Can anyone tell me how the ball valve system on these toilet cisterns work. I have never seen a ball valve system like this. It appears to have a float which has air trapped inside as the water rises with a rod connector attached to the float going down to the base of the unit. If you take the float off and allow the water to come into the unit, pulling the rod up should in theory stop water but does not. Re-attach float water stops at required height. Does anyone know the theory behind this and how it works?