There are a couple of examples of the float valves that are used in plumbing installations. Their operation is slightly different but ultimately achieve the same result.The Portsmouth Float valve:This quite a common fit within the UK and has the other name of The Portsmouth Piston. Manufactured in Brass and very tough, this valve opens and closes using a cylindrical shaped plug moving backwards and forwards inside a horizontal chamber. Once the ball float sits in the ‘up’ position, the opposite end of the float arm moves the plug along its chamber. This has the result of pressing a rubber disc at the end of the plug hard up against the water inlet nozzle which closes off the water. A Westcombe Park Plumber fits this valve. With the ball float is in the ‘down’ position, the float arm retracts the plug back along its chamber, with the result that the rubber disc at the end of the plug moves away from the water inlet nozzle. This lets the water flow into the cisternNOTE:The Croydon valve works along similar lines, only the plug moves vertically not horizontally. Both types of valves are serviced by cleaning the piston and/or replacing the rubber disc. Diaphragm Float Valve:This ball or float valve is made of plastic and rubber. Its operation is much the same as the common brass valve. The float is lifted up and down by the level of the water. The business part of the arm, is such that when the water rises, a plastic piston will push against the rubber window or diaphragm, and the rubber disc on the reverse side of the diaphragm pushes against the water inlet nozzle and cuts off the water. Westcombe Park Plumbers know how these valves work. As the water level falls, so does the float. This stops the pressure on the diaphragm and water flows.