The Unpowered Terracotta Valve with Booster 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. 
 
Connecting the booster to the terracotta pot boosts the control volume to between 1000 ml and 1825 ml. If the adjustable control dripper is replaced by one of the irrigation drippers, each of the drippers will discharge the control volume of water during the irrigation event. The irrigation frequency can be adjusted by adjusting the exposed surface area of the polyester cloth.
 
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
The booster allows the control volume to be set to any value between 1000 and 1825 mls
If the adjustable control dripper is replaced by one of the irrigation drippers, then each dripper in the irrigation application will deliver the control volume during the irrigation event
If the adjustable control dripper is replaced by two of the irrigation drippers, then each dripper in the irrigation application will deliver half the control volume during the irrigation event
The polyester cloth allows the interval between irrigation events to be adjusted by adjusting the exposed surface area of the polyester cloth
Provided the same drippers are used throughout the irrigation application (including the control dripper), the dripper discharge is independent of the water supply pressure
Irrigate directly from a rainwater tank without using a pump
Water in the terracotta pot and the booster are 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