What constitutes "leaking" on a big mouth vent?

wz25

Trying to isolate variables contributing to slow water loss. I have a 63-03L in North NJ. Piping was done by Dave a few years ago, mains are almost entirely insulated. I've had @EzzyT perform yearly maintenance (plus a water seal and low pressure gauge). Background in linked thread.

We lose about half a gallon of water a week, depending on how cold it is. There is zero water loss when the system isn't running, and I see no steam coming from the chimney. No buried wet returns. No obvious leaks at any rads. We had two big mouth vents - one for the primary main and one for the secondary; "had" because I just swapped one out. System cycles on thermostat - never seen the low pressure gauge budge.

I can confirm the BM vent on the primary "breathes" warm air while the main is heating. It's enough that I can collect a couple ounces of water over a few days, although my collection method is hardly rigorous, so I can't account for evaporative loss. I haven't checked the other BM since it's in a crawl space in the addition (inconvenient but entirely accessible). The BM is not billowing steam by any means, but I can't rule out failure to fully close on temperature.

I just replaced the primary main BM with a Gorton #2 and will monitor, but in the meantime, I'm curious (impatient) re: whether, assuming both BM vents behave in the same way, this could be a primary contributing factor to water loss.

https://forum.heatinghelp.com/discussion/178738/8-way-and-water-line-stability-after-numerous-skims

Long Beach Ed

My experience is that some vents are slower to close than others. I've never used the Big Mouth ones, but I find Gortons bi-metal type vents allow more steam to escape before closing than Hoffman sealed-expansion-vessel types.

I'm sure Big Mouths have their particular "rate of closure," so it is possible that this can cause a generous escape of steam over time.

Neild5

I have 8 Big Mouths at the end of the main, a Gorton #2 and 2 MoM #1 on 3 branches. The #2 is the slowest to close of the 3 styles. I do check the BM as they all did leak after 1-2 heating seasons, I replaced the original O-rings and have 5-6 seasons on all of them without any problems. The original o-ring was smashes and several looked melted, replaced with hi temp silicone rings from McMaster Carr.

Jamie Hall

Well… that's more leakage that I'd like to see, but looked at another way, it's quite possible that a vent closing — almost — against steam, or slowly against steam, could leak that much without in being a malfunction. if we scribble on a napkin for a minute, your loss works out to only half a pint of water per day — a cup of water.

JohnNY

neilc

turn off the fill valve John

delcrossv

https://forum.heatinghelp.com/discussion/comment/1830608#Comment_1830608

I have 3 Big Mouths on one main and they do occasionally leak steam (seen via mirror). I'm liking the silicone o ring idea. Do you have a McMaster part number?

Neild5

https://forum.heatinghelp.com/discussion/comment/1830682#Comment_1830682

1173N684 sealed the best.

109A_5

The Big Mouth with its threaded exhaust port could easily have some pipe added to collect some steam condensate and if pitched correctly it would return the condensate to the system. So less water loss.

delcrossv

https://forum.heatinghelp.com/discussion/comment/1830721#Comment_1830721

Ordered. Thanks!

ethicalpaul

The #2 is the slowest to close of the 3 styles.

This is not easy to determine when multiple types of vent are on the same main.

If the steam is traveling to the BM's first then sure they are going to close first. But I can't tell from your post if this is what you're timing here.

In my experience, a BM takes a LONG time to close, letting out a lot of steam. But that is a sample size of one.

Gorton #1 is fastest and Gorton #2 is also very fast closing compared to BM, again, just according to what I've seen.