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Emitters

The emitter choice is critical in a low-pressure setup.

In a pressurized irrigation system, the available pressure is usually high enough to support many common emitters fed from the same main line. In a gravity-fed system, the available pressure is much lower, so the amount of emitters that can be supplied by one main line is usually lower and must be planned more carefully.

For example, if the water container is elevated by about 1 meter, the available pressure is about 0.1 bar.

At around 0.1 bar, OpenValve's maximum flow rate is 6 liters per minute. How many plants can be watered with this flow rate depends strongly on the emitters.

For example, if OpenValve provides approximately 6 L/min at 0.1 bar (1 m water head):

  • If each emitter outputs 1 liter per minute, a maximum of 6 emitters can be used.
  • If each emitter outputs 0.1 liters per minute, a maximum of 60 emitters can be used.
  • If each emitter outputs 0.01 liters per minute, a maximum of 600 emitters can be used.

There is one important trade-off to keep in mind: the smaller the emitter outlet, the more susceptible it is to clogging, especially when using unfiltered rainwater that may contain dirt or algae. Very small emitters may therefore require an additional filter upstream.

tip

The smaller the emitters, the better the water must be filtered.

Gravity Nozzle​

Because there are only few emitters available that work well with very low pressures, I designed an emitter specifically for this use case: The Gravity Nozzle.

It fits common micro tubing sizes such as 1/4" hose or 4 × 6 mm tubing, is infinitely adjustable from 0-400 ml/min at 0.1 bar, and can be easily 3D printed without supports.

Its comparatively large adjustable outlet also makes it suitable for use with unfiltered rainwater, while still allowing the flow rate to be adjusted individually for plants with different watering needs.