The Unpowered Terracotta Valve is suitable for automatic sprinkler irrigation or drip irrigation. The valve operates with water supply pressure in the range 10 kPa to 800 kPa. The interval between irrigation events is automatically controlled by the on-site prevailing weather conditions (namely, evaporation and rainfall).
 
Terracotta is porous and so the water level in the pot falls as water seeps through the pot. A float inside the pot floats on the water. When the water level reaches the low level, a magnet inside the float activates the valve so that the valve opens and the irrigation starts. During the irrigation event a control dripper drips water into the pot and the water level rises. When the water level reaches the high level, the magnet inside the float disengages from the valve so that the valve closes and the irrigation stops.
 
Position the Unpowered Terracotta Valve in a suitable location in your garden so that the evaporation matches the evaporation at your plants. 
 
During an irrigation event, the control dripper replaces the water that has evaporated since the previous irrigation event. This volume is called the control volume. The Unpowered Terrcotta Valve has a control volume between 110 ml and 385 ml. 
 
Key features
Unpowered (no batteries, no solar panels, no electronics, no computers, and no WiFi)
Water supply pressure 10 kPa to 800 kPa
Half inch inlet and outlet
Use for sprinkler irrigation or drip irrigation
Use for gravity feed or pressurised irrigation 
Adjust the water usage rate by adjusting the control dripper
Adjust the interval between irrigation events by adjusting the float
Responds automatically to on-site evaporation and rainfall
The irrigation frequency increases significantly during a heat wave
Irrigate directly from a rainwater tank without using a pump
Water in the terracotta pot is protected from debris, algae, mosquitoes and thirsty animals
Simple, unpowered, and low tech, and therefore fewer things can go wrong
Leave your irrigation application unattended for months on end