Faulty Big Mouth?

dlipter

Bigmouth has replaced this vent.



During the steam cycle with the boiler operating between 0.5-1.5psi, the bigmouth hisses while emitting steam and appears to never close.

Is this normal? Any way to test it?

Thanks

KC_Jones

That's not a Big Mouth in the picture. If steam is coming out the vent is failed and needs replaced.

Fred

Not normal. Are you sure the pressure is where you say it is? How high is that Tee on the vertical pipe? I see it is reduced, just below the Tee. Any chance condensate is backing up in that vertical and keeping the big mouth too cool to close? Any issues with slow returns?

dlipter

The vent in the pic has been replaced with a bigmouth.

Fred

dlipter said:

The vent in the pic has been replaced with a bigmouth.

Right, but is the stand pipe configuration the same? If so, same questions I asked above.

dlipter

The return is just below the T which is 71" high on the return (vertical pipe).

dlipter

All pipes are the same.

dlipter

I could knock the drywall out above it and mount the bigmouth higher.

dlipter

That is the beginning of the return just below the T.

Fred

It should work. You may want to return that Big Mouth and request a replacement. They have had a few that leaked.

ethicalpaul

Is the big mouth getting hot enough that you can't hold it? It has to get pretty much steam-hot to close.

Crazy idea: Is your metal guard pulling enough heat out of the big mouth to prevent it from fully closing? I would have it standing in free air, not against anything.

ethicalpaul

Another idea (edit: this is @Fred 's idea!) There can be a lot of water flowing down that pipe, either condensate, or depending on your near-boiler-piping, you can have this kind of thing going on (go to 44 seconds in, this site doesn't respect the start point in the link):

https://youtu.be/WSRvvNQ5WLc?t=44

Either way, think of a waterfall of water flowing down the walls of that pipe. Any steam has to push through that waterfall to get up to the big mouth, probably taking some water with it. In my experience, the water starts flowing before the steam arrives at the main vent (and I have the sight glass to prove it--but my mains aren't insulated yet). So in the beginning of the cycle, it won't matter much, but once the steam gets to your return, I bet there is condensation water there.

Summary: For best performance, the steam should have a clear path to the main vent, from the top of the return instead of from the vertical pipe.

But I see what looks like asbestos up there so you might not have an easy solution here

Fred

@dlipter, I'm thinking there isn't enough steam left in that vertical pipe to actually hold the vent closed. Probably (maybe) just enough at first to struggle to close it but it cools down enough during the heating cycle to open back up. If you have anywhere actually directly off the main to relocate it, it will likely work much better. You can try to insulate the stand pipe the vent is mounted on and it may hold steam.

gfrbrookline

I agree with @fred the Big Mouth needs to be mounted before the drop.

I am guessing this isn't a parallel system and the pipe the vent is on goes to the basement floor or below so you don't have dry returns.

I would say you could cut another notch in the ceiling panel and add the vent before it turns down but those pipes look to be covered in asbestos.

dlipter

Yes the pipes are covered in asbestos. the internal disk appears to be firmly seated against the o-ring. When prodded cold with a wood stick the disk is floppy on its connection, when hot it appears to be solid, however I can see some mist comming from the exit hole. Maybe its normal and working.

Is there a way of mounting the Big Mouth on the main steam header without disassembling the pipes?

dlipter

On second thought the Big Mouth was spitting small amounts if steam which is why I added the sheetmetal deflector.

dlipter

Does it matter if the Big Mouth doesn't close completly.. so long as it vents well?

ethicalpaul

You’ll lose a lot of water vapor out of it, and some of your radiators may not get steam because it will go to the path of least resistance

Gsmith

The Big Mouth could be mounted directly on the steam main without taking the main pipes apart using one of two methods:
1) weld on a threadolet (a threaded fitting welded to the outside of the steam main (need to drill appropriate size hole in main first--with boiler off). see image:
2) drill appropriate size hole in main with boiler off and install a service saddle (available from several manufacturers, try Romac for one, but also search on this site for "service saddle" to see other manufacturers. Be sure to buy the EPDM special order gasket to make it compatible with low pressure steam temperatures. Here's a picture of an installed Big Mouth on a service saddle.

gfrbrookline

The big mouth will let out a little puff of steam for a few seconds before it closes, that is normal.

dlipter

What kind of drill bit should be used to drill into the main? Bimetal hole saw?

Gsmith

Regular high speed drill for steel. Start with. Small one, maybe 1/8 or 3/16 then enlarge. No real need to go much beyond the size of the Big Mouth male thread, not much steam flow needed to close the vent, just need a big enough hole to let the condensed steam go back to the main.