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

Frank_the_Tank

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.

Jamie Hall

Looks good to me, given what you are working with. You'll love it!

hvacfreak2

That seems to be the way to do it on that system for sure. Just curious , how were those systems originally vented ?

Dave in QCA

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.

Frank_the_Tank

@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

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.

Dave in QCA

@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.