Ballcock

A ballcock (also balltap or float valve) is a mechanism or machine for filling water tanks, such as those found in flush toilets, while avoiding overflow and (in the event of low water pressure) backflow. The modern ballcock was invented by José Antonio de Alzate y Ramírez, a Mexican priest and scientist, who described the device in 1790 in the Gaceta de Literatura Méxicana. The ballcock device was patented in 1797 for use in steam engines by Edmund Cartwright.

In its most basic form the ballcock consists of a valve connected to a hollow, sealed float by means of a lever mounted near the top of the tank. The float is often ball-shaped, hence the name ballcock. The valve is connected to the incoming water supply, and is opened and closed by the lever which has the float mounted on the end. When the water level rises, the float rises with it; once it rises to a pre-set level, the lever mechanism forces the valve closed and shuts off the water flow. This is an example of negative feedback and of proportional control.

An alternative to the traditional ballcock is the float cup, pioneered in 1957 by the Fluidmaster founder Adolf Schoepe, which is integrated with the tank's fill valve and so consumes less space. A later innovation, the floatless fill valve, designed for low-profile, low-flow toilet tanks, uses a pressure-sensing diaphragm mechanism instead of a float to control the inlet valve. Delay valves, which delay the filling until the level has dropped to a low level, avert short-cycling of the water supply.