—In Fig. 35 is illustrated another system of high-pressure hot-water heating that corresponds to the overhead system of steam heating. It differs from the high-pressure system already described in the method of distribution and in the radiator connections.
The flow pipe is taken to the attic and there joined to the expansion tank as a point of distribution. On the expansion tank is a safety valve set at 10 or more pounds pressure. The flow of the water is all downward toward the radiators. The circulation through the radiators is also different from the other plants described. The supply pipe joins directly to the return pipe and the connections to the radiators are made at the top and bottom of the same end. The circulation through the radiators in this case is due to the difference in gravitational effect between the hot and colder water at the top and bottom of the radiator. The system requires no air vents on the radiators as all air that might collect in the system goes up to the expansion tank. The safety valve on the expansion tank in this case is the common lever type. The overflow should empty into the sewer and be pitched to prevent any water being retained in the discharge pipe. If water should be retained in this pipe and should freeze, the system would become dangerous, because of the possibility of high pressures from a hot fire.
Fig. 35.—The overhead system of hot-water heating.
Expansion Tanks.
—Fig. 36 is a form of expansion tank in common use. It may be used for either the high-or low-pressure system. The body of the tank is made of galvanized iron and is made to stand a considerable amount of pressure. The gage-glass is attached at B, and the overflow at O. The pipe E connects the tank with the circulating system and D connects with the cold-water supply as a convenience for filling the system with water. The object in placing the stop-cock D near the expansion tank is to avoid overflowing the system in filling. The overflow pipe, as stated above, is most conveniently connected with the sewer, into which the water will run in case of an overflow, but the other methods shown are commonly used. There should be no valve in this pipe nor in the pipe E.
Fig. 36.—The expansion tank.
Fig. 37.—When the expansion tank of a hot-water heating system must be so located that it is apt to freeze, it must be piped as a radiator.