The ball cock is a faucet which is opened or closed by means of a ball floating on the surface of the water as it rises and falls in the vessel.
In the illustration, Fig. [592], to be seen below the principle of its operation may be discerned. The fall of water in the tank lowers the float and opens the valve (which has in this case a rubber seat) and a rise of water in the tank closes the valve, hence this ball float controls and maintains a constant water level in the tank.
Fig. 592.
The float is a hollow ball of copper attached to one end of a lever while the other end is pivoted by a pin through it and the side of the shell of the valve. The valve itself is held by a screw to the lever and resembles very much an inverted lever safety valve.
This principle of construction and operation is applied to many devices among which is that described on page 318 relating to pump receivers.
The apparatus constitutes an automatic arrangement for keeping the water at a certain height. It is useful in cisterns, water backs, boilers, etc., where the supply is constant, the demand intermittent.