Is the tank pressure gauge accurate while in fridge?

[exploding_monkeyface]

I just bought a regulator/CO2 tank combo (I used the cartridges and naturally carbonated in the past) and found out first hand that you need to check for leaks. I drained an entire 5lb tank overnight.

Back to the distributor to get the tank refilled.

Not one to repeat the same mistake I performed the soap test, I had to tighten down a couple of connections but no more bubbles.

My question is, my tank pressure gauge showed 55 when I first hooked it up. I now have my keg pressure at 30psi (to force carb) inside the fridge. Now that I'm paranoid about leaks, can I trust the tank pressure gauge to tell me if I'm losing CO2 to a leak? The gauge now reads ~50. Could that be caused by the cold forcing constriction of the gauge, the beer absorbing gas (it's only been about 2 hours) or do I have another leak I didn't detect?

 

[day_trippr]

There's a good chance the high pressure tank gauge is totally accurate - with respect to the tank temperature. To wit, follow the effect of temperature on the CO2 vapor pressure:

[edit] Note the chart is obviously in PSI while you were using BAR...
[edit2] If the curves are confusing, just look at the inset table...

Cheers!

 

[63belair]

I keep my C02 in the fridge and my experience has been that the high pressure gauge is only good for telling me my tank is kicked.

 

[thadius856]

I just bought a regulator/CO2 tank combo (I used the cartridges and naturally carbonated in the past) and found out first hand that you need to check for leaks. I drained an entire 5lb tank overnight.

Back to the distributor to get the tank refilled.

Not one to repeat the same mistake I performed the soap test, I had to tighten down a couple of connections but no more bubbles.

My question is, my tank pressure gauge showed 55 when I first hooked it up. I now have my keg pressure at 30psi (to force carb) inside the fridge. Now that I'm paranoid about leaks, can I trust the tank pressure gauge to tell me if I'm losing CO2 to a leak? The gauge now reads ~50. Could that be caused by the cold forcing constriction of the gauge, the beer absorbing gas (it's only been about 2 hours) or do I have another leak I didn't detect?

Assuming the temperature remains the lame, the high side gauge will show the same pressure until you have no more liquid CO2 left, at which point you're within the last 1% of the tank. You cannot trust it to indicate leaks.

For leaks, you can pressurize a hose, then turn off the shutoff on that hose and wait. When you flick it back on hours later, if the regulator groans at all, you have a leak on that hose.

 

[day_trippr]

Assuming the temperature remains the lame, the high side gauge will show the same pressure until you have no more liquid CO2 left, at which point you're within the last 1% of the tank.[...]

Actually, that's not accurate - as the chart above illustrates. You can follow the curves that show pressure as a function of temperature and %fill to see where the low side knee is.

You cannot trust it to indicate leaks.

That is true. Anything it shows would be way too late to be helpful on that count...

Cheers!

 

[thadius856]

Actually, that's not accurate - as the chart above illustrates. You can follow the curves that show pressure as a function of temperature and %fill to see where the low side knee is.

Okay, lets look at the graph then.

At 40F constant, from 135% rated fill all the way down to 15% rated fill, pressure is a constant 567 psi, at which point it dives.

So, no, not 1%. But the lesson is the same. Pressure doesn't drop until you're running on fumes.

Looking at the chart again, you can see that this pattern holds true for any properly filled tank stored at 82F or below. It starts diving earlier and less aggressively the higher temperature the tank is stored, but the thread title specifically says "while in a fridge".

 

[exploding_monkeyface]

After 24 hours it seems to be holding steady. I dropped the pressure from 30psi to 11psi, the pressure the all knowing carbonation chart shows for my temp/desired carbonation level. Now it's just wait and see. I'll update the thread on Friday when I try it.

Should I expect a perfect pour on the first beer or will the first couple of glasses be all foam?

 

[day_trippr]

Exactly. Taking the curve for, say, 40°F, the knee is considerably above the 1% level - more like 15%...

Cheers!

 

[thadius856]

Should I expect a perfect pour on the first beer or will the first couple of glasses be all foam?

Unless you have cold lines with cold beer already in them, cold shanks, cold faucets and a frosted mug for the first pour or two... a glass or two of foam. You can shorten the amount by getting a recirculating fan going to combat stratification.

 

[day_trippr]

[...]Should I expect a perfect pour on the first beer or will the first couple of glasses be all foam?

There's an assumption that the only problem was due to over-carbed beer. If that's the case, and you get that beer calmed down to the proper carbonation level for its temperature, you should get a good pour...

Cheers!

 

[mattd2]

Okay, lets look at the graph then.

At 40F constant, from 135% rated fill all the way down to 15% rated fill, pressure is a constant 567 psi, at which point it dives.

So, no, not 1%. But the lesson is the same. Pressure doesn't drop until you're running on fumes.

Looking at the chart again, you can see that this pattern holds true for any properly filled tank stored at 82F or below. It starts diving earlier and less aggressively the higher temperature the tank is stored, but the thread title specifically says "while in a fridge".

But there is a big difference though between 1 & 15%. Say a normal 5# tank last for 5 kegs. with 15% left you can still push over 1/2 a keg before it is empty. With 1% you would get less than 1/2 pint out from when it starts to drop to dead empty.
But you are correct that the "Pressure doesn't drop until you're running on fumes" after all that is the nature of a liquifiable gas