Mains joined at ends

Enreynolds

I have a system where the two Mains are joined together and drop into a dry return at their ends. I know this is causing distribution problems, because the steam is taking the path of least resistance, bypassing risers to the third floor. I am thinking of dropping a water loop down below the water line in the dry return between the ends of the Mains. Will this isolate the Mains from each oth?

Dave in QCA

Yes, it will work.

I had the same problem.  One of the large loops had a shorter loop of the side.  The ends of the mains combined to one main, then proceded to the vent, and then dropped to below the water line.



Was fairly simple to separate the mains, vent them both, then drop to below the water line before tying them together.  Yes, it will work.

nicholas bonham-carter

Bypassing the riser

Certainly, the dry returns should never join above the waterline, but I think that is more for water-hammer prevention.

I don't see why that would short-circuit the riser. Have you tries the vent off the radiator test as the boiler is continuously firing (with a helper ready to cut the boiler before all the wall paper is removed)?--nbc

Enreynolds

Strange outcome

Thanks, Dave. Installed a Waterloop with strange results, to follow.

NBC, we did try the open vent trick,and did get panting from the radiator, but no steam until all other radiatora fully heated across. I think that some of the radiators on the shortcut side are filling/condensing/sucking in more steam, hogging the steam.



Installed the loop, added a G2 to each side, and fired the boiler. Starts steaming, G2s vent loudly, and former cold radiators start heating along with rest of radiators. Add two more G2s, to allow more venting at lower pressure, and radiators no longer heating.



Any insights?

Dave in QCA

more questions

This is one-pipe, right? 

What kind of vents on the radiators?  All of them the same?

Are you saying that when 2 additional G2s are added, that your previously cold radiators stop heating?

Dave in QCA

Joined above the water line

nicholas, I think what usually happens when two steam mains combine above the water line is usually one main will be filled with steam first, causing the vent to close and leaving the other main still filled with air with now where to vent besides throught he radiators.  I had a situation where a short loop went of the side and then tied back in to the "end of main" or dry return of the steam main as it came back to the boiler.  The short loop would fill with steam and close the vent very fast while the much large and longer main would not be well vented at all.  Even in a system where there are 2 vents, and the returns drop but connect above the water line, if one loop vents fast than the other, as soon as its vent closes the steam will travel backward up the return of the second loop, heading to that vent that is still open.  As soon as it gets there, of course it will close, even though there may be a bunch of air left in that main.

I don't think my explanation is very good... but I'm doing my best.

Enreynolds

Converted Paul system

Dave, unfortunately, this was originally a Paul system that has had the vacuum pump and most of the return lines removed. The vents are a mish mash of old vents, new Hoffman 1as and vari-vents. I think this is part of the problem as well. Yes, after adding more main venting, the cold, then warm radiators were again cold.

Dave in QCA

2 Recommendations

As has been said so many times, and is the key to even distribution in a one-pipe system, "Vent your mains fast and your radiators slow, but completely."



You've got the main venting taken care of now.  So, the problems are with radiator venting that is too excessive. 



There are 2 ways you can solve it.  1. Buy a whole batch of new slow vents.  Nicholas swears by the Hoffman #40 and I have to say it is my favorite too.  Or, 2. you could adjust all of your vents to a real slow spead.  If this is in an apartment building, you will have a hard time keeping them from being readjusted.  If you varivents are Dole, you want them set at 1.  The Hoffman 1A can be set just a hair above 2., but you will have to take the screw off and look inside it as you are positioning it because the way it is designed there is so much slop on the way it mounts that merely dialing the adjuster to "2" could giver your possible results all over the board.



BTW, if you happen to have HeatTimer Varivalves, even in their slowest position the will be way to fast to work for you.