Leaky keg driving me mad...

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monkeydan

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Hi all,

I have searched, read, watched videos, etc. etc. but need some help...

I have a corny keg which will not hold pressure (tested using spunding valve).

So far I have done the following:

- Replaced all o-rings (2 on gas post, 2 on beer post, 1 on lid)
- Lubed all o-rings with keg lube
- Wound PTFE (teflon) tape around gas and beer post threads and re-tightened
- Sprayed everything with soapy water (no bubbles)
- submersed entire keg in water (no bubbles!!)

I removed the spunding valve after pressurising the keg in case this was the culprit, but when I reattached it, the keg had still had lost pressure (from 12 PSI to 9 PSI over 3 hours or so).

I know CO2 will go into solution and pressure is expected to drop slightly even if keg is not leaking, but would you still expect a drop like this??

The leak is way slower since I wrapped the threads with PTFE tape but is still dropping.

Not sure where I go from here?! THERE ARE LITERALLY NO BUBBLES!!! AAAAAARGH!!!!

Any other suggestions??

I have a new lid (just in case!) and a new keg on the way but it would be great to be able to have this one in service if possible.

Thanks :)
 
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monkeydan

monkeydan

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Thanks for that.

Forgot to mention that I also replaced some of the poppets!

The universal ones don't seem to fit all my posts, so one post got a new one and one didn't... I can order some new posts but they're weird dimensions and cost about 3 x as much as newer ones. (I tried to replace the posts already but the new ones I have don't fit; they're not deep enough).

Maybe I should just bite the bullet and get new posts too?! Although with the cost of the new lid as well, I may as well just buy another keg!!
 

Closet Fermenter

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How about the pressure relief valve? The only keg leak I have had was there, and it is even easier to change than the o-rings.
But, the no soap bubbles is a head scratcher. 🤷🏼‍♂️
 

tracer bullet

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I'd consider checking again after maybe 24 hours or so. Be sure you're not seeing some sort of pressure change with temperature. I'd guess that if anything it'd sit and increase in pressure a bit after a fill but just to be completely sure.
 

bracconiere

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The universal ones don't seem to fit all my posts, so one post got a new one and one didn't..


i got a tip from someone here a while back, that some posts need the unis to be snipped a ring shorter to fit..


is this a pin lock, or ball lock keg? pin locks use bigger o-rings? but you say it lost pressure with nothing hooked up.... 🤔

which poppet didn't get replaced? maybe fill it with some water to see if it starts oozing out the bev post? i've been surprised to find my crisper drawer in my fridge to be full of beer a few times before....
 
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Deadalus

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i got a tip from someone here a while back, that some posts need the unis to be snipped a ring shorter to fit..


is this a pin lock, or ball lock keg? pin locks use bigger o-rings? but you say it lost pressure with nothing hooked up.... 🤔

which poppet didn't get replaced? maybe fill it with some water to see if it starts oozing out the bev post? i've been surprised to find my crisper drawer in my fridge to be full of beer a few times before....
unis? Did you mean springs?

@monkeydan Is this a new to you keg? Can you read the writing and maybe tell us the manufacturer? You mentioned new posts not being deep enough. Some posts have a plastic insert that could be missing making the posts short. Although your old ones allegedly fit so probably not the issue. Also, what temperature is the keg at? Is it inside a fridge or something?
 

marc1

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I know CO2 will go into solution and pressure is expected to drop slightly even if keg is not leaking, but would you still expect a drop like this??

So the keg is full? If the beer is not carbed, then pressure will be going into solution. I'm not sure how fast, but a few PSI over a few hours doesn't seem impossible.

I recommend transferring the beer to a good keg, then troubleshooting this one. That will also keep your beer safe while this gets worked on.
 

Deadalus

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So the keg is full? If the beer is not carbed, then pressure will be going into solution. I'm not sure how fast, but a few PSI over a few hours doesn't seem impossible.

I recommend transferring the beer to a good keg, then troubleshooting this one. That will also keep your beer safe while this gets worked on.
Yeah if it is really full, the CO2 will dissolve in rather quickly as there isn't much CO2 in the headspace. I burst carb,--higher PSI than force carbing--and I will turn off the CO2 to that keg so that I can serve the rest. When I come back again, full kegs will take more CO2 to where you can hear it going in. This will happen more than once if I don't shake and move around the keg. I can't really move a keg around too vigorously inside the keezer due to depth. This was why I was asking the temperature of the keg, because they were only using 12 psi to begin with. If the keg was warm, it would go into solution pretty readily.
Sometimes I burst carb kegs over a period of 2 days or so and still only get out weakly carbed beer. Not a lot of headspace and I didn't have the tank on and probably needed more frequent bursts. I much prefer to let the keg sit at the forced carb pressure over a week or longer. I just installed three new secondary regulators so I can leave the primary alone and make each keg happy.
 
