Vacuum and Vapor Heating

VACUUM AND VAPOR HEATING Properly to understand vacuum and vapor heating, it is necessary not only to have knowledge of the meaning and applications of these terms, but also to understand the reasons for the application of the principles to heating apparatus.

In all standard dictionaries a vacuum is defined as an "empty space." We speak of a bottle from which. the contents have been re moved as being empty, and, according to the dictionary definition, this condition would therefore seem to be a vacuum. This, however, is not true, for, while the visible contents have been extracted from the bottle, the space formerly occupied by these contents has simply been filled with another and invisible volume— the vaporous gas we call air. This supply of air is under a pressure of 14.7 pounds, the same as the outside atmosphere surrounding the bottle; and this force we call atmospheric pressure.

If an attempt is made to refill the bottle without providing a vent or opening for this inner air to escape, it will be found impossible to refill it.

What causes atmospheric pressure ? The earth is surrounded by a belt of elastic gas many miles thick. This air, containing more or less moisture in the form of vapor of water, is denser nearer to the earth than at high alti tudes. Like all other substances, air has weight, because of the attraction of gravity. It exerts a pressure upon all objects upon the earth to the extent of 14.7 pounds per square inch at sea level. In other words, the atmospheric pressure upon a surface is simply equivalent to the weight of the column of air pressing upon that surface. On of air being a fluid, the pressure is exerted equally in all directions. The higher we ascend in the air, the less the degree of this pressure. Water in an open vessel will boil at sea-level when it has been heated to a temperature of 212° F.; at an alti tude of about two miles above sea-level, the same supply of water will boil or vaporize at a temperature of approximately 190° F.

Now, returning again to the illustrations afforded by a consideration of the water- and air-filled bottle, let the air itself be extracted from the bottle. The bottle will then be, as we

say, under a vacuum, and a vacuum exerts a pull upon the opening in the neck of the bottle.

What has the information gained from this discussion to do with the heating question'? Let us see. Water, when vaporized or converted into the gaseous form we call "steam," occupies a space about 1,700 times as great as it did in its original liquid state; in other words, one cubic inch of water, when vaporized, will be pro ductive of 1,700 cubic inches of steam. Fill a radiator with steam, and then condense the supply. It will occupy as water but one sixteen hundred and ninety-ninth part of the space it occupied as steam, the remainder of the space being filled with air sucked into the radiator through the air-valve, and this volume of air has the pressure of the atmosphere. In circulating steam, it is necessary to overcome this pressure, and to drive the air from the radiator through the valve before the radiator can again be filled with steam. Air is the arch enemy of the heat ing contractor.

Vacuum heating provides a method for keeping all air out of a heating system, and, at the same time, for exerting a pull, by means of a pump or other device, upon the return ends of all units of radiation, thereby allowing and facilitating the flow of steam to all parts of the apparatus without pressure.

Vacuum Heating Systems. There are two classes of this kind of heating—first, those making use of a pump or other mechanical device for creating the vacuum; and second, non-mechanical systems which are used in con nection with the ordinary methods of steam piping for residence work. Among the com mercial systems in the former class may be named the Webster, the Paul, and the Van Auken systems; among those in the latter division are the Trane, the K-M-C (Morgan), the Gorton, the Ryan, the Moline, and the Dunham. All are designed to accomplish the same purpose—namely, that of circulating steam or vapor through a heating system at a pressure equal to or below that of the atmo phere.