The unpowered valve inside the valve box has a 15mm inlet and outlet. 
The Unpowered 15mm Valve Box allows you to automatically irrigate you garden using gravity feed from an elevated rainwater tank without uisng  a pump and without power.
 
Installation instructions:
Install drip line (subsurface or surface, PC or NPC, drip tube or drip tape).
Replace a typical dripper with a subsurface clay pot. 
Connect the clay pot to an Unpowered Valve Box.
Connect the water supply to the inlet of the valve box (10 kPa to 800 kPa).
Connect the drip line irrigation system to the outlet of the valve box.
Connect a drip line dripper inside the valve box.
Fill the valve box with water until the float is partially covered.
Turn on the water supply and all your plants will be watered automatically without power.
 
The discharge from each dripper can be set to any value between 569 ml and 1223 ml.
If you use a pair of clay pots, you should use two drippers in the valve box and the discharge from each dripper can be set to any value between 285 ml and 612 ml.
Similarly, if you use three clay pots, you should use three drippers in the valve box and the discharge from each dripper can be set to any value between 160 ml and 408 ml.
 
The discharge from each dripper during an irrigation event is the same as the average on-demand discharge from a clay pot since the previous irrigation event.