What is this?

Bob Gagnon plumbing and heating

This is on a dry return for two pipe steam, No F&T trap on system, is this just a vent? It's a little hard to see, but there's another pipe coming off the top of the return, tying into the top of this device. The gauge is a vacuum gauge.
Thanks, Bob Gagnon

Paul S_3

vacuum breaker?

Steamhead

That's a "float trap/air eliminator" as described in Lost Art. It looks like an early Dunham. Essentially it's a main vent for the entire system, and has a vacuum check in the top. You will probably find crossover traps connecting the ends of the steam mains to the dry returns- these vent the air from the steam mains into the dry returns. All the air exits from this device.

Bob Gagnon plumbing and heating

Thanks for the quick reply Steamhead, the F&T device seemed to be piped different than Dan's diagram in his lost art book, does it look like it's piped properly? The ends of the steam mains, drip into a separate wet return, about a foot off the floor.
Thanks, Bob Gagnon

Steamhead

That's piped properly. It's not a float-and-thermostatic trap, just a glorified air vent. See page 230 of Lost Art for a diagram, and page 237 for how it fits into a system with a Return Trap.

Bob Gagnon plumbing and heating

Steamhead would you leave that vent in for a new boiler install, or would you use regular main vents? Why is the Vacuum gauge there?
Thanks, Bob Gagnon

nicholas bonham-carter

I would say that if the crossover traps are working properly, and that if the pressure is controlled by a vaporstat set for only a few ounces, then no conventional main vent is needed.
All the air will escape through that vent, and be prevented from reentering by the vacuum-check valve in the top. Steam will travel to the rads more quickly with less air in front of it.--NBC

Danny Scully

Actually, in this particular case, as long as a Vaporstat is installed you could remove the device all together and install proper main venting. If you felt so inclined to leave the device, you would still want to add proper main venting.

Jamie Hall

The thing about that contraption is that -- if it is working, of course -- that it does seal on a vacuum. That means that the system will continue producing some heat after the burner shuts off as it drops into vacuum. It also means that the system can get heat to the radiators somewhat more quickly when the burners fire up.

That is providing one critical thing. That the crossover traps, which were an integral part of the working of the system, are still there and are working properly.

If they are, and the contraption still works properly, you're home free. If they are, but the contraption is toast, put some good main vents -- as much overkill as you feel like! -- where it is. No need to go out elsewhere and add main vents. If, and only if, the crossover traps aren't working or have been removed, should you consider putting conventional main vents on at the ends of the steam mains. IMHO. And even then I would very seriously consider putting all the main venting where the contraption is, and repairing or replacing the crossovers.

Danny Scully

The Dunham home heating system wasn't a vacuum system. The picture I've attached is all that is inside that device. Condensate rise causes the float to rise and seal. The main downside to leaving it would be its 3/8 vent tapping. Greater venting could be achieved with either the existing 1/2" inlet or 3/4" outlet connections.

nicholas bonham-carter

I think the vacuum gauge shows that at one time there would have been a disk inside the top air exit fitting to act as a check valve, and maybe it is missing. Maybe it was removed when one or more crossover traps stuck open, or an oversized boiler was installed:
See page 62 of this for a picture of the vacuum check:

https://heatinghelp.com/assets/documents/dunham.pdf
--NBC

Sailah

I looked through all my old Dunham catalogs and can't find that air eliminator. I have lots of Sarco, Hoffman air eliminators here though. We even have a donkey cart full of NOS. I'll take one apart and post the pics.