Big Mouths: re-open on temperature drop or pressure drop (or both)?

Motorapido

Anybody know if the Barnes & Jones Big Mouth main vents re-open after a heating cycle based on temperature drop on the antler that the Big Mouth attaches to or due to pressure drop when the boiler shuts down? And for either answer, if it opens on temperature drop, at about what temperature does it open, and if on pressure drop, does it open when it returns to 0 psi or before that?

BobC

I opened mine up, it's a bellows that acts on temperature. It will open as the temperature of the vent drops.

Bob

Sailah

They are pressure agnostic. Temp only. 15-20 degree delta from sat steam temp and they start to open

EBEBRATT-Ed

It's a "thermostatic trap" so it only knows temperature

mikeg2015

That explains all my whistling on shutdown. Gorton 2 will,at least partially open under vacuum. Not an issue on most systems as they start at 0.5 psi and collapse from there. But if you run at 0.5 oz or less you drop into a deep vacuum faster that the boiler can add any more steam as vacuum forms.

EBEBRATT-Ed

@mikeg2015 , if you don't like the whistling install a check valve or a vacuum breaker

Motorapido

So if I time delay a few minutes between my vastly oversized boiler cycling in pressure, with my week insulated pipes, the temperature drop between cycles will likely not happen fast enough for my mains to refill with air, right? I don't want to waste fuel pushing more air out of the mains. I should note that I have 3 Big Mouths on each of my two mains, providing massive and excellent main venting, so I'm considering a brief break in rise time delay between cycles on pressure to allow more time for the radiators to continue to condense and put out heat before the next cycle starts.

Kahooli

If any radiator vent doesn't close, the system will fill with air after a collapse of steam. How long that takes depends on lots of things.

mikeg2015

EBEBRATT-Ed said:

@mikeg2015 , if you don't like the whistling install a check valve or a vacuum breaker

I tried. First one I tried cracking pressure was too high. Cut down the spring but now won’t always close when steaming.

May try another one. Found a few smaller ones with 0.3 psi cracking pressure. 1/4” probably be big enough.

Also tempted to put a check valve on every radiator but then the system would run at 4oz or more and probably be imbalanced as some would open at different pressures. What I need is a non spring gravity ball check or flapper.

Motorapido

@mike2015, we need to talk somebody into manufacturing this type of check valve specifically for this purpose. Granted, the market for these valves would be small, but it would really fill a niche.

gfrbrookline

If I read the Lost Art of Steam correctly you want your main vents to close and let the rad vents do the breathing after the first cycle. That is why you want to look at the drop away pressure of the rad vent so the system can breath. Page 107

mikeg2015

Motorapido said:

@mike2015, we need to talk somebody into manufacturing this type of check valve specifically for this purpose. Granted, the market for these valves would be small, but it would really fill a niche.

What I really need is to just convert it to vapor vacuum air line system (Paul system with without any vents). The big mouth of course will work great with it's threaded connection. I'm thinking I could actually zone my upstairs and downstairs using solenoid valves too. Big concern is the cost of copper or PTFE tubing and the vacuum pump.