2 pipe steam fitting

2pipesteam

Home built in 1900. Two pipe steam with a natural gas boiler. No visible trap on the return side of any radiator. There is one main vent at the boiler on the return line. Each radiator has a Hoffman 1A 1/8” vent opposite the supply/return side of the radiator towards the lower third of the last radiator column. Radiators click and chirp and I’m trying to find the culprit. Radiator is properly leaning toward the return, pipes have space to expand and Contract. I found this fitting underneath the wood floor. Does anyone know what this is? It is on the dry return side of the line of each radiator underneath the floor.

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pecmsg

that’s a check valve

The direction of flow is right to left.

2pipesteam

Thank you!

mattmia2

the better question is why?

Jamie Hall

And the other question is — why are there air vents on the radiators? There shouldn't need to be, if the outlets go into a dry return.

The maximum cutout pressure for that system should probably be no more than 0.5 psig (8 ounces).

EBEBRATT-Ed

Someone probably added the rad air vents. Shouldn't need them but I guess they can do no harm.

Check valve are probably to prevent any steam in the returns from backing into another radiator but it the pressure is where it should be they shouldn't be needed.

2pipesteam

There is only one main vent Hoffman 75h for the whole system. Building is 4 floors with 4 radiators per floor. I think the vents on the radiators are to avoid having to put a vent at the top of the stack to balance the system and have it heat evenly. System is running at .5psig

Jamie Hall

Are there crossover traps from the mains or risers to the dry returns?

2pipesteam

No sir. The mains are counterflow and don't connect to the returns. I think this is a Donnelly check valve.

Steamhead

If this is a Donnelly system, those check valves would have tiny holes drilled in them so air could vent past them into the dry return. See the end of chapter 15 of @DanHolohan 's "The Lost Art of Steam Heating". If the main vent is on the dry return, that means air is supposed to be vented that way.

A Hoffman #75 or 75H is too small for this, however. You need at least one Gorton #2. Then remove the radiator vents and plug the holes using 1/8" plugs. If after doing this some radiators don't heat, disassemble the check valves and clear the vent holes.