Document XRazB3ykORd3zw8ZpYoQaXevK

Heating Ventilating Air Conditioning Guide 1938 thermostatic traps. Their bottoms are connected to the return main through runouts which slope toward the main. The return main itself is sloped back toward the boiler if it is carried overhead; if run wet, the slope may be neglected, although it is desirable to slope the pipe so that the system may be drained. An air vent is installed at the point at which the return main drops below the water line. In the simplest cases this vent consists of a %-in. pipe with a check valve opening outward, but certain systems employ special patented forms of vent valves, designed to allow the air readily to pass out of the system and to prevent its return. A check valve is inserted in the return main at.a point near the boiler and a vertical pipe is run up into the bottom of the return trap, which usually is located with the bottom about 18 in. above the boiler water line. Some traps are constructed so that they will operate when they are installed Chapter 15. Steam Heating Systems the main (Fig. 7) and to drip the end of the main through the last riser, as illustrated in the down-feed one-pipe system detail shown in Fig. 6. If this is done, the pipe drop at the end or ends of "the mains should be enlarged one pipe size- to provide capacity for this concentration of the main drip. The steam drops are carried down through the building with suitable reductions as the various radiator connections are taken off until the lowest radiator runout is reached. If the drop is only two or three stories high, the portion feeding the bottom radiator should be increased one pipe; size to provide for draining the 'riser, and if the drop is over three stories high it is well to increase the portion feeding the two lowest radi ators one or two pipe sizes, especially if the two lowest radiators are small Air vent and check Fig. 10. Typical Up-Feed Vapor System with Automatic Return Trap3 "Proper piping connections are essential with special appliances for pressure equalizing and air elimination. with their bottom as close as 8 in. above the boiler water line. On the other side of this connection a second check valve is installed in the main return just before it enters the boiler (Fig. 11). Down-Feed Two-Pipe Vapor System In the down-feed two-pipe vapor system the steam is carried to the top of the building, the top of the vertical riser constituting the high point of the system, and the horizontal supply main is sloped down from this location' to the far ends of each branch. The branches are taken-off the main from the bottom or at a 45-deg angle downward, with the runouts sloped toward the drops (Fig. 6). Thus each branch from the main forms a drip and no accumulation of water is carried down any one drop. Another method of running the steam main, which is not considered as satisfactory but'which is practical, is to take the branches off the top of 282 Fig. 11. Typical' Connections for Automatic Return Trap - and the normal size of drop required is 1 in. or less. The bottom of the steiam drops should terminate with a dirt pocket above which a drip trap connection is located, as shown in Fig. 12. The returns on a down-feed vapor system are the same as on an up-feed system except that every steam drop must have a drip at the bottom connected either into the return through a trap or into a separate water-sealed drip line below the boiler water line, as illustrated in Fig. 10, in which case the thermostatic traps may be omitted. The runouts to the radiators and the radiator connections of the down-feed system are the same as those of the up-feed system already described. ATMOSPHERIC SYSTEM The. distinguishing features of the atmospheric system are gravity 283