CO2 weight question

[puckjer]

so i have been troubleshooting some CO2 leaks lately. i was curious...i weighed a full 5lb CO2 cylinder and it came in at 15.2 lbs. i hooked it up to my 5 gal commercial keg (already carbed) and to my 5 gallon corny keg that i just syphoned a new batch of homebrew in. so essentially it is just carbing the homebrew. both guages are set to about 12 psi. i purged the homebrew keg a couple of times and let it sit overnight. this morning i wanted to check the weight of the cylinder to see how much gas had gone out since my last cylinder only lasted 3 weeks(i had a leak but never really could identify it). the weight of the cylinder this morning was 14.6 lbs. so in a 12hr period the tank lost .6 lbs. that seems like a lot to me but that may be normal for carbing a new beer. i would like to hear what others have experienced with that type of thing.

 

[WrongCoastBrewery]

You could assume some of the losses are to the absorbtion of CO2 into the carbing beer. Stuff has to go somewhere. Still, you may have a very slight leak somewhere. Get a spray bottle of sanitizing solution and spray down all of your connections to check. My guess would be from a poppet on the gas out post or the relief valve. Those seem to always be my leaky spots.

 

[puckjer]

i have leak tested just about everything and cant find one anywhere but i know i had one since my last cylinder only lasted 3 weeks. the only bubbling i could see on corny keg was around the gas in post but it was very small. i went ahead and replaced that o ring which was in pretty bad shape. the only 2 other places that could be leaking would be the gas Quick disconnect (will check that tonight by submerging it) or on my sankey tap or commercial keg. the reason i suspect the sankey/commercial keg is that i hooked up that keg about the same time i started having the leak. that sankey has been through 3, 5 gallon kegs with no issues so far. no leaks showing on the sankey when i sprayed so i was wondering if there is a leak in the rubber gasket where it couples to the keg itself.

at what point should i not see notable drops in tank weight when carbing a new keg at 12psi? i would think the pressure would more than likely equalize after a couple of days with only very small drops after that since most of the CO2 is being injected in the first 12 hrs or so.

 

[WrongCoastBrewery]

You would be surprised how much CO2 can be wasted on those post leaks. Your carbing beer will continue to absorb CO2 until it reaches saturation. That can take up to two weeks depending on the temperature and pressure. There is a good thread sticky on this:

https://www.homebrewtalk.com/f35/keg-force-carbing-methods-illustrated-73328/

Or it could be the Sankey keg. Give those connections a good spray down to check.

 

[puckjer]

i think i am going to disconnect the sankey and then re-seat it. is it common practice to use keg lube on the rubber seal on the sankey? i never used it on the first 3 kegs i went through. just trying to cover all my bases. is it also common to use keg lube on the o-rings at the top of each post where the quick disconnects sit?

i realize that it could take up to 2 weeks to fully saturate the homebrew, and that is a great article. i would just assume that the bulk of the CO2 used in the carbing process would be in the first 12 hrs since you are purging, and then adding CO2 where none was present to begin with. after that is done it should only take very small amounts over the 2 weeks to saturate the beer.

 

[Bobby_M]

Yes, most of the absorption occurs sooner than later because the partial pressure differential is greatest at that time. Over a half a pound of CO2 in 12 hours seems like quite a bit but if you did purge a lot, it might be OK.

I'm going to throw out some really rough numbers and if anyone has any better ones, let me know.

CO2's density at 0C and 1 ATM (per wiki) is about 2 grams per liter. One volume of CO2 (which I assume is achievable in 12 hours at 12psi) for 5 gallons is about 19 liters. 12psi on the regulator is close enough to 2ATM for my napkin math so figure the density of the CO2 is closer to 4 grams per liter. So, 4 grams x 19 liters is 76 grams or 2.6 ounces. That's assuming your beer actually achieved 1 volume of carbonation in 12 hours. I'd expect a keg to use up about half a pound of liquid CO2 to reach 2 volumes of CO2, after about 2 weeks, prior to dispensing any beer.

I'm really bad with physics and math though so I'm probably blowing serious smoke.

 

[WrongCoastBrewery]

I have never used keg lube on a sankey connection. I do however use it when I rebuild my cornies. You could use it though if you think the seal is in need of some extra help.

True, that a good portion of the CO2 is absorbed initially (like a dry sponge in water). If there is any pressure differential, gas will flow. Hence any leak is bad since it causes a small differential and gas will flow to the path of least resistance.

 

[JonW]

FYI - leaky poppits are only a concern when NOT attached to Co2 or bev out connectors. Once you put a ball lock connector on the post, the poppit is pushed down and the seal is not utilized. At that point, the exterior o-ring on the post is what is sealing. Keep the exterior o-rings lubed.

 

[puckjer]

checklist for tonight...
1)re-weigh cylinder to see if it has lost any more weight since 7am this morning
2) unhook, lube rubber seal, and re-seat sankey on commercial keg
3) lube exterior o-rings on the posts

hopefully this will solve any issue i may be having.

 

[Thirteen]

i have leak tested just about everything and cant find one anywhere but i know i had one since my last cylinder only lasted 3 weeks. the only bubbling i could see on corny keg was around the gas in post but it was very small.

One neglected area to check is the connection between the tank and regulator. It can be hard to leak check because of the size of the coupling which can hide a slow leak.

 

[WrongCoastBrewery]

One neglected area to check is the connection between the tank and regulator. It can be hard to leak check because of the size of the coupling which can hide a slow leak.

Indeed. Especially if you are using the paper gasket they give you. I think mine was teflon coated and I tossed the paper one that came with it.

 

[puckjer]

well i checked everything yesterday evening and the tank hasnt lost any more weight so i guess the leak was fixed by changing that o-ring on the gas in post. yayyyyy, i should have yummy Dunkel ready in a week or so.