This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Cold steam pipes expand approximately 1 inch in each 100 feet in length when low pressure steam is turned into them, so that in laying out a system of piping we must arrange it in such a manner that there will be sufficient "spring" or "give" to the pipes to prevent injurious strains. This is done by means of offsets and bends. In the case of larger pipes this simple method will not be sufficient, and swivel or slip joints must be used, to take up the expansion. The method of making up a swivel joint is shown in Fig. 52.
Any lengthening of the pipe A will be taken up by slight turning or swivel movements at the points B and C. A slip joint is shown in Fig. 53. The part c slides inside the shell d and is made steam tight by a stuffing box as shown. The pipes are connected at the flanges A and B.
When pipes pass through floors or partitions, the woodwork should be protected by galvanized iron sleeves having a diameter from 3/4 to 1 inch greater than the pipe. Fig. 54 shows a form of adjustable floor sleeve which may be lengthened or shortened to conform to the thickness of floor or partition. If plain sleeves are used, a plate should be placed around the pipe where it passes through the floor or partition. These are made in two parts so that they may be put in place after the pipe is hung. A plate of this kind is shown in Fig. 55. Valves. The different styles commonly used for radiator connections are shown in Fig.. 56, 57 and 58, and are known as "angle," "offset" and "corner" valves respectively. The first is used when the radiator is at the top of a riser or when the connections are like those shown in Fig.. 49, 50 and 51; the second is used when the connection between the riser and radiator is above the floor, and the third when the radiator has to be set close in the corner of a room and there is not space for the usual connection. A globe valve should never be used in a horizontal steam supply or dry return; the reason for this is plainly shown in
Fig. 59. In order for water to flow through the valve it must rise to a height shown by the dotted line, which would half fill the pipes, and cause serious trouble from water hammer. The gate valve shown in Fig. 60 does not have this undesirable feature, as the opening is on a level with the bottom of the pipe. Air Valves. Valves of various kinds are used for freeing the radiators from air when steam is turned on. Fig. 61 shows simplest form, which is operated by hand. Fig. 62 is a type of automatic valve; it consists of a shell, which is attached to the radiator. B is a small opening which may be closed by the spindle C which is provided with a conical end. D is a strip composed of a layer of iron or steel valve is as follows; when the radiator is cold and filled with air the valve stands as shown in the cut. When steam is turned on, the air is driven out through the opening B. As soon as this is expelled and steam strikes the strip D, the two prongs spring apart owing to the unequal expansion of the two metals due to the heat of the steam. This raises the spindle C and closes the opening so that no steam can escape. If air should collect in the valve and the metal strip become cool it would contract and the spindle would drop and allow the air to escape through B as before. E is an adjusting nut and F is a float attached to the spindle, and is supposed in case of a sudden rush of water with the air to rise and close the opening; this action is somewhat uncertain, especially if the pressure of water continues for some time.
There are other types of valves acting on the same principle. The valve shown in Fig. 63 is closed by the expansion of a piece of vulcanite instead of a metal strip, and has no water float.
The valve shown m Fig. 64 acts on a somewhat different principle. The float C is made of thin brass, closed at top and bottom, and is partially filled with wood alcohol. When steam strikes the float the alcohol is vaporized, and creates a pressure sufficient to bulge out the ends slightly which raises the spindle and closes the opening B. Fig. 65 shows a form of so-called "vacuum valve." It acts in a similar manner to those already described, but has in addition a ball check which prevents the air from being drawn into the radiator, should the steam go down and a vacuum be formed. If a partial vacuum exists in the boiler and radiators, the boiling point, and consequently the temperature of the steam are lowered, and less heat is given off by the radiators. This method of operating a heating plant is sometimes advocated for spring and fall when less heat is required, and steam under pressure would overheat the rooms.