Return lines in a two pipe system

Clank Clank

Assuming steam traps are installed, can radiator return lines be connected together before running into a wet return, or do they have to run to the wet return independently?



From other responses, a two pipe system with air vents (no traps) would not work effectively due to steam from one radiator finding its way to the other ...



thanks

Pumpguy

Being a pump guy....

I'm not an expert in these matters, but assuming the pipe diameter is large enough to handle the air and condensate flowing from the traps, and the pitch is downhill to allow a gravity flow of condensate down to the lowest wet return, I don't see why you couldn't pipe both returns together.

Hydronicz

hey

Id agree without the steam traps, the steam may flow up the return side to the higher floor radiator. If traps are installed I believe it will work fine.

Jamie Hall

If you have traps

and they are working... or if you have orifices correctly sized (and low pressure)... or if you have any one of a number of patented outlet widgets (and low pressure), then only air and condensate will pass out of the radiator through the return connection.  Traps or widgets physically prevent any excess steam from getting out; orifices limit the amount of steam getting in to what the radiator can condense.  Either way, no steam gets into the return lines.



The return lines, then, carry the air exhausted from the radiators (and, in some systems, from the mains) and the condensate from the radiators.  These lines are above the water line of the boiler, plus the A dimension, and thus are never filled with water -- just the condensate on the bottom.



Since they are carrying the exhaust air, they must be vented -- commonly where they join together near the boiler, but there are other schemes.



When the returns drop lower, below the water line of the boiler, they become wet returns (some systems really don't have them).  Since they have water in them, they will carry no air, only condensate.  The vertical lines down to the wet returns are referred to, usually, as drips.



The dry returns must be pitched to drain to a drip and thence to the wet return, but they can be either parallel or counterflow.



There were some very early two pipe systems which had air vents.  I think of them as one and a half pipe systems.  In these there were not traps or gadgets, and steam, for all practical purposes, flowed in both the returns and the supplies, but condensate flowed mostly in the returns.  They didn't work that much better than one pipe systems and, as soon as people figured out how to keep steam out of the returns but let the air and condensate out, they died out pretty quickly.  They do show up now and then.

Clank Clank

fooled ...

As you might have seen from my other post, i found the system with no traps but air vents. Never hearing of such a thing, i capped the returns, essentially giving me an inefficient one pipe system due to the small size of the risers and runouts (3/4") It looks like the system was originally intended to have traps so I might move in that direction.



3 out of the 9 radiators, as part of an extension off of a separate runout from the boiler, were not installed with 2 pipes but with one. If i put traps on the 1 subsystem and air vents on the other, seems to me these systems can co-exist. Is that true?



In regard to steam traps, where can they be found, researched, etc...



thanks