Another CO2 leak

[starkers]

I've run into some strange gas leaks on my new kegging system. I resorted to starting from just the reg and reconnecting one thing at a time, static pressure testing as I go by pressurising the system then closing the gas bottle's tap. Looks like I have 2 "bad" QDs, one good QD and 2 "good" kegs (also a third bad keg, but that's a challenge for another day).

The good kegs hold 15psi indefinitely when I attach either the good QD or a spunding valve via their gas posts. That's why I say they are good, including their gas post o rings.

The "bad" QDs hold pressure fine when they're not connected to a keg, but once I attach them to the good kegs, they have a very slow leak.

I thought about the top of the QD housing, but that's under pressure regardless of whether they're connected to kegs right?

My only remaining theory is that the post o rings are just thick enough to be ok with some QDs, but a little bit of manufacturing variance in the surface where the O rings mate the QDs means it fails on some QDs?

I've done the soapy water and I can't find issues. Does anyone have any wisdom? The QDs are kegland duotight ones if relevant, and the kegs were brand new so should have good rings. Everything is greased

 

[golfandbrew]

If you have isolated to the posts on the kegs I would recommend going ahead and replacing the post orings as your next test.

You have you tried all QDs on all the posts, correct? I suppose you may find that one of the QDs is bad this way also and would not test them on the new orings until you have confirmed the leak is fixed with a new oring. Hopefully that makes sense.

Curious to hear about the "bad" keg and where that leak is?

 

[starkers]

Thanks, yeah I've tried all 5 gas QDs that I have on hand on each keg, with three sealing on both kegs and two leaking on both kegs. The leaking QDs seal when they're not attached to a keg though, so that's why I was wondering about the O rings being marginal and manufacturing tolerances in the QDs making the difference. I'll head to the lhbs on Wednesday for some new O rings to try.

Not sure about the bad keg yet but it definitely seems like a different problem, it leaks fast and irrespective of whether there's a disconnect attached, so candidates are probably the post (but where it joins the keg, not the outer O ring), the PRV, or even the lid gasket

 

[golfandbrew]

And you have sprayed soap all over the QDs, posts, and duotights? If it's s a small leak either mist of soapy water or spounging with really sudsy water might help isolate the leaks.

 

[mynameisrodney]

I've had a leaky QD that had a scratch on the inside of it before. Pretty sure that was letting gas past the O-ring. No idea if it was like that when I bought it or if I did it putting on a post. I just binned it.

For the kegs, I have read many people say to first pressurise a keg to 30psi to seat the lid O-ring properly, and then turn it down to serving pressure to prevent the lid o-ring leaking. I have never personally needed to do this, so no idea if it is true or a myth. It might come from back in the day that people were mostly using 2nd hand kegs that were much more worn out. In any case it might we worth giving this a try.

Also for the keg, dont forget to spray the prv.

Lastly, next time you do a soapy water test, check your soap solution first and spray everything before connecting it together.

 

[Mitchoor]

The other thing you might need to check is your gas lines to the the keg, i had one that was leaking it was not until i replaced the line all together that i found my leak.

 

[hotwaterpls]

I'm not sure about the new duotight disconnects, but the standard disconnects (barb or MFL) have I think three o-rings including two in the housing (one being for the poppet) and one in the underside where it goes over the keg post. It could be that one underneath is worn so when the poppet on the keg is pushed down, gas is allowed to escape past that o-ring, while the one inside the disconnect is fine (hence holding pressure when not connected).

I have a gas disconnect that works fine when on a keg, but leaks slightly when pressurised (it's on my transfer lines and can hear it hiss when disconnected). I also have a poppet on the liquid side of one keg that doesn't always seat properly and one of my keg lids is old and needs a burst of co2 to pressurise (otherwise it will leak slowly). I've also had a prv with a slow leak, but a bit of keg lube seemed to fix it right up.

If you think it's where the post connects, it may be the gas post o-ring. It can be tricky to spot those so make sure your soap solution is bubbly or if you can, submerge the whole keg or whole section to spot the bubbles.

Best of luck!

 

[Liambeer]

I had dramas with disconnects with a new system and lost two bottles of gas. I replaced all disconnects with genuine John guest(all others are a copy of these) they are expensive but cheaper than repeat empty gas bottles

No issue since

 

[mynameisrodney]

I have a bit of a dogs breakfast of different brands on mine due to upsizing a bit at a time. the only ones I repeatedly had issues with are the unbranded stainless steel ones so I ditched them.

 

[Ballaratguy]

I’ve found that duotights will leak if there is pressure placed on them. The tube needs to be straight out of the duotight with absolutely no sideways pressure on the or they are likely to leak
I use hose barb connections on all we now

 

[mynameisrodney]

I’ve found that duotights will leak if there is pressure placed on them. The tube needs to be straight out of the duotight with absolutely no sideways pressure on the or they are likely to leak
I use hose barb connections on all we now

Are you sure you are in past both O-rings? That's how they behave for me if they're not all the way in. I also don't think they work as well with other brands of tubing as they do with the EVABarrier. JG fittings work well with any brand of tubing I have tried.

 

[Ballaratguy]

It was Eva tube cut square and inserted all the way
Not a problem with hose barbs and clamps

 

[starkers]

Thank you all for your suggestions. Touch wood it seems to be holding pressure now. I replaced the post o rings, it still leaked, I pulled the QD off, put some soap on it and the post, turned the keg upside down so the soapy water would settle in the little grooves and reconnected - no leak. Turned the keg back up the right way, disconnected and rinsed off the soapy water, still no leak. I still have no idea what was leaking, but for now it’s stopped. I’m not filled with confidence, because it feels like maybe a little crack got gummed up with soap or something, but for now I will take what I can get.

Also, I realised something really odd earlier today before I had this accidental breakthrough - I noticed that only the high pressure gauge was going down slowly when I turned off the tap (ie the gas trapped between the bottle’s tap and the reg was draining), but the low side was staying at whatever pressure I set it to. I have absolutely no idea how an issue with the post or disconnect could cause that. If you’re thinking that sounds like a gauge or washer leak, I would agree, except that I could literally watch the needle falling with the QD connected, then pull it off, and the needle would stop falling

 

[starkers]

I’ve found that duotights will leak if there is pressure placed on them. The tube needs to be straight out of the duotight with absolutely no sideways pressure on the or they are likely to leak
I use hose barb connections on all we now

I see your point and I did have some trouble getting the FFT-duotight adapters on my manifold and reg to stop leaking (lots of talk about people over tightening these, but mine were actually the opposite). As I expand or replace stuff I will move away from them on the gas side, and maybe keep them on the beer lines.

However, I am confident that it’s the disconnect itself this time and not the seal between the hose and the duotight, because it only leaks when the disconnects are connected to the keg

 

[FarsideOfCrazy]

Put the disconnect in jug of water and gently wiggle the line

 

[mynameisrodney]

Also, I realised something really odd earlier today before I had this accidental breakthrough - I noticed that only the high pressure gauge was going down slowly when I turned off the tap (ie the gas trapped between the bottle’s tap and the reg was draining), but the low side was staying at whatever pressure I set it to. I have absolutely no idea how an issue with the post or disconnect could cause that. If you’re thinking that sounds like a gauge or washer leak, I would agree, except that I could literally watch the needle falling with the QD connected, then pull it off, and the needle would stop falling

If you have a small leak, then CO2 will flow through the regulator to keep at the set pressure. With the bottle turned off, you only have a very small volume of high pressure between the gas bottle and the regulator, so it wont take much flow through the reg to drop the pressure quickly on the high pressure gauge.

 

[starkers]

If you have a small leak, then CO2 will flow through the regulator to keep at the set pressure. With the bottle turned off, you only have a very small volume of high pressure between the gas bottle and the regulator, so it wont take much flow through the reg to drop the pressure quickly on the high pressure gauge.

Makes sense. In my head most of the mols were on the high pressure side so the low pressure side should drop faster once high pressure was depleted. But yeah, when I think about it it's like 40x more pressure on the upstream side but probably 1000s of times more volume in an empty keg then in the little section between tap and regulator

 

[MontPel]

Makes sense. In my head most of the mols were on the high pressure side so the low pressure side should drop faster once high pressure was depleted. But yeah, when I think about it it's like 40x more pressure on the upstream side but probably 1000s of times more volume in an empty keg then in the little section between tap and regulator

The high pressure and low pressure side are still connected when you close the gas bottle valve and you leave the regulator valve in the same position. If you have a leak downstream of the regulator then gas will flow from the small volume high pressure region through the regulator to the low pressure side. The low pressure gauge will not drop until the pressure in the high pressure side drops below whatever the low pressure is.