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2 Pipe - installing crossover trap @ end of main. Piping plan attached - feedback?

Hello Wall,

This is a 1920's Mouat 2 pipe vapor system where the steam mains and dry returns run parallel to each other for each of the two steam mains. There is currently no main venting on either main and 3 Gorton #2's on the long main's dry return and 2 on the short main's.

The boiler is oversized for the house (525,000 BTU/hr for probably 900 EDR, haven't calculated that yet) so I want to massively vent to keep runtime to a minimum. As many of you have figured out, Gorton #2s are expensive and somewhat unreliable when used as a steam main vent, so I was thinking of ways to minimize the cost of this venting project while maximizing performance. Attached is a piping diagram of what I came up with. Credit to all of the posts I read here on the wall for inspiration, and Gerry Gill's and Steve Pajek's Venting Capacity Chart.

The idea is to use Mepco 2E thermostatic 3/4'' radiator traps between the steam main drip and the dry return drip. These vent about 1.5x CFM as a Gorton #2 and I got them new on eBay for a third of the cost of a Gorton #2. I plan on using 3 of the traps in parallel, which nearly maxes out the max flow rate of a 1'' open pipe, and should vent my mains in just under one minute.

I intend to install an elbow facing up from the tee on the steam main drip to keep any condensate from hitting the traps, which should keep them cleaner and hopefully working for a long time. The traps would then outlet into a 1.25'' manifold which tees into the dry return.

Once steam hits these traps, they will close, and the venting antler on the dry return essentially swaps from being a main vent into venting the dry return. I intend to install a bunch of vents on this 1.25'' manifold, as I estimate that I have close to 40 cubic feet of air in the system aside from the mains. Thinking about 8 CFM at 1 oz for each of the two venting stations, using my existing Gorton #2s and some extra thermostatic traps I have. These should never see steam unless a radiator trap somewhere fails. The waterline of the new boiler is a good 3' below the old one, so not worried about water getting this high. Using a vaporstat with cut out at 4 oz.

Am I missing anything here? I assume these 90 year old pipes will be a bear to get off, and may have to end up cracking some fittings to get this work done.

Another side benefit of having one venting station instead of one on the steam main and one on the return is that if I want to play around with putting the system into a vacuum after a cycle ends, there are a lot fewer vacuum check valves to purchase.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 22,878
    Looks good to me, given what you are working with. You'll love it!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hvacfreak2
    hvacfreak2 Member Posts: 500
    That seems to be the way to do it on that system for sure. Just curious , how were those systems originally vented ?
    hvacfreak

    Mechanical Enthusiast

    Burnham MST 396 , 60 oz gauge , Tigerloop , Firomatic Check Valve , Mcdonnell Miller 67 lwco , Danfoss RA2k TRV's

    Easyio FG20 Controller

    OatKing
  • Dave in QCA
    Dave in QCA Member Posts: 1,784
    The Mouat system originally ran at about 3 oz of pressure at the boiler and it was controlled well. As a result, no other device was necessary to protect against rising water in the returns. Also, there were no vents on the mains or crossover traps. The condensate lines were vented with a special Mouat venting device which was designed to hold vacuum.

    Your drawing and plan looks good to me. The only thing I would do different is to vent the returns out of an open pipe, or elbow pointed downward. Think or a minute that if you were dumping your condensate into a vented condensate receiver, you would not put a steam vent on the vent outlet of the tank, in fact that is strictly warned against by the tank manufacturer. If all the traps are good, there is not problem. If one fails open, you'll start seeing stem wafting out of the tank. That is what you'd see if you simply vent your returns with an open port. You're protecting against rising water in the return via your vapor stat. It should work fine and you'll have super venting. Mepco 2E traps are super fast. Are you sure they're only 1.5? Someone told me a few days ago that they are 2.5 cfm, but I have not found it in print.
    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.
    http://grandviewdavenport.com
  • Frank_the_Tank
    Frank_the_Tank Member Posts: 20
    @Dave in QCA, funny you mention venting the return with just an open pipe, as that randomly came to me last night as I was thinking about the system. Looks like I might have a few 3 month old Gorton #2s for sale.
    The Mepco 2Es vent 1.53 CFM @ 1 oz vs the Gorton #2's 1.1 CFM.

    If anyone else is interested in the Mouat system, @gerry gill has their brochure uploaded to his site: http://www.gwgillplumbingandheating.com/webapp/GetFile?fid={63E7812D-C4E2-46BC-B4B9-18045A612CCD}

    Thanks to everyone for their responses. I'll post up the "after" pictures once the work is completed.
  • PMJ
    PMJ Member Posts: 1,265
    I agree with Dave and in fact have been running my Mouat system with only one single open pipe on the dry return (closed with a solenoid valve on off cycle) for many years. A two pipe system running at low single digit ounces of pressure needs surprisingly little venting even on cold startup. Getting any steam all the way through the small orifice in Mouat water seals on the rads to the dry return in the basement is almost impossible at that pressure. If vacuum is not needed just try the open pipe.
    1926 1000EDR Mouat 2 pipe vapor system,1957 Bryant Boiler 463,000 BTU input, Natural vacuum operation with single solenoid vent, Custom PLC control
  • Dave in QCA
    Dave in QCA Member Posts: 1,784
    @Frank_the_Tank Thanks for verifying the Mepco 2E is 1.5 cfm. I found the documentation in the Gill and Pajeck, Balancing Document. Let us know how your system works when you're done.
    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.
    http://grandviewdavenport.com