutions: the Hagen-Poiseuille formula in laminar flow, the Colebrook-White equation in turbulent flow, duty points that can be solved by hand.

Irrigation

• Data: nozzle flow and radius, maximum dripline lengths and operating pressures come from the manufacturers’ tables (Rain Bird, Toro, Claber, Irritec, Soaplast). We interpolate between rows and never extrapolate.
• Zones: pipe losses are calculated section by section between one sprinkler and the next [65], each at its own pressure according to the table. With identical outlets the result matches the Christiansen factor [66].
• Tap: from the static pressure (with no water flowing) and from the bucket test we estimate the pressure available at each flow, with losses proportional to the flow raised to the power 1.75 [65][67]. This is our own model, not a measurement.
• Precipitation rate: from flow and spacing, as in the Rain Bird design guide [68]. It reproduces the declared values of 12 nozzles out of 13 to within 3%; for the R-VAN18 at 180° the difference is 6%, because Rain Bird declares a single nominal value for the family.
• Below 0.5 bar no manufacturer we have read publishes data: for a gravity-fed tank we make no estimates.

What we do not know yet

• We have not yet measured pumps, sprinklers or driplines ourselves. The curves are the declared ones, which usually apply to a new unit under the manufacturer’s test conditions.
• We do not know the variation between units of the same model.
• Fittings, filters, valves and the suction hose are not in the calculation: the real flow will be lower than the estimate.

If the site proves useful, the next step is a test bench with a pressure gauge, a control valve and water weighing, to publish measured curves with raw data and uncertainties.

How we choose the order

Pumps and sprinklers are ranked by what they deliver in your system (estimated flow, sprinklers per zone), never by commission. Some links to shops may be affiliate links: we explain this in the disclosure.