CO2 Volume Loss or Leak

[palobrewer]

Hi,

I started kegging for the first time a couple days ago and I have a question regarding the loss of CO2. I'm not sure if I still have a leak or the Co2 is being absorbed into the gas.

Any comments or suggestions would be greatly appreciated.

Day 1

I wanted to force carb the keg in my mini fridge with 30 PSI for 24 hours, however, after 12 hours I check the regulator and it had lost 20 Bar of CO2. Started at 60 Bar then went down to 40 Bar of co2. So I believe this was a leak

Day 2

I took the Co2 out of the fridge and the gauge slowly went up to 48 Bar of Co2. I used the soap water test and found some joints that were bubbling and tightened everything again.

Day 3

I placed the Co2 tank back in the fridge and the following morning I read the gauge and it's around 40 Bar of co2.

Setup
- Mini-Fridge at 37 degrees F
- 3 Gallon Ball Lock Corny Keg
- 5 Lb Co2 Tank
- Taprite Dual Gauge MFL Regulator
- John Guest Fittings
- 3/8" Nylon Braided Tube

 

[dyqik]

CO2 in the tank is liquid, not gas. The pressure in the tank does not indicate the amount of CO2, which is mostly liquid, but the vapor pressure over the liquid in the tank. Until the liquid runs out, the pressure will stay the same at constant temperature. You can't use the high side pressure to indicate the amount of CO2 until the liquid runs out. You have to weigh the tank to measure the weight of liquid in it. This is the same as for propane tanks, by the way.

Colder CO2 has a lower equilbrium vapor pressure than warm CO2, so the pressure in the tank will go down as the CO2 in it cools down in the fridge. If the temperature of the tank is changed, then that's the reason for the pressure drop. The equilibrium vapor pressure is about 40 bar at 278K (5C, 41F) and 57 bar at 293 K (20C, 69F).

What can happen is that a big leak or CO2 use results in some of the CO2 liquid boiling off to replace the gas lost, and that boiling lowers the temperature in the tank, lowering the pressure. If the tank's environment doesn't change temperature, then a pressure drop means that CO2 is coming out from the tank. But here, I'd assume that the pressure drop is due to the tank being in a colder environment, as small leaks and CO2 being dissolved into the beer wouldn't be enough to make a noticeable difference.