A regulator used for controlling the supply of steam to heating coils in tanks, is shown in Fig. 137. It is operated by means of the unequal expansion of two different metal bars, a, which when heated to a certain temperature by water in the tank, b, open a small valve, c, in a water supply pipe, thus admitting the water pressure to the diaphragm valve, d. The pressure of water on the diaphragm closes the valve and thus cuts off the supply of steam from the coil. As soon as the temperature of water in the tank falls sufficiently, the metal bars contract, thus shutting off the supply of water from the diaphragm valve, which is opened by a spring and again admits steam to the coil.

Fig. 137