Document 44bB3Gq8vGpvQq9xzJGy064Oa

of and 1936American Society Heating Ventilating Engineers Guide, 31--Chapter Steam Heating Systems risers to the dry return main through-water seals about :36 in. deep, as shown in Fig. 9, to prevent steam from one riser entering another and closing the air valves on the nearest radiators. Down-Feed Gravity' Two-Pipe System The steam main in the down-feed system is carried to the top of the building, and the piping of the steam side is arranged practically as in the down-feed one-pipe gravity system. The drips at the bottoms of the steam drops and the runouts to the radiators are similar to those shown in Fig. 8 for the up-feed gravity two-pipe^system. On the return side of the system, the piping is arranged in exactly the same manner as the up-feed gravity two-pipe system. ONE-PIPE VAPOR SYSTEM A vapor system is one which operates under pressures at or near atmospheric and which returns the condensation to the boiler by gravity. The piping arrangement of a one-pipe vapor system is similar to that of the gravity one-pipe steam system; in fact, one-pipe gravity installations may readily be changed to one-pipe vapor systems by making a few simple alterations. The steam radiator valve is a plug cock which when opened gives a free and unobstructed passageway for water. The auto matic air valve is of special design to permit the ready release of air from the radiator and to prevent the return of the air after it is expelled. The air valves on the main are a quick relief type, and the whole system is designed to operate on a few ounces of pressure. 538 Cleanout Fig. 9. Method of Connecting Two-Pipe Gravity Returns to Dry Return Main y-Floer '7777777777777777777 TWO-PEPE VAPOR SYSTEM Two-pipe vapor systems may be classified as (1) closed systems con sisting of those which have a device to prevent the return of air after it is once expelled from the system, and which can operate at sub-atmospheric pressures for a period of four to eight hours depending upon the tightness of the system and rate of firing, and (2) open systems consisting of those which have the return line constantly open to the atmosphere without a check or other device to prevent the return of air, and which operate at a few ounces above atmospheric pressure. The open systems have the disadvantage of not holding heat when the rate of steam generation is diminishing. Under the first classification the essentials are packless graduated 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. 539