Sometimes a separate drip is carried down from each set of radiators, as shown on the lower story, being connected with the main return below the water-line of the boiler. In case this is done, it is well to provide a check-valve in each drip below the water-line.
In buildings of any considerable size, it is well to divide the piping system into sections by means of valves placed in the corresponding supply and return branches. These are for use in case of a break in any part of the system, so that it will be necessary to shut off only a small part of the heating system during repairs. In tall buildings, it is customary to place valves at the top and bottom of each riser, for the same purpose.
Radiator Connections. Figs. 30, 31, and 32 show the common methods of making connections between supply pipes and radiators. Fig. 30 shows a two-pipe connection with a riser; the return is carried down to the main below. Fig. 31 shows a single-pipe connection with a basement main; and Fig. 32, a single connection with a riser.
Care must always be taken to make the horizontal part of the piping between the radiator and riser as short as possible, and to give it a good pitch toward the riser. There are various ways of making these connections, especially suited to different conditions; but the examples given serve to show the general principle to be followed.
Figs. 20, 21, and 22 show the common methods of making steam and return connections with circulation coils. The position of the air-valve is shown in each case.
Expansion of Pipes. 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 off sets 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. 33. 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. 34. 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 parti tions, the wood work should be protected by gal vanized-iron sleeves having a diameter from to 1 inch greater than the pipe. Fig. 35 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. 36.
Valves. The different styles commonly used for radiator con nections are shown in Figs. 37, 38, and 39, 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 Figs. 30, 31, and 32; 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. 40. 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. 41 does not have this undesirable fea ture, as the opening is on a level with the Air-Valves. Valves of various kinds are used for freeing the radiators from air when steam is turned on. Fig. 42 shows the simplest form, which is operated by hand. Fig. 43 is a type of auto matic valve, consisting of a shell, which is attached to the radiator. B ;s 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 and one of brass soldered or brazed together. The action of the valve is as follows : when the radiator is cold and filled with air the valve stands as shown in the cut. When steam is turnel 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 ex pansion 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. 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, however, is some what uncertain, especially if the pressure of water continues for some time.