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monkeydan

monkeydan

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How about the pressure relief valve? The only keg leak I have had was there, and it is even easier to change than the o-rings.
But, the no soap bubbles is a head scratcher. 🤷🏼‍♂️
I swapped out the PRV for a new one, but the new one leaked so I put the old one back again! Doesn't seem to be the PRV as there are no bubbles, but there are no bubbles anywhere which is why I am indeed scratching my head 🤔

If you can pressurize the keg submerged in a bathtub full of water and look for bubbles.
I did do this... No visible bubbles at all. It was only at 10 PSI, you reckon I should crank that sucker up a bit?!

i got a tip from someone here a while back, that some posts need the unis to be snipped a ring shorter to fit..


is this a pin lock, or ball lock keg? pin locks use bigger o-rings? but you say it lost pressure with nothing hooked up.... 🤔

which poppet didn't get replaced? maybe fill it with some water to see if it starts oozing out the bev post? i've been surprised to find my crisper drawer in my fridge to be full of beer a few times before....
It's a ball lock, all the new o-rings looked to be the same size as the old ones... No idea which poppet did and didn't get replaced, I was working on two kegs at the same time and just got everything mixed up 😄

Might see if snipping some of the spring off will allow the poppet to fit.

@Deadalus it's not a new keg to me or (new in general!) It's a 'Safer' brand keg. Keg is just in the garage which is quite cool, maybe 55-60 F or so?

@marc1 yes, the keg is full... Sadly with water 😄. I didn't want to waste a bunch of gas filling an empty keg just to pressure test it! It's up to the weld line so quite full.

I guess to be absolutely sure I could dump the water and fill with gas.

My new lid arrived today so I'm doing another test but the keg is still full of water (did it before I read all the replies!)

If the pressure still drops slowly, I'll do a test with gas only and then if it STILL drops then I will pay some more attention to the posts, poppets etc.
 

Deadalus

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I have never heard of that brand before. I see that you are in the UK. I only found one reference to that brand name and it was an unanswered thread here at HBT. The OP says their keg had unusual pin lock posts and the poppet was leaking. Kegs come with different parts so in the future, it's always a good idea not to mix up the parts. Lids are mostly similar and interchangeable but there are racetrack style lids that have a different oval shape. Although I wouldn't mix them up because sometimes they work on one keg and not the other. Used kegs are really temperamental, once I get one working I don't mix them up.

At that temperature, if it were beer, you would reach 1.77 - 1.89 volumes of CO2. It would take several days though. Those are on the low side. I suspect beer and water are similar in solubility for CO2 but don't know. The level of carbonation in soda is generally higher than in beer, around 3-4 for soda. It may have dissolved just a little and you weren't noticing it. I agree about testing it empty. It's not too hard on the CO2 but I will say I have a 15 gallon keg I was testing and it took more time it seemed to fill. I was going to try your trick with the water actually but I am reconsidering after this discussion!
 

doug293cz

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...

I removed the spunding valve after pressurising the keg in case this was the culprit, but when I reattached it, the keg had still had lost pressure (from 12 PSI to 9 PSI over 3 hours or so).

I know CO2 will go into solution and pressure is expected to drop slightly even if keg is not leaking, but would you still expect a drop like this??

...
Yes, a 3 psi pressure drop over 3 hrs for a keg filled with water is pretty much what I expect for CO2 absorption. So, leak testing by pressure gauge with a filled keg will not work (unless you fully carbonate whatever is in the keg first.)

A keg holds about 20 liters, so if you fill it with 19 liters (~5gal) of water, you have about 1 liter of headspace. CO2 has a density of roughly 2 g/L at atmospheric pressure, so at 12 psi the density will be:
Density = 2 * (14.7 + 12) / 14.7 = 3.6 g/L, and at 9 psi it drops to:​
Density = 2 * (14.7 + 9) / 14.7 = 3.2 g/L​
Since the headspace is 1 L, you went from 3.6 g of CO2 in the headspace to 3.2 g, for a "loss" of 0.4 g of CO2.

A "volume" of carbonation corresponds to about 2 g/L of CO2 in solution. If you started with uncarbonated water, and added 0.4 g of CO2, that only brings the CO2 level in the water up to:
CO2 level in water = 0.4 g / 19 L = 0.021 g/L, and the carbonation level to:​
Volumes of carbonation = 0.021 g/L / 2 g/L = 0.01 volumes​
The equilibrium carbonation level at 9 psi and 60°F is 1.54 volumes, so your water could absorb a lot more CO2 before your keg would not appear to be leaking.

Brew on :mug:
 
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Mutant

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My most frustrating leaks were actually flaws in the keg posts. Once the posts were replaced I solved the problem. I had gone through all the typical changes of o-rings, but they didn't solve the problem. I could never identify exactly what was wrong with the posts, but they were flawed.
 
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monkeydan

monkeydan

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Yes, a 3 psi pressure drop over 3 hrs for a keg filled with water is pretty much what I expect for CO2 absorption. So, leak testing by pressure gauge with a filled keg will not work (unless you fully carbonate whatever is in the keg first.)

A keg holds about 20 liters, so if you fill it with 19 liters (~5gal) of water, you have about 1 liter of headspace. CO2 has a density of roughly 2 g/L at atmospheric pressure, so at 12 psi the density will be:
Density = 2 * (14.7 + 12) / 14.7 = 3.6 g/L, and at 9 psi it drops to:​
Density = 2 * (14.7 + 9) / 14.7 = 3.2 g/L​
Since the headspace is 1 L, you went from 3.6 g of CO2 in the headspace to 3.2 g, for a "loss" of 0.4 g of CO2.

A "volume" of carbonation corresponds to about 2 g/L of CO2 in solution. If you started with uncarbonated water, and added 0.4 g of CO2, that only brings the CO2 level in the water up to:
CO2 level in water = 0.4 g / 19 L = 0.021 g/L, and the carbonation level to:​
Volumes of carbonation = 0.021 g/L / 2 g/L = 0.01 volumes​
The equilibrium carbonation level at 9 psi and 60°F is 1.54 volumes, so your water could absorb a lot more CO2 before your keg would not appear to be leaking.

Brew on :mug:

I cannot thank you enough, this is super helpful and I really appreciate you taking the time to explain it.

It has been a long time since I did any physics. Or maths. Or anything academic really 😄

Can I ask where the value of 14.7 comes from?? Couldn't figure it out, doesn't seem to be related to the volume of the headspace or density of the gas etc. 🤔

Thanks again.
 
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monkeydan

monkeydan

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I have dumped the water and filled the keg with CO2 only @ ~13 PSI with the new lid in place. Definitely holding firm for the time being but will check back in a few hours.

Appreciate all the responses 😊
 

jerrylotto

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So it sounds like you may have a wonky lid seal. If it sometimes holds and sometimes doesn't, keg lube the big lid O-ring and make sure that both mating surfaces (lid and keg) are flat and clean.
 

MicroMickey

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I had a keg that was driving me nuts with a slow leak. I wound up filling it about 3/4 full of plain water and gassing it up. I then submerged it in a tub of water and looked for the culprit leak. It was easily found and dealt with.
 

max9

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One time I had a gas leak I had trouble finding. Turned out it was post itself that had a tiny crack in the metal…. a manufacturing defect I guess. Replaced the post and problem fixed.
 

doug293cz

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I cannot thank you enough, this is super helpful and I really appreciate you taking the time to explain it.

It has been a long time since I did any physics. Or maths. Or anything academic really 😄

Can I ask where the value of 14.7 comes from?? Couldn't figure it out, doesn't seem to be related to the volume of the headspace or density of the gas etc. 🤔

Thanks again.
Standard pressure - atmospheric pressure of air in psi
We have a winner! Whenever you are doing calculations with gas pressures, temperatures, absorption, etc., you have to work with the gas's absolute (rigorously partial) pressure. Gauges measure the difference between atmospheric pressure and absolute pressure (total partial pressures of all the gases in the mix), so you have to add atmospheric pressure to gauge pressure before doing any calculations. Carbonation charts and calculators have this gauge to absolute conversion hidden under the covers.

I have dumped the water and filled the keg with CO2 only @ ~13 PSI with the new lid in place. Definitely holding firm for the time being but will check back in a few hours.

Appreciate all the responses 😊
Glad we have solved your mystery, and your keg appears to be holding.

Brew on :mug:
 

Dgallo

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I also didn’t notice anyone discuss or ask in regards to temperature changes, just incase it wasn’t due to something this simplistic. Glad to hear your problem is solved
 

doug293cz

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I also didn’t notice anyone discuss or ask in regards to temperature changes, just incase it wasn’t due to something this simplistic. Glad to hear your problem is solved
The pressure drop going from 68°F (20°C, 293.15°K) to 32°F (0°C, 273.15°K) is:

New P = Old P * 273.15 / 293.15, and the delta is:​
Delta P = Old P - Old P * 273.15 / 293.15​
Original pressure was 9 psig or 14.7 + 12 = 26.7 psia, so the delta would be:
Delta P = 26.7 * (1 - 273.15 / 293.15) = 1.8 psi​
OP didn't have anywhere near that temp swing, so temp change cannot explain the ~3 psi pressure drop. All you need to explain the pressure drop is CO2 absorption by the water.

Brew on :mug:
 
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monkeydan

monkeydan

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Hi all, you will be delighted to hear that pressure in my keg is holding firm ☺️

I did definitely have a leak (originally pressure was dropping by several PSI in minutes) but whatever I did actually fixed it, I just didn't realise 😄

Now I know not to fill the keg with anything other than gas when pressure testing!

Thanks again for help, suggestions and physics lessons 👍🏻
 
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