MainVents with Two-Pipe Condensate Pump?

gerry gill

the steam supply to a boiler return trap that the coal boiler used..could have been a vacuum breaker line from the return pipe at one time..your f&t traps are probably your main vents..if they are located at the ends of the mains they are.

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sreja

MainVents with Two-Pipe Condensate Pump?

We've just recently had a ton of work done on the two-pipe steam heating system in our 5 floor, 14 unit apartment building.

Reading and re-reading Dan's books I find myself still confused about the role of "Main Vents" in our system.

The first thing to say is that we do not appear to have main vents.

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What we have is maybe four F+T's here and there, and all the return lines feed into a condensate pump. The condensate pump has an air vent coming out of it, and in fact there is a pipe leading up and open to the air on the condensate return line before the line even gets to the condensate pump. You can feel air coming out of that when the boiler is starting up.

But there are no other main vents on the system.

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Now what we just recently noticed was something strange which has prompted my post..

Right as the main header is leaving the boiler room it takes an elbow and turns upward to start feeding steam to the system.

A small pipe T's out of that main header and starts to return into the boiler room. And it is CAPPED.

So i'm thinking this pipe might have once been a Main Vent? or connected directly to the return condensate line?

What confuses me greatly though is that if we simply connected that back to to the condensate return line -- it would be like a direct line from the steam header into the open air or condensate pump -- so that seems just plain wrong.

Would we put an F+T on that line and then lead it to condensate return pipe? since it seems from a small drip in that capped pipe that their is some slight water that gets into that pipe.

So you can see i'm confused about the role of an F+T vs. a main vent in this case.. Would an F+T piped to the condensate line (which is open to air) serve same role here is a Main Vent with the additional ability to handle some water condensation?

Or are they completely different things and what we should do it uncap and put a vertical Main Vent?

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I'm also just really confused by the operation of a main vent and the pictures in Dan's book (p115 in lost are of steam heating) showing the main vent attached to the Steam Main.

I mean it makes sense to me in a radiator where the steam rises and cold air would be let out the radiator vent.. but if you have a Main Vent attached right near the boiler on the steam main.. wont it either just close up right away when the hot steam hits it, or else let steam out?

can't wait to read the replies and learn more.. this forum has been such a great education.. thank you in advance.

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by the way some pictures of our system here though it's not so easy to see where the steam header leaves boiler room in upper right:
http://mouser.dcmembers.com/boiler/Picture%20008.jpg

Unknown

You didn't mention the location of the pipe teeing out of the main. I'm guessing if teed out of the top of the main it would be a vent line - on bottom (think gravity) for condensate.

The object as I see it is to have steam in the mains and not air. Vents let the air out but keep the steam in. The faster the steam is able to fill the mains, the faster it gets to the radiators which is where you want it.
On a one pipe system the vents on the radiator are pretty small so you need vents on the mains. You wouldn't want large vents on the radiators as they vent into the room and would spray out water droplets/dirt.

Venting in a closed two pipe system operates differently. My question for the "steam pros" is there any situation where a two pipe system would benefit having a vent on the steam side?

I imagine that in a lot of cases trying to figure out what the original system was and just how to modify it so works well, is a big job for the pros. I don't know if any of the mercury systems are still running in this day and age but I can just imagine how my PC neighbors would freak out if it was discovered that they had one. I'd love to be there to see their shocked faces!

sreja

Regarding the location of the small return pipe -- it's basically horizontal -- making basically a U turn back into the boiler room.

so i guess it's not so much a T as it is the giant steam main having an elbow going up into the building, and then a small pipe connected to the elbow which comes BACK into the boiler room and is then capped off. strange.

Fred Harwood_2

Capped line

Some older systems have a special mains el with a small (1 1/4) pipe leaving the el. It ensures that condensate making it to the main riser gets back to the boiler quick. It might be worth dripping that capped line back to the boiler, but well below the water line, perhaps in the condensate return line on the boiler side of the condensate pump. The pressure at the rising el and the boiler should be almost the same, and any condensate in the el can slide right back into the boiler.

sreja

The contractor who is finishing off work on the system has recommended we leave it capped.

Basically his explanation was something like this:

1.the steam main is rising up the height of the building.
2.this small 3/4" pipe which is leaving the bottom elbow of this steam main is about 6-10 feet from boiler header.
3. if condensate drips down that main steam riser (6" or so), it will flow back into the boiler header/equalizer pipe.

so that piping that small pipe back into condensate line from ceiling is not worth the trouble.

Fred Harwood_2

Capped line

Does the small line come off the lower side of the el? And does that el look like it was made just for that small line? If so, it is a condensate drip, whatever you chose do with it.

Mad Dog_2

The system NEEDS main vents...somewhere

and they were probably capped off at some point. Can you postr a few pics? Mad Dog

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Steamhead (in transit)

Because

"the steam main is rising up the height of the building" from this point, it should be dripped. Otherwise condensate will build up at this point, causing distribution problems and possibly banging. Remember, steam is moving from the boiler to this elbow and drip, which would tend to keep it from flowing back to the boiler. And, if water does flow back to the header it will quench the steam.

Install a 3/4" F&T trap on that drip and run the discharge back to the condensate tank.

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