2 pipe problem.

upstateben

I'm not very well versed in 2 pipe steam and have ran into a problem on this call I received. Here's a little background. Commercial building 850000 btu boiler. (With hole above waterline looking at replacing after heating season) 2 steam mains each with their own return line that drop into a common dry return that runs around the perimeter of basement below the water line of the boiler to boiler feed tank that is vented to atmosphere.. There are f and t traps at the end of each main that are piped into low dry return. The problem the customer seems to be having recently is very little heat on the side of the building fed from one of the steam mains. The main is hot but the return line and most of the rads are cold. The other side fed from the other main seems to be heating fine. As I walked around the basement I found a check valve in common low dry return where the second steam main f and t trap and second return dump into the common lower return. My thought is the reason that one side isn't heating is because the air can't vent out due to the check valve. But I cant figure out why this would just start all of the sudden. Any thoughts?

Mike_Sheppard

Is it all dry return or is any of it wet? If they are wet returns there needs to be air vents. If dry returns only then it would vent out of the feedwater tank as you are describing.

Not sure about the check valve. Haven’t seen that. Do you have any pictures? Are you sure it is all dry return only?

Sorry, overlooked your picture. Those seem to be right near the ground. Are they full of water?

Are there air vents at the ends of the mains or top of the risers?

upstateben

They are below the water line of the boiler but are not full of water, they drain into the boiler feed tank.

upstateben

There are no air vents anywhere that I could see, other that the open pipe on the feed tank

ethicalpaul

I would think the hole in the boiler is probably the path of least resistance or little enough resistance that the balancing is fubar

upstateben

I guess I just am having trouble understanding how air could vent out of the one side of the system with the check valve installed on that return.

Jamie Hall

I would consider all those low returns to be wet -- or to have been wet at one time. Therefore, you must have or add venting to the true dry returns -- which will be up near the overhead level -- to allow air out of the radiators, and you must have or add venting on the steam mains, to let steam get to the radiators in the first place.

Do all the radiators have traps? Are all the traps functioning properly? Whack that mole first.

F&Ts seem to be very problematic as vents, and I wouldn't rely on them. If the radiators have traps, they will be double trapping anyway. If they are needed to get condensate from the ends of the steam mains into the dry returns, so be it -- although deep water traps are more reliable. If the lowered water level in the wet returns has allowed those water seals to be uncovered, that should be fixed too.

EBEBRATT-Ed

@upstateben
Sounds like a bad steam trap. IF the outlet from the steam traps goes to the boiler feed tank with no drop in the pipe (no water seal) then the vent on the boiler feed tank is your air vent and the f & T on that side is likely bad