Document 1mrZVR9XwjQ5D2DkBrYpd79a

American Society of Heating and Ventilating Engineers Guide, 1937 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 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 31--Chapter Steam Heating Systems oipe size to provide for draining the riser, and if the drop is over three tories 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 and the normal size of drop required is 1 in. or less. The bottom of the steam 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 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. 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 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 552 f > Fig. 11- Typical Connections for Automatic Return Trap 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 return to the boiler or to waste, graduated or ordinary radiator valves, no automatic air valves on the radiators, thermostatic traps on the radiator returns, and the venting of all air from the system by means of pipes open to the atmosphere. The returns are open to the atmosphere at all timesr usually by extending the return risers to the top of the building where they are either connected together in groups and earned through the roof or extended through the roof individually. Atmospheric systems, either up-feed or down-feed, are often used where the condensation is not 'returned to the boiler, as in heating systems supplied by high pressure 553