Other valves employ an expansion plug and in addition contain a light metal float open at the bottom. Air valves frequently give annoyance by leaking, due to a sudden rush of water in the radiator which is forced into the air valve by the steam pressure. The light float is intended to overcome this difficulty as a sudden rush of water will raise the float and temporarily close the outlet of the valve. When the water recedes the float will drop and open the outlet to allow the escape of the air.

29. Q. What condition should be guarded against in using automatic air valves?

A. When air valves are placed on new work or a heating system that has not been effectually cleaned of dirt and scum, the movable parts of the valve and the small inlet and exhaust outlet become clogged and render the valve inoperative.

Q. How may this condition be avoided?

A. Automatic air valves should not be placed on a heating system until it has been in operation for a period of a week or ten days and has been effectually cleaned of oil and dirt. Common compression valves should be used during this period.

31. Q. What other cause ruins the efficiency of automatic air valves?

A.

Automatic air valves, particularly those of the expansion post type, which are adjustable with a screw driver, are frequently ruined by improper adjustment or by excessive pressure.

Certain types of expansion post valves are so delicately sensitive that when adjusted to close, at a slight pressure of steam, are ruined by being subjected to a high temperature of the steam during a period when a considerable pressure is developed for testing piping or for blowing off the boiler. The carbon post buckles with the expansion due to the high temperature and will never regain its original shape and efficiency.

32. Q. What remedy is there for this condition?

A. Should the valves be in position during this period they should be let open, and their adjustment should be deferred until normal conditions of pressure and temperature prevail.

33. Q. What is the meaning of the term "Syphon air valve"? A. Under certain conditions, due to the method of piping used or to the manner of operating the heating system, there is frequently a tendency for the water in a radiator to surge into the air valve. In some air valves a slight vacuum will hold this water in suspension and thus render the valve inoperative.

Some styles of air valves are provided with a syphon which drains this water back into the radiator. Fig. 112 shows a cut away view of the No. 1 Hoffman Syphon automatic air valve; the illustration indicates clearly the construction of the valve and syphon. It is of all metal construction and is non-adjustable. A valve of this type cannot be tampered with or improperly ad(12) VALVE PORT

Fig. 112.-No. 1 Hoffman Syphon Air Valve.

justed by anyone. Various makes of air valves have a syphon attachment and are also non-adjustable.

34. Q. What vacuum features are sometimes applied to automatic air valves?

A. The condensation of steam in a radiator, when the system. of piping, supply valves, and other fixtures are tight, will produce a vacuum which will hold for a considerable period after the steam pressure has been removed from the radiator. The ordinary type of automatic air valve is open to the pressure of the atmosphere

at all times when not filled with steam. Air valves are to be had which will freely exhaust the air, but which are at all times closed to the pressure of the atmosphere; such valves are commonly called "Vacuum Air Valves."

35. Q. What is meant by the term "Free venting air valves"?

A. Air valves having an extra large inlet and exhaust port are commonly known as "free venting" valves. Air valves of this

Air Valve.

type are used on the end of large mains, on stacks of radiation used for hot blast heating and at other points on a heating system where it is desired to exhaust the air quickly. The Hoffman No. 5 (Fig. 113) and the Hoffman No. 6 (Fig. 114) are representative of this class of valves, the latter style possessing the vacuum features already alluded to.

Air valves of this type, as well as the smaller sizes, may be had in a variety of styles and types.

148

MODERN METHODS OF HEATING

A large share of the many troubles experienced by the steam and hot water fitter, in the installation of steam and hot water apparatus for heating, are due to the presence of air in the heating system.

Air forming in pockets in various parts of the piping system either blocks the circulation entirely, or reduces the efficiency of the apparatus by reducing the effective area of the pipe or radiating surface at the point where the air pocket occurs.

Radiators and coils are often partially air bound. In a steamheating system this is due to the steam reaching and closing the automatic air valve before the air is entirely exhausted from the coil or radiator.

Steam and air, being of different densities, will not mix. As the steam enters a pipe or radiator which is filled with air this air is compressed or pocketed in a section of the piping or radiating surface. The steam cannot enter an air bound pipe or radiator, and, therefore, the square feet of actual radiating surface is reduced and the efficiency of the apparatus is otherwise greatly impaired.

Air has been called the arch enemy of the steam fitter, as it is the one agency against which he must continually fight in order to meet success or in order to install successfully working heating systems.

The development, during the last twenty-five years, of improved methods of heating has resulted in the designing of many appliances for ridding the heating system of air and the troubles due to it. Since the year 1882 heating engineers, contracting fitters and others have been interested in the problem of circulating steam at or below the pressure of the atmosphere. They have recognized the loss sustained by allowing the exhaust from engines, pumps, etc., to be wasted, and have evolved a method of utilizing it to the best advantage in the heating system. They have perfected systems of heating which utilize exhaust steam most economically and also systems of a more simple type for use in residences as well as buildings of greater size and importance.

These systems are so varied in character that it is extremely difficult to classify them. A steam heating system that makes use of a pump, exhauster, or other device to exhaust the air, and which

operates below the pressure of the atmosphere, is called a mechanical vacuum system. A steam heating system which operates at atmospheric pressure, or a few ounces above the pressure of the atmosphere, is called a vapor or atmospheric system, and some vapor systems by the use of certain devices are so designed as to operate a portion of the time under a partial vacuum. Such systems are known as vapor-vacuum or vacuum-vapor systems. Other systems are designed to operate at times as a pressure system, a vapor system, or a vacuum system, and these systems are frequently spoken of as a three-in-one system.

To many of the modern modified heating systems are given names which designate the name of the man who patented the system or the concern who manufacture it. Among these systems are the Webster Modulation System, the Dunham Home System, and others.

In treating of the subject of modified heating systems-vacuum, vapor, or a combination of both-we shall illustrate and describe some systems representative of each class and, by means of questions and answers, call attention to the character of the special appliances used and the more important details of installation.

With a knowledge of the principles of vacuum and vapor heating and an understanding of what is to be accomplished by their use it will be seen that the methods adopted are neither complex nor difficult.

I. Q. What is meant by a vacuum?

A. The definition given by Webster states that a vacuum is a space absolutely empty or void of matter.

2. Q. Is a bottle empty in the sense that we remove from it its visible contents?

A. No. The bottle is erroneously called empty, but it is not for the reason that when the visible contents are removed from a vessel it immediately refills with air, an invisible gas containing more or less water. This gas permeates or is forced into every opening or crevice in everything upon the face of the earth by reason of the weight of the atmosphere.

3. Q. How can a vacuum be produced and maintained?

A. By exhausting the air from the interior of a vessel either by the force of expansion of heat or steam or by employing some mechanical device, and then closing or sealing the vessel against the return of the air, or removing from it the pressure of the atmosphere.