Blumat Single 5"

Each Tropf Blumat is filled with water and voided of air prior to being connected to a pressurized line (pressure from gravity-feed is adequate). The water inside the Blumat is in a completely sealed environment.  The only exposure it has is through the pores in the ceramic cone.  
 
As soil surrounding the cone dries
It pulls on the moisture inside the cone through osmotic pressure.  Since this is a sealed environment and the pressure cannot equalize, this pulls on a plastic diaphragm in the top of the Blumat.  
When the diaphragm is pulled down, it allows an irrigation tube running through the top of the valve of the Blumat to open and emit moisture.  It does this very gradually.
As the water is emitted through the Blumat, the moisture is gradually restored to the soil surrounding the porous ceramic. 
This relieves the pressure difference between the chamber inside the Blumat and the surrounding soil. This stops pulling on the diaphragm, and the diaphragm restores its former position of pinching the irrigation tubing shut.
Allowing each plant to determine its own watering schedule.