Document 6RM1oQKDEzG53ypq6p3bkDQX9

Heating Ventilating Air Conditioning Guide 1938 Up-Feed Gravity Two-Pipe System This system (Fig. 8) has a steam and a return connection to each radiator.. The radiator valves for steam, return, and air are the same as those described for the gravity one-pipe air-vent system. The steam main is run and pitched in the same manner as in the one-pipe system, but the returns from each radiator are connected into a separate return line system which has its risers carried down and joined to a wet return line under the boiler water line level. Where the return has to be kept high to function as a dry return, it is advisable to connect the return risers to the dry return main through water seals about 36 in. deep,, as Chapter 15. Steam Heating Systems 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. TWO-PIPE 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 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 280 ^ Floor Fig. 9. Method of Connecting Two-Pipe Gravity Returns to Dry Return Main 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 valves on the radiators, thermostatic return traps on the returns, and traps on all drips unless they are water sealed. Such a system, illustrated in Fig. 10, should be equipped with an automatic return trap to prevent the water from backing out of the boiler. In this up-feed arrangement the supply piping is carried to a high point directly at the boiler and is graded down toward the end or ends of the supply main, each supply main being dripped at the end into the wet return or carried back to a point near the boiler where it drops down below the boiler water line and becomes a wet return. From this main, runouts are branched off to feed . risers or radiators above, these being graded back toward the steam main if they are not dripped at the bottom of the riser, or toward the riser if the riser heel is dripped. Both conditions are illustrated in Figs. 2 and 3. Return risers are connected to each radiator on its return end through 281