The high flow rate of the valve needs to be seen to be believed. The 50mm Unpowered Gravity-Feed Smart Irrigation Valve with an inlet pressure of 3 metres head (30 kPa) can deliver 3.5 litres per second. The valve can also operate at almost zero pressure.
 
Two containers are used with the inner container floating on water in the outer container. The swing check valve is mounted inside the inner container. An adjustable control dripper is connected to the outlet  of the valve so that, during the irrigation event, it drips water into the outer container via the lid of the inner container. During the irrigation event, the water level in the outer container rises, and when water level reaches the high level the swing check valve closes and the irrigation stops automatically. A polyester cover allows water to wick from inside the outer container to outside the outer container to evaporate. Between irrigation events, the water level falls as water wicks to the outside of the outer container and evaporates. When the water level reaches the low level, the swing check valve opens and the irrigation starts automatically. 
 
The irrigation scheduling responds automatically to onsite evaporation and rainfall. The rate at which the water level in the outer container falls depends on the onsite evaporation rate. When it rains, water collects on the lid of the inner container and drains via a drain tube to the outer container. The rain that has entered the outer container between irrigation events must evaporate before the next irrigation event can commence.
 
KEY FEATURES
Unpowered (no batteries, no wires, no solar panels, no electronics, no computers, and no WiFi)
No irrigation controller required
Water supply pressure can be almost zero
Very high flow rate
Uses NPC (non pressure compensating) drippers.
Use the adjustable control dripper to adjust the dripper discharge
Adjust the length of the polyester skirt to adjust the interval between irrigation events
Responds automatically to onsite evaporation and rainfall
The irrigation frequency increases significantly during a heat wave
When it rains, water enters the outer container and delays the start of the next irrigation event
Can be used for furrow irrigation
Simple, unpowered, and low tech, and therefore fewer things can go wrong
Leave your irrigation application unattended for weeks on end