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the dry return system, the drip pipes should be connected to the return main by a loop falling below the return, thus forming a trap and preventing the steam from flowing directly into the return.

One-Pipe Circuit System. In this system the main supply is carried to the ceiling of the cellar and there makes a complete circuit of the building at a downward pitch connecting again with the boiler below the water line, Fig. 81. From this circulation pipe, single risers are taken to the radiators, and the condensation flows back through the same pipes to the circulation pipe and is

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carried along with the steam and returned to the boiler. This circulation pipe should be of large size with a good pitch all the way.

In all single-pipe systems the piping must be larger than in the double-pipe systems, as the steam and the returning water are flowing through the pipes in opposite directions at the same time. This may be obviated by running a single riser to the top of the building where it branches out to supply the different radiators by separate pipes run back to the basement. In this case the steam and water flow in the same direction. For large work this method is often used.

Radiators. The form of steam radiator in general use is the cast-iron radiator, Fig. 82. It consists of a series of loops connected at the bottom; the steam, entering at one end, forces the air out of the valve placed about midway of the last section. The two end sections are of the same internal pattern as the others but are cast with legs.

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Fig. 82. Typical Cast-
Iron Radiator

Courtesy of American Radiator Company, Chicago

Pipe radiators, Fig. 83, are often used and, where design is not an object, the use of circulation coils of piping may be permitted.

Valves and Connections. Careful examination should be made of the valves and pipe connections to see that they are efficient and properly applied. Many styles of valves are available, and only well-known or well-tested patterns should be allowed. Of air valves for steam radiators the simplest form is the "petcock", a screw valve operated by hand, Fig. 84; but there are several forms of automatic valves on the market which allow the escape

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of cold air from the pipes but are instantly closed when the steam reaches them. This is accomplished by the expansion of a metal part which closes the orifice.

Fig. 84. Typical Air Valve

Boilers. Many of the ordinary types of steam boilers are used for steam heating, and in addition to these there is a cast-iron sectional boiler which is used for dwelling houses to a great extent, Fig. 85. The main thing is to select some well-known type and to see that it is carefully set, with all attachments, which will usually be described in the contracts. Details of Installation. This method of direct radiation lacks the advantage of the introduction of fresh air into the house, but, if care is taken to provide for that by other means we shall find the system desirable because it is economical and positive in its action. The important points to be watched are that heater pipes and radiators are amply large, and that the radiators are well placed and supplied by carefully

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graded pipes, tightly and neatly connected. Cellar pipes should be covered with some of the patented sectional pipe coverings, and radiators and all pipes which are exposed to view may be coated with bronze of a desired color. Where pipes pass through floors or partitions they should be protected by sleeves three-quarters of an inch larger than the pipes, and collars should be neatly

Fig. 85. Ideal Sectional 36-Inch Steam Boiler Courtesy of American Radiator Company, Chicago

placed around them at the floor and ceiling, or on each side of the partition.

Indirect Steam Heating. Other methods of heating are by indirect steam, indirect hot water, and a combination of hot air and

steam, and the same general principles will apply to these methods as to those which have been considered. The indirect application of steam or hot water is the system by which fresh air is brought to each register, after being heated by passing over a coil of steam or hot-water pipes, and while it is the most satisfactory of all means of heating, the expense of installation and maintenance is a bar to its employment for ordinary country or suburban house heating.

Vacuum Heating. A development of steam heating known as vacuum heating is a system suitable for large houses. It consists in installing in the basement of the house a vacuum pump operated automatically by town water pressure or by an electric motor. This pump, automatically controlled by the pressure in the pipes, removes the air from the pipes and radiators through automatic valves connected by a small pipe with the pump, allowing the steam to fill the system the instant it is turned on. This produces a prompt action throughout the whole system and thus effects a saving in fuel with less attention.

HOT-WATER HEATING

Another method of heating is by a similar application of direct hot-water radiation. This consists in circulating hot water through radiators placed in the rooms as in the case of direct steam heating. The hot water is conducted from the main heater in the cellar through the pipes and radiators, and the air is warmed by the direct radiation from these sources. The principle of this circulation is found in the difference in density and volume between hot and cold water. Water is at its greatest density at about 39 degrees Fahrenheit. When heated, its density decreases and its volume increases, so that as soon as the fire in the boiler is started the circulation begins; the water becomes lighter and flows up through the pipes, the radiators giving off its heat until, becoming colder and heavier, it flows back through the return pipes to the heater. This process is continuous as long as any heat is applied to the water in the boiler, the velocity of flow depending upon the difference in temperature between the supply and return, and the height of the radiators above the boiler.

Piping. The system of hot-water piping is that required for a free circulation of water from the heater to the radiators and

back to the heater again. The supply pipe is taken off at the top of the heater, and main and branches are run with an incline upward,

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VENT PIPE

OVER-FLOW

the return pipes being parallel to these and connected with the bottom of the heater. Risers are taken off the tops of the mains, and return pipes are connected with the return mains in the same manner, Fig. 86. As this system depends upon the force of gravity to keep up its circulation, an expansion tank, Fig. 87, must be provided, high enough above the highest radiator to insure free circulation, and the pipes ought to be run so that any radiator may be shut off without interfering with the general circulation. This tank should be

supplied with a glass gage and an

TER LINE

-WATER GLASS

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CONNECTIONS FROM SYSTEM

Fig. 87. Expansion Tank

overflow to some convenient place, and an open vent pipe should be taken from the top. The connection from the heating system enters

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