Supply tank.
The attic tank may be of wood or iron, and its capacity should be equal to the daily consumption of water. Its purpose, as already indicated, is to equalize the varying rates of consumption from hour to hour and between day and night. The minimum size of this tank would be such that the flow during the night would just fill the tank with an amount of water just sufficient for the day's needs. Of course, the additional supply entering the tank during the day would reduce the size somewhat, but the basis for computation given is not unreasonable.
Several accessories must be provided for such a tank. An overflow is essential, and this is best accomplished by carrying a pipe out through a hole in the roof. This must be ample in size, provided with a screen at the inside end, and be examined frequently to make sure that the overflow remains open. A light flap valve to keep out the cold in winter is also a desirable feature for the overflow pipe. The tank must be water-tight, and while it is possible to make a wooden tank water-tight, it is wiser to line a wooden tank with lead or sheet iron. The latter can be painted at intervals, so that it will not rust, and is safer than wood alone to prevent leakage.
Care must be taken to give sufficient strength to the wooden tank; it should never be made of less than two-inch stuff, and should not depend upon nails or screws alone for holding the sides together. Figure 56 shows a suitable way to put together such a tank. Certain firms that make windmills and agricultural implements generally can furnish wrought-iron tanks, warranted to be water-tight, of suitable size to go in an attic. Such a tank, as we have already said, should hold about five hundred gallons and should therefore be a cube four feet on a side or its equivalent. It needs to be very carefully placed in the house, or else its weight will cause the attic floor to sag. A tank of the size named will weigh a little more than two tons, and such a weight, unless special precautions are taken, cannot be placed in the middle of an attic floor without causing serious settlement, if not actual breaking through, of the floor.
Fig. 56.—Construction of a wooden tank.
A good way of placing such a tank is to nail the floor joists onto the bottom of the rafters, so that a truss is formed, and the box or tank is properly supported on the floor and also hung from the rafters by iron straps bolted both to tank and rafters. If possible, this tank should be placed directly over a partition carried through to the cellar, in which case no settlement is possible.
Main supply pipe.
The main supply pipe, except when pressure is very great, is most satisfactory when made of three-quarter-inch galvanized iron pipe. Even with a high pressure, half-inch pipe is unsatisfactory because of the great velocity with which the water comes from the faucets and because the high pressure causes the packing in the faucets to wear out rapidly. This three-quarter-inch pipe should have a stop-and-waste, as it is called, just inside the cellar wall, so that if the house is not occupied at any time, the valve may be shut and the water in the pipes drawn off, to prevent possible freezing. The pipe should never be carried directly in front of a window or along the sill of the building unless protected by some kind of wrapping. The laterals and the different fixtures are taken off from this main supply pipe as it rises through the house, and the pipe is capped at the top.
Hot-water circulation.