Flow control valve for water heater - has piston with circumferential ridges to prevent build up of scale

摘要

A flow control valve for a water heater consists of a piston (2) attached by a rod (11) to a diaphragm (7). A spring (4) acts on the diaphragm (7) so that the piston (2) is kept in the valve open position. The upper surface of the diaphragm (7) is connected to the venturi (1) so that the depression due to the velocity of the water lifts the diaphragm (7) upwards and tends to close the valve. The piston (2) slides in a tubular guide (8). The piston (2) is provided with circumferential ridges (9) which prevent any tendency of the piston 2) to bind in the guide due to the build-up of scale deposited by the water. Any scale which is deposited is easily rubbed off by the motion of the piston.