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two pipe steam question

This past week we had a recessed fin tube convector with an air vent that went bad. The supply was a 1X 3/4X 1/2T.The 1'' was the inlet on the bottom. The 3/4" went up to the supply side, the 1/2" was a dripped wet return, pitched down to the supply with a check valve. This was connected to the air vent side. Apparently, the 3/4" supply would fill the convector with steam and the air vent would discharge the air. The check valve would keep the steam from goilg into the return and causing hammer or clashing. As the steam condensed, it would flow down the 1/2" wet return, past the steam and everyone was happy. I have never seen this before, after we replaced the air vent it works like a charm!

Comments

  • scott75
    scott75 Member Posts: 101
    two pipe steam question

    Is a steam trap required or can you just use an air vent? Can you use both? Is the trap on the return side?
  • It depends

    on the type of two-pipe system. The original version had vents on the radiators but not on the returns. Later versions did away with radiator vents and routed the air thru a trap, water seal or other device into a dry return which was vented.

    Ordinarily, you would not use radiator vents on a two-pipe system with a vented dry return.

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  • scott75
    scott75 Member Posts: 101


    I saw a system the other day that used finned tube radiation recessed in the wall with a cutout at the bottom and grill and air damper above. It was definately steam. I asked another guy from work it he had seen finned tube radiation with steam before and he said yes. I believe they had air vents. Don't know if they had traps or not as I didn't take the grilles off the wall to get a better look.
  • This type of radiation

    was most commonly used on Vapor systems, either with traps on the return connections or orifices on the supply connections. If recessed convectors were used with one-pipe systems they were usually cast-iron.

    I know of several 1930s houses in Baltimore that have recessed fin-tube convectors piped as two-pipe/air-vent! In this case the vents are on the return pipes in the basement, before they drop to the wet return.

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  • adayton_2
    adayton_2 Member Posts: 130
    Steamhead Burning the

    midnight oil I see.. :-)...The Trane two pipe system I have been working on has 14 regular OLD cast iron radiators and two recessed copper finned radiators in the living room. The steam TRAPS were installed as you say, below in the basement. They were installed however, about 3 to 4 feet downstream AND the piping has a serious dip in it causing hammering.(I presume return condensate is pooling at the low spot in the piping right before the trap) Steamhead, is it desirable to use a "throttled" orifice type feed valve on copper finned radiators? What technical function does this provide? Tnx Alfred/Jim
  • Only if you're not using traps

    or other devices to keep steam out of the dry return. Get rid of the dip and the hammering should stop, unless it has beaten the trap elements to death.

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