Cyclopedia of heating, plumbing and sanitation; a complete reference work . positions on different floors are con-nected with the same riser, which may run to the highest floor; and acorresponding return drop connecting with each radiator is carrieddown beside the riser to the basement. A system iii which the mainhorizontal returns are below the water-line of the boiler is said to 59 50 HEATING AND VENTILATION have a uh t ot sealed return. If the returns are overhead and above thewater-line, it i- called a dry return. Where the steam is exposed toextended surfaces of water, as in overhead retu
Cyclopedia of heating, plumbing and sanitation; a complete reference work . positions on different floors are con-nected with the same riser, which may run to the highest floor; and acorresponding return drop connecting with each radiator is carrieddown beside the riser to the basement. A system iii which the mainhorizontal returns are below the water-line of the boiler is said to 59 50 HEATING AND VENTILATION have a uh t ot sealed return. If the returns are overhead and above thewater-line, it i- called a dry return. Where the steam is exposed toextended surfaces of water, as in overhead returns, where the con-densation partially fills the pipes, there is likely to be cracking orwater-hammer, due to the sudden condensation of the steam as itcomes in contact with the cooler water. This is especially noticeable when -team i- first turned into cold pipes and radiator-, and the con-densation is excessive. When dry returns are used, the pipe- shouldbe large and have a good pitch toward the boiler. In the case of sealed returns, the only contacl between the -team. Fig. 23. Arrangement f Piping and Radiators in Two-Pipe System. and standing water is in the vertical returns, where the exposed sur-faces an- very small (being equal to the sectional area of the pipes),and trouble from water-hammer is practically done away with. Dryreturns should be given an incline of at least 1 inch in 10 feet, whilefor wet returns 1 inch in 20 or even 40 feet is ample. The ends of all-team mains and branches should be dripped into the returns. If thereturn is sealed, the drip maybe directly connected as shown in ; but if it is dry, the connection should be provided with a siphonloop as indicated in Fig. 25. The loop becomes filled with water,and prevents steam from flowing directly into the return. As the 60 HEATING AXD VENTILATION 51 Waler _ Lir-ie £j Fig. 24. Drip from Steam Main Connected Directlyto Sealed Return. condensation collects in the loop, it overflows into th
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