Checking for Draft System CO2 Leaks – Using The Pressure Gauge Method

Part of Our Homebrew Tips and Tricks Series.  Check out the complete list – Homebrewing Tips, Tricks & Shortcuts!

For the most part, checking for keg liquid and CO2 leaks is pretty straightforward.  Is beer leaking?  Then you’ve got a liquid leak.  Is there six inches of beer in your kegerator?  That one’s really easy to spot.  If beer is shooting out like a geyser, you’ve got a… fast leak. 🙂

For kegerator CO2 leaks, it’s a generally a little more work, but still pretty easy… spray everything with Star San [via Amazon] solution (diluted of course) and look for bubbles.

A problem spot.  There is one place on the CO2 side that the soak-everything-with-Star-San method doesn’t really work…. the keg’s gas post.  Testing at this point using the spray bottle method is impossible (or at the very least difficult and messy).  Unless your poppet is messed up, leaks will only surface here when a gas QD is actually engaged.  The problem is, you can’t easily see that spot when a QD on.  Stated more simply, you need a QD on to see if it’s leaking, but you can’t see it if a QD is on.

Enter what I call the “pressure gauge method”.  The pressure gauge method can check the entire keg including gas QD connection and any connected tubing without soaking everything and the resulting clean up.

My process for that…

  • Charge your keg with CO2 as usual.  Use your usual serving pressure.  Over-pressurizing can mask leaks that may otherwise show themselves.
  • Remove