Why does the steam not go out of the air vents?

BUSTERBATBOY

I read this in a trade magazine:
"For a steam system to operate correctly, the air has to be removed from the pipes and replaced with steam. Since the two gases — steam and air — cannot occupy the same space, steam at a higher pressure will push the air from the pipes through the air vents or traps."

JUGHNE

The vents and traps have a high temp thermostatic valve that closes upon the arrival of the steam.

Keep reading, a good book is "We Got Steam Heat!", easy and interesting read .

BUSTERBATBOY

Aha! Thank you kindly.

dean_20

An even better one is "The Lost Art of Steam Heating". And I'm just a homeowner who just happens to have a one pipe steam system.

JohnNY

But, as with all things mechanical, those thermostatic valves do fail at times. They're one of the very few moving parts in a simple steam heating system and they need attention once in a great while. Just saying.

ChrisJ

JohnNY said:

But, as with all things mechanical, those thermostatic valves do fail at times. They're one of the very few moving parts in a simple steam heating system and they need attention once in a great while. Just saying.

How long do they generally last, assuming the velocity through them is low as to not carry rust, debris etc and assuming dry clean steam?

Jamie Hall

ChrisJ said:

JohnNY said:

But, as with all things mechanical, those thermostatic valves do fail at times. They're one of the very few moving parts in a simple steam heating system and they need attention once in a great while. Just saying.

How long do they generally last, assuming the velocity through them is low as to not carry rust, debris etc and assuming dry clean steam?

If they have never been abused -- particularly overpressure, or steam in the returns -- a long time. The ones in Cedric's home were installed in 1930, and are fine.

Even a relatively short overpressure, though, can ruin them pretty fast.

mikeg2015

Also, if the steam fills the radiator too fast and/or is wet, it will mix and you get a lot of warm vapor that is too cool to close hte trap but will spit out the vent. Solution is properly near boiler piping and slowing the radiator vents and speeding up the main venting.

Gordo

@BUSTERBATBOY : Here is a YouTube video showing and trying to explain what goes on inside a typical steam radiator vent.
Sorry about the low volume sound (Earphones might help).

https://www.youtube.com/watch?v=U1HZUxhEFO4

mikeg2015

I see you have a Hoffman 1A vent there. You happen to have a stash of those? It’s a really slow vent and I’m considering converting back to vacuum. They apparently last forever too. The one I have I think is original from about 1907.

BUSTERBATBOY

Thank you all.