Odd Set Up Two Valves on a one pipe system

Grallert

Hi folks
One of the properties here at MHS I care for has quite an elaborate steam system. It's a one pipe system that's zoned with mechanical valves. Maybe a dozen zones. I've been slowly plinking away at it when I can get a break for the school.
Trying to solve spitting and banging. My question is about a radiator on the second floor in one of the Main baths. This does ring a bell but I forget why. Would someone be so kind as to educate me on the reason for two valves on a single pipe system?

JUGHNE

That rad may be a 2-pipe with air vent. Does the return go down and connect into a wet return? It is in TLASH.

Grallert

I knew I saw it somewhere. It's odd though isn"t? And it's the only one. I wish I was here while they Dead men were doing it. Well really not but I'd love to find a note somewhere.

JUGHNE

It is in the bath room, You say? Maybe not connected thru a zone valve. With the 2 pipe you could throttle the inlet as the condensate would drain out the return side.
This would maybe always give heat to the bathroom when the rest of the area was not getting heat because zone valve closed. WAG on my part.

Grallert

That's some thing I didn't consider. I'm going back there tomorrow and I'll see if I can find where it emerges in the cellar. I wonder why a trap wouldn't have been used.

JUGHNE

If the return connected to a wet return lower than the water line, (with enough water seal/height) that would be the seal. Or perhaps a wet loop trap to keep the steam out of a dry return. Traps may not have been invented or well accepted yet..... plus the cost.

That rad should slope down towards the return/ air vent end BTY I believe.

Grallert

Thanks for that. I think I have it wrong. Never stop learning

JUGHNE

Yes, I noticed your lever there. You need to be opposite of 1P rad condensate drainage.

Ironman

Here's an article about 2 pipe air vent systems:

https://heatinghelp.com/systems-help-center/two-pipe-air-vent-steam-heating/

Grallert

Thanks for this. As Mr. Holohan has said. I pays to wander away from the wall sometimes.