Diaphragm Valve:This type of valve has been used in a domestic plumbing situation for many years. They are normally made by connecting a ball of plastic or rubber to an extended metal arm. The ball, then lifts and lowers as the water rises, resulting in the opening and closing of the inlet water supply valve. As the water rises a piston made of plastic pushes against a rubber window or diaphragm, this pushes on a rubber disc on the other side of the diaphragm and is forced against the water inlet nozzle to cut off the water. Abbey Wood Plumbers know how these valves operate and can fix them. When the water level drops, the float falls, with the effect that the other end of the arm will stop pressing against the diaphragm and the water flows through the nozzle.Portsmouth Valve:Constructed of brass and pretty much indestructible, this type of valve is really popular and used frequently. Its operation uses a cylindrical plug that moves back and forth in a horizontal chamber. Once its float is in the ‘up’ position, the opposite end of its arm moves the plug along the chamber. This results in a rubber disc at the end of the plug pressing hard against the water inlet nozzle and stopping the water flow. A Thamesmead Plumber fits this type of valve and can locate plumbing problems. Now, when the float is in the ‘down’ position, the arm drags the plug backwards through the chamber. This results in the same rubber disc located at the end of the plug pulling away from the water inlet nozzle, and opening up the flow of water to fill the cistern ready for flushing again. Note:A third valve called a Croydon valve operates in a similar way. The only difference is the plug moves in a vertical plane and not horizontal. This valve is not really used.