Two pipe system banging radiator

Levie

Hi I just replaced a steam boiler on a two pipe system the end of the mains on this system drip straight down to the wet return and do not have traps.
I'm having issues with a single radiator on the second floor banging on startup and I can hear the steam rushing through the radiator (as if it's pushing through water) and every once in awhile a bunch of gurgles as if the water is going down the radiator does get hot slowly but it's just making a lot of noise any ideas?
I did pitch the radiator it's a quarter inch pitch towards the return pipe.
Thx
Levi

Jamie Hall

If those radiator returns go straight down to a wet return, how are they vented?

Levie

Radiators go to dry return with a trap steam mains go to wet return 

Jamie Hall

Two possibilities come to mind. First, at the wet return location where the steam main drip comes down, is there also a dry return drip? And, if so, are both of them well below the present water line of the boiler? If not, steam could be getting into the dry return at that location and limiting the air venting from the radiator. The other which come to mind quickly is that one or both of those traps may be failed. If one of the radiators is working but the other is the problem, the one that is working may have a failed open trap. It the one which is guruling is your only problem child, that trap may be failed closed or partly closed.

Dave in QCA

Has the boiler been thoroughly skimmed, reskimmed, and skimmed some more?  New boiler is what sticks out to me.  If the boiler is priming and throwing excessive water up into the main, the lowest point, at the end, might be prone collecting water and pushing water into that radiator.  

I also wonder if your wet return lines were flushed out when the boiler work was done. That would also cause water to build up in the steam main. 

How is the air eliminated from your system?  Was anything changed with the new boiler? 

Can you provide some pics please. 

Levie

So the dry returns are not dripped at the end they are pitched back towards the boiler so the furthest drive return is the highest it's just a steaming right next to it that's dripped to the wet return.
In that area of the house the steam main does drip to a wet return which is quite high but it's a crawl space so that's the lowest it can go (I know excuses won't help me I have about five radiators over that crawl space and all the other ones work fine.
If it was the dry return getting steam I imagine it would get hot and I checked all the dry returns in that area and they are all cold.
Regarding skimming yes I just skimmed it for another 5 hours and added surge master I don't seem to be missing much water while it runs.

Can a trap be partially closed so not enough water drains and I get banging from that? The part that puzzles me is that it happens right in the beginning of the cycle before the radiator fills up.

I will try to get some more pictures when I'm back there.

Thx

Jamie Hall

If that "wet" return is above the water line, it's not wet. It is possible that steam or air, at the beginning of the cycle, is doing evil things to what water is in there. Check the whole length of it for any sags.

SgtMaj

If you have a two pipe system with radiator traps, and you have a new boiler, and you’ve never replaced the bellows in your radiator traps, odds are you’re getting steam in the return lines. I would replace the bellows in your radiator traps. Odds are many of them have failed, either open or closed. This maintenance item should be done about every 10 years or so. Do you know the last time the radiator trap bellows have been replaced?, or even your main line vents and return vents?

Levie

I'm going to go back and have a good look at that "wet return" which starts above the water line and slowly goes down I know there are two steam means that drain into it both above the water line or just about by the water line.
If one of the steam mains is causing the other to back up with water and shoot water into the radiator would that cause banging in the radiator or down in the basement by the steam mains? I'm having the banging inside the actual radiator and just wondering why on a 2 pipe system it wouldn't just drain out the other side?

Jamie Hall

Honestly, I'd have to look at it.

On @SgtMaj comment. I'd sort of agree -- but only sort of. On the plus side, those Sarco traps are easy enough to rebuild. On the minus side, however, a trap may last a lot longer than ten years -- if it's never been abused with overpressure. The ones on the system Cedric powers were installed in 1930, and are still fine...

SgtMaj

@Levie Is the radiator sloped toward the return end? If the radiator is level or sloped back to where the steam enters it will bang for sure. Put a level on it and make sure the radiator slopes toward the return. Steam travels light and fast, the condensate is heavy and can’t get out of the way of the steam *BANG!

Dave in QCA

Do I understand correctly that the returns are cold?  I suspect that the hammering is in the inlet pipe and that the sound travels to the radiator.   Water and steam in the same pipe will hammer amazingly.