An apparatus used to regulate the drafts of a water heater is shown in Fig. 136. It consists of a chamber, a, en-closed in a casting, d, with an annular space between them for water to circulate through. The inner chamber is connected by means of a pipe, c, to a diaphragm in valve, d, which is fitted with a lever and chain, so that any movement of the lever will open or close the dampers. The regulator is attached to the flow pipe from a heater, as shown in the illustration. The operation of the apparatus is as follows: The inner chamber is partly filled with water through the plugged connection, e, and the plug screwed in to prevent the escape of water or steam. The water in the inner chamber is under atmospheric pressure, which boils at 212 degrees Fahr., while the water in the heater is under an additional pressure that prevents it boiling at the same temperature as that in the chamber; hence, when the temperature of the water in the heater rises above 212 degrees Fahr. it will cause the water in the chamber to generate steam-, which presses the water against the diaphragm of the valve, d, thereby depressing the lever and closing the dampers. The fire is at once checked and no steam can form in the hot water tank, as the boiling point for the corresponding pressure has not been reached. When the temperature of the water in the heater falls below 212 degrees Fahr. the steam in the chamber condenses and pressure is released from the diaphragm, which immediately settles back into place, thus opening the dampers.

Fig. 136