Door loop question

Double D · January 20

Is it necessary to go over the top of the door for a door loop on a 1 pipe steam system that's only returning condensate to the boiler?

Jamie Hall · January 20

Maybe. The first question to ask is whether this is a steam main extension or not, and if it is, where the main vent for that main is located. The consideration is that that loop under the door is a water seal, and neither air nor steam can pass though (unless the pressure is excessive, but that's another question).

The second question is what the piping is downstream of the door loop. You may get some interesting and unexpected pressure variations without the loop over the top, since that loop acts as an equalizer.

So… sort of depends on the situation, but in the absence of a pretty thorough knowledge and understanding of how steam, air, and condensate are going to flow, and what the pressure relationships are, that equalizing loop is a pretty harmless addition…

Double D · January 20

@Jamie Hall

Thanks for the reply.

I don't have any history on the building before I got there. All I know is the pipe going under the door has been there for many years.

At the present time when I operate the system it is obvious the return water on that side of the building is stacking and backing up into the end of the main every cycle. If running a pipe over the top will solve that problem, It would be the next thing I do.

Jamie Hall · January 20

worth a try. Something isn't venting properly, and an equalizing loop certainly won't hurt!

Double D · January 20

When you say something isn't venting properly do you mean the mains.

I tried using a big mouth vent on that main and the water came pouring out of it. I'm a little worried about using Gorton 2s, I would probably need 2 of them. I wouldn't want them to get damaged but at least they would close against water.

Thanks again

ethicalpaul · January 20

The under-door loop could be gunked up from decades of sediment

JUGHNE · January 20

Have you tried to clean the loop under the door?

That low spot would be a sludge trap over the years and if partially plugged would let water back up.

Some designs I have seen place a clean out on each end of the loop. This would require a pocket in the floor.

Just so that air can vent somewhere before that wet loop trap.

mattmia2 · January 20

It is no different than a wet return above the floor. If the vent is open it will pull in air to let the water equalize with wherever it joins to the boiler, if the vent is closed it will pull in steam from the boiler to equalize it.

EBEBRATT-Ed · January 20

You need the upper loop to carry the air. Lower loop caries water…….If this is a return. The tee for the outlet side of the loop is supposed to be 1" minimum below the entering tee. The 1" of water collum is to overcome the fitting pressure drop.

mattmia2 · January 20

https://forum.heatinghelp.com/discussion/comment/1883161#Comment_1883161

why would one pipe care about air beyond that it can get in at the vent?

Double D · January 20

The maintenance crew replaced the pipe onunder the floor.

This is only a wet return on a one pipe steam system.

Jamie Hall · January 20

If it is truly a wet return, then the loop shouldn't be needed. But… it shouldn't back up at all, since a wet return is open to either steam pressure or a dry return (not your case — one pipe systems don't have dry returns) on one end and the boiler on the other. Equal pressures.

If it's backing up, something is clogged somewhere…

EBEBRATT-Ed · January 20

@mattmia2

Door loops

It it is a steam main the steam goes through the top and condensate on the bottom so the upper pipe is larger.

If its a return larger on bottom carries condensate and upper is air smaller pipe. If with a return you will have a water trap on the bottom and without the upper pipe air can't get out. Need air vents on either side of loop

Door loop question

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