Air valve releasing steam into wall

pacific214

I'm in a 2-family building with a one pipe steam heat system. A bedroom on the top floor has exposure on 3 sides (2 brick walls and roof) and there is no insulation so that room is generally freezing. I had Danfoss control valves installed on all the radiators in the building in order to try to balance everything (and will eventually renovate that room for a better building envelope). That room is open to 5, the adjacent room (roof and one exterior wall) is set to 4, top floor front is set to 3, and the entire 2nd floor is set to 2. Then we crank up the heat into the 70s so that bedroom is comfortable and no one else is too overheated. This solved most of the problem.
EXCEPT: The 2 bathrooms in the middle of the building, directly over the boiler room, have recessed Governale steel convectors and get way too hot. The air vent on the 2nd floor has been releasing so much steam that the top interior of the radiator cabinet is rusted and where there is a gap in the steel, the steam came through and caused water damage on the wall behind.
Now that I've explored all this and found these problems, I also see that the air vent is leaking water at the bottom and this has been running down and corroded the nut at the bottom of the unit. So immediate obviously fixes I see are that the bottom nut needs to be replaced (will this drain excess water from the system?) and the air valve needs to be replaced, but how do I solve this long-term? Can I plug the hole in the top corner of the enclosure? Is this air valve too close to the interior of the cabinet? Most important: is there an adjustable valve I can add to this as well so I can turn down how much heat enters the bathroom radiators?

Jamie Hall

Don't know about an adjustable that would fit, but... what is the pressure your system runs at? Often the problem with a damaged vent -- which is what you have -- is traceable to overpressure. While some vents can withstand up to 15 psi once in a while, most will die a quick and miserable death when hit with anything over 3 psi on a regular basis.

Therefore -- step one. Check your cutout pressure on the system and keep it below 2 psi. Make sure the pressure control really is working -- it's clean and the pigtail is clean.

pacific214

I did consider the system PSI and checked it. It's set to a little under 2 and the boiler was just went through it's annual thorough service so pigtail is clean.
The Danfoss on the regular radiators were installed in 2017, same time as these little convectors and their air vents so they've been taxed pretty hard for 6 years.

Jamie Hall

If that is an additive pressure control -- the simpler singe scale ones usuall aye -- that setting it the cutin. Set a little below 2 that usually means the cutout is around 3 or maybe even higher (there is an interior adjustment). Picture of the control?

pacific214

Oh interesting. You're right, is does say Cut In. I don't see anywhere else where there is a PSI adjustment but even so, wouldn't lowering the PSI affect the rest of the system negatively? What used to be in the bathrooms were small 6-fin cast iron rads. Maybe I made a mistake switching to these recessed convectors but at the time, my plumber did not advise me otherwise.
Sorry for the PDF - my HTML skills are zilch.

pacific214

This is what used to be there and no adjustments were made to the boiler when they were changed.

Jamie Hall

Actually lowering the psi will improve the whole system operation. Sounds strange, but it's true. Try setting that outer scale -- the one you can see -- down to a bit above 0.5, which is the bottom.

Then inside (take the cover off) there is a wheel which sets the differential between the cutin and cutout. It's probably set to about 1; if it is, leave it alone.

pacific214

OK I will check this out. But obviously I will also need to change the air vent. My understanding is that they are rated? Any suggestion on what type to get?