2 pipe steam fitting

2pipesteam · February 4

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.

IMG_4439.jpeg

pecmsg · February 4

that’s a check valve

The direction of flow is right to left.

2pipesteam · February 4

Thank you!

mattmia2 · February 4

the better question is why?

Jamie Hall · February 4

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 · February 4

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 · February 4

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 · February 4

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

2pipesteam · February 9

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

Steamhead · February 9

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.

2pipesteam · February 23

I’ve uncovered the ceiling in the basement. Attached are photos in pdf. They have the main going into a T fitting. As the main hits the T, one goes up as a riser and the other goes down and then back in the direction of the boiler where it goes back up and into the dry return to create of loop (see photos). The pipe is sized down after the T. There should be a trap in that loop back towards the boiler right? Even in a vapor system with a few ounces of pressure, sizing down the pipe isn’t going to stop steam from going into the dry return right? Why create the loop down, back, and then up off of the bottom of the main T? My thought was maybe they brought the water line to the ceiling and that loop brought them under the waterline? All of this piping is at or in the rafters except for the bottom of that loop, it’s at a lower point than all the other piping. Also, one of the branches off of the main is hot and then immediately cold. I’m assuming that junk in the pipe is stopping the flow of steam? Nothing seems to be sagging. The radiators fed by the blocked main still get hot as steam is flowing in through the return:-(. None of the fittings look like they have traps in the elbows.

Doc - Feb 22 2026 - 8-50 PM.pdf

Steamhead · February 23

The main drip should drop below the waterline and connect to the wet return. Even better, each segment of the main should have its own drip and main vent.

EBEBRATT-Ed · February 23

The drop in the pipe coming off the main makes a water seal to keep steam out of the returns. Looks like you have about an 8" rise their so you would have to keep your steam pressure lower than that to maintain the seal

mattmia2 · February 23

the steam in the return will stop the air from getting out of the runout from the main, the steam in the return is causing the steam to not follow that runout to the radiator.

Steamhead · February 23

@2pipesteam , where are you located? We might know someone who can help you straighten this out……….

2pipesteam · February 23

I am in Washington, DC.

Steamhead · February 23

Look no further:

https://heatinghelp.com/find-a-contractor/detail/foley-mechanical-inc/

Mad Dog_2 · February 23

Dan Foley will sqaure your issues away. Mad Dog

2 pipe steam fitting

Comments

Categories