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Vacuum Steam

I ran across a brief statement in an older UA Steam Manual; it cited that both supply and return lines in the vacuum system are smaller and therefore cannot be converted to any other system. I have been under the impression that only the return lines were smaller - please clarify.


  • other system

    what other system were you considering? when working properly, with all the various parts, vents etc working as they once did, are among the best systems you can have for steam. when the absence of pumps is factored in, their energy usage looks pretty good.--nbc
  • Dave in QCADave in QCA Member Posts: 1,660
    edited November 2011
    Usually smaller

    Perhaps the word should be "usually" smaller.

    For a true engineered vacuum system with a return vacuum pump, the piping was generally smaller.  Converting to steam without vacuum may cause problems.

    The reason that piping sizer were smaller was that the vacuum removed all of the air from the piping.  Pushing the air out of the system is a major factor in low pressure steam pipe sizing.   Also, when the returns are running in vacuum, there is a greater pressure differential between the supply and return piping and therefore flow is assisted.  
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • GlenGlen Member Posts: 855
    did a bit more research -

    and looked in the Dunham Manual circa 1925; specifically at the sizing tables - where the vacuum sizing tables for both the supply and return are considerably smaller than a 2 pipe & also have a much larger EDR capacity. "Always smaller" may not be true "always - but according to Dunham - they are usually smaller. thanks.
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