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Minimum distance to take-off to Mains?

vaporvac Member Posts: 1,520
In the new install of the 2 tr50 (starting this Thursday) we are very close to the original take-off to the mains. We would really like to avoid having to take part of it apart. The constraining factor is the distance from the last dropped riser into the header. We need about 16". Is this written in stone? We're fine on the equalizer side, but so close with the take-off. It's a very tight fit with barely the minimums met for distances. It would just be really nice not to have to remove 300 lbs worth of metal.
Two-pipe Trane vaporvacuum system; 1466 edr
Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF


  • Drop header dimensions

    Where does that 18" requirement come from in the distance from supply to riser?--NBC
  • BobC
    BobC Member Posts: 5,182
    It would be nice, but

    I recall a thread where Jstar said it just isn't possible in a lot of installs to use the recommended riser spacing. If you look at the pictures of installs done by the pro's on this site I think you'll see it just isn't possible in many situations without tearing apart a lot of existing piping.

    I wonder what the difference in performance would be between the recommended and the possible.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Bio
    Bio Member Posts: 278
    edited November 2013

  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,288
    I think it goes to show

    What you can get away with when you don't cut any corners. These guys see the IOM specs as minimal requirements rather than something to strive for, so they build extra capacity into everything they can, and that gives them a margin for compromise when dealing with architectural constraints. So where in some cases it might cause some water to get trapped in the header if the system riser is too close to the boiler riser, it can't if you've already wrung out every last drop and your velocity through the header is very low. Whereas if you cut corners and do knucklehead work, something like this would be like the last nail in the coffin.
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • MDNLansing
    MDNLansing Member Posts: 297

    It doesn't look like the manual states a minimum distance. How much will it be in your install and where did you see the 16" minimum restraint?
  • vaporvac
    vaporvac Member Posts: 1,520
    edited November 2013
    Depends on manufactuer, but for Slantfin....

    Thank you Bob. I couldn't for the life of me remember who had written that post, but I remembered it. And as HHazzard states the PROFESSIONALS can get by with these things because they've gone so far beyond the minimum in the first. This is NOT the case here, although I've tried to do the best I can.  Fortunately, SFs minimums set the bar high.

    NB-C and MDM,  some manufacturers just say 15" . Slantfin tr50s are based on the diameter of the dropped header. Can't remember what's recommended for a single boiler, but for my twins, it's 4 diameters from last riser to take-off to mains and 3 diameters from take-off to equalizer. My drop header is 4" so that makes 16" and 12" on the equalizer and that's what I planned for originally.

    SF's I&O manual is dense and then there's a different one for gas not on their site and also for modular stage-fired settings so it's easy to miss.

     It now looks like we need to take the mains down from the horizontal flange so we'll just take down the whole thing in one piece. We'll see if we need to alter anything after the boilers are set. My little scale drawing is slightly off so I'm hoping it has a bit of play to allow reusing the mains piping basically "as- is".
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF
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