vacuum vs non-vacuum valves in a 1 pipe low pressure steam heating system ?

Discussion in 'HVAC Heating & Cooling' started by DaveMe, Jan 16, 2012.

  1. DaveMe

    DaveMe New Member

    Messages:
    4
    Location:
    Denver
    I have a 1 pipe low pressure steam system and would like to replace the air valves on the radiators. The current valves are Hoffman No. 2 vacuum valves. When I look online, all I see is non-vacuum valves - like the Hoffman Model1A PartNo.401422 Air Valve (non-vacuum).

    I talked to a great steam system guy years ago (he is no longer around) and he told me to always replace the radiator valves with VACUUM valves.

    It seems like it is important to have the right valves in the radiators - but I am wondering if there is another thought about using non-vacuum valves today ?

    And if not, where do I find replacement Hoffman No.2 vacuum valves ?
  2. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,535
    Location:
    Houston, TX
    It may be best to contact the Manufacture and get their answer.

    I would want to use the Exact replacement it at all possible.

    If there is a acceptable replacement then they should be able to give you a part number.
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,301
    Location:
    Cave Creek, Arizona
    The system pressure determines how long it takes to produce steam, and the time it takes to evacuate the air in the system determines how fast the radiator will heat up. Using vacuum valves reduces the pressure in the system, and since they do not introduce air every time the heat shuts off and the steam condenses, they speed up both processes. Definitely use the vacuum valves.
  4. Runs with bison

    Runs with bison Member

    Messages:
    897
    Location:
    Midwest
    Nice explanation. I haven't ever had one of these domestic radiator/boiler systems so I have a question about this. In systems that instead introduce air as you describe, do you see a lot of corrosion? I'm accustomed to deaerators and such on industrial boilers, and any place where hot condensate came into contact with air the corrosion was rapid.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,301
    Location:
    Cave Creek, Arizona
    I have never seen air causing corrosion as a problem. But if you can keep air out of the system it makes it work better and faster. That is the reason for two pipe systems. They are sealed so air cannot get into them.
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