Steam moving backward, from the dry return to the main

steve_81

Just had new one-pipe gas steam boiler installed - Weil Mclain EG 45 PIDN. 3" riser out of the boiler to 3" header (24" above water-line) down to 1 1'/2 equalizer and hartford loop. Two, two-inch risers off the header. First riser to main run A, as steam travels, has a reducer from 3" to 2".. Second riser to a second main B does not have a reducer. Steam is moving well through main A, but not through main B. After 10 minutes, main A and dry return is hot. In 15 mins, main B still cold, but the dry return starts to heat as steam moves in reverse through the return. Eventually steam makes it all the way back to the boiler through the main after about 30-40 mins.



All pipe in black steel. Total length of both Mains and returns are within 5 feet of difference. All vents working, even trying main vent at end of main B. No hammer, surprisingly, during all this. Should be parallel flow system, but would say i'm working counter flow in half my system at this point.



After second riser, we only have about 2" of the 3" header pipe until the ell at the equalizer? I've heard there should be at minimum of 6-8" here on a residential system. Pitch is not great on main B and returns but cant' find any level spots or incorrect pitch. Main/return B does have have twice the number of elbows as compared to Main A



Were going through engineering books. Running less than 1lb pressure. Searching for answers. help....

Hap_Hazzard

Do the dry returns connect above the water line?

If they do, then there's your trouble. Steam will follow the path of least resistance. Unless the main venting is balanced very closely, and the connected loads are similar, one branch will always starve the other. It doesn't even matter which one comes off first. You won't always see the steam backing up through the return like this, but you will always pay the devil trying to balance the venting.



If that tee in the upper left of the picture is where the two returns are joined, your job is easy. Just extend the drip on the right to somewhere below the Hartford.

crash2009

As Hap was saying

 easy fix Steve.  Just drop the return down below the water line.

Hap_Hazzard

Guess how I know this.

Yeah, I screwed up. I managed to balance my mains in spite of it, but it wasn't easy. In my case it's a lot harder to fix. I need to run another return.

Kevin_in_Denver_2

How is the steam getting through the Hartford Loop?

Unless the Hartford loop joins the equalizer above the boiler water line, I don't see how reverse steam flow can occur. If it were too high, (which it doesn't appear to be), then the condensate line could be dry in a new system, and steam could get through.

Hap_Hazzard

I doesn't have to.

If the mains are connected via their dry returns, above the water line, the steam never has to go through water to move from one main to the other. It just goes wherever it encounters the least resistance to moving the air out of its way.

crash2009

The Hartford loop

 doesn't even come into play in this situation Kevin.  The steam is coming out of the boiler, going to the end of the main, (short circuiting) and then travelling the wrong direction up the second main, and back to the boiler.  Dropping the end of main into the wet return will prevent this from happening.

steve_81

Thanks. Makes sense

Any opinions on my plan to lengthen the header by 6-8" beyond the second tee/riser of Main B? Will it promote even heating of both mains? I want to make sure the second riser is not starved or seeing back-pressure from the close turn equalizer ell.

Connecting the Main B dry-return below the boiler water line will resolve backward steam, agreed. But while it's torn apart, I would consider doing this if overall efficiency of the system is improved.

Thanks again.

crash2009

Are you sure

 that's an EG-45?  and/or Are you sure the boiler riser is 3" ?  The reason I am asking is that the manual says the boiler tapping is 2.5"



http://www.weil-mclain.com/en/assets/pdf/eg_boiler_manual.pdf



How many burner tubes does it have?  The EG-45 has 6 tubes, The EG-55 has 8 tubes.  What does the ID stamp say it is?

ChrisJ

tappings

Crash, all of the WM EG series boilers have 3 inch tappings I think, so he is correct on that. I bushed mine down to 2" on both, but used both tappings as I felt it was a better trade off on cost. I thought you had an EG-55 with 3 inch risers, no?



I agree with everyone in that he needs to connect the returns below water otherwise the problem will continue.



I'm also curious what venting is used on the mains as I didn't notice it mentioned? I'm falling asleep so there is a good chance I missed it.

crash2009

I do have a 55

 it does have 3" tappings, I used both tappings and we came out of the boiler full size (3"). 



I was just questioning why Steve says his EG-45 is 3" and the manual says 2.5". 

ChrisJ

Ah

I don't recall the manual saying it had 2.5" tappings.  If I remember correctly it only shows minimum size piping for different sized boilers.  I think the returns are 2.5" tappings. 



Remember, the EG-45 and EG-55 most likely have identical end sections (front and back).  Its only the quantity of middle sections that change.



One thing that confuses me about the EG series manual to this day is why the EG 40, 45 and 50 have two different columns showing different sized piping.  They are the only ones like that in the chart.