Emitter Flow & Dripper Discharge q = k·Hˣ

By the emitter discharge equation q = k × H^x, where q is the flow in litres per hour, H is the operating pressure, k is the emitter's discharge coefficient and x is its discharge exponent. The tool raises the pressure to the power x and multiplies by k to give the discharge at your operating pressure.

The exponent x measures how sensitive the emitter's flow is to pressure. An x near 1.0 means flow rises almost in step with pressure — a simple long-path or orifice emitter. An x near 0 means flow barely changes as pressure varies — a fully pressure-compensating emitter. The lower the x, the more uniform the discharge along a line with pressure differences.

A pressure-compensating (PC) emitter has a flexible diaphragm that throttles the flow path as pressure rises, holding the discharge nearly constant over a working pressure range. Its discharge exponent x is close to zero, often 0.0–0.2. PC emitters give uniform watering on long runs, sloping ground and undulating terrain where pressure varies along the lateral.

Orifice and long-path emitters usually have x around 0.5–0.7; turbulent-flow emitters around 0.5; and pressure-compensating emitters around 0.0–0.2. Manufacturers publish k and x for each model, or you can fit them from two flow-versus-pressure measurements. The lower the x, the flatter the flow curve.

Uniform discharge means every plant gets the same water, which drives even growth and efficient use. Pressure always drops along a lateral due to friction, and rises or falls with slope, so emitters at different points sit at different pressures. A low exponent keeps their flows close despite that, which is why PC emitters are chosen for long or sloping lines.

Use the manufacturer's recommended operating pressure, typically 0.5–1.5 bar (about 5–15 m of head) for drip emitters. Running below the range under-waters and can let emitters drain unevenly; running above wastes energy and, for non-PC emitters, over-applies. The tool lets you test the discharge across the range before you set the regulator.

Yes. Measure the discharge at two different pressures, then x = ln(q2/q1) ÷ ln(H2/H1), and k = q1 ÷ H1^x. With k and x in hand, this tool predicts the discharge at any pressure in the working range, which is handy when a catalogue value is missing or you want to verify an emitter in the field.

Yes — clogging from sediment, biofilm or precipitates raises the effective flow resistance and lowers discharge below the q = k·H^x curve, and it does so unevenly across emitters. The equation describes a clean emitter; declining or patchy flow in the field is a sign to flush the lines and check filtration. Regular maintenance keeps real flows close to the calculated value.

They are accurate for the k and x you enter, which are the manufacturer's published or field-fitted values. Real discharge varies a little with water temperature, manufacturing tolerance between emitters and clogging over time. Use the result for design and pressure setting, and verify with a catch test on a sample of emitters in the field.