This section is from the book "American Plumbing Practice", by The Engineering Record. Also available from Amazon: Plumbing: A working manual of American plumbing practice.
Figure 4 is a view of one of the four roof tanks which, with a united capacity of about 60,000 gallons, store the house water supply. The tanks are built of angle and plate iron, and are supported about 3 feet above the floor on broad wooden frames A A, which rest on the tops of the iron floor beams. KKK are 6-inch iron beams under the tank. They are tied together by the ¾- inch rods L L.
D is the 2-inch pipe which serves both for the house-supply riser and the pump-delivery riser. It is connected to the tank by branch C, in which a check valve, not here shown, permits the flow of water from the tank, but prevents any flow into it.
E is a branch to a cock F, for a roof supply, and G is an air chamber. H is 2-inch emptying pipe, and I is the 3-inch overflow discharging on the roof. The tanks are covered by galvanized-iron houses, just large enough to inclose them, and containing steam coils on two sides of the tanks to protect them from freezing.
Figure 5 is a view of the rear end of the hot-water tanks. A and B are 3-inch supplies from Fifty-ninth Street and Fifth Avenue respectively. They are connected to the header C, and have valves arranged so that either or both A or B can supply either or both tanks. D D D D are the tank connection pipes, made 2 inches in diameter, for convenience of tapping into the tanks, and put on in pairs to secure equivalent area of cross-section. E is the 3-inch hot-water header connected to the tanks by 2-inch branches F F F, and controlled by valves, so as to receive water from either or both tanks. Its 2-inch branches G and H, to different parts of the house, can be put in communication or separated by opening or closing valve J.
I is a 1½-inch special hot-water supply direct to the kitchen; K is a ½-inch drip pipe to empty various riser lines. Another direct house supply, not here shown, is taken from the opposite ends of the tanks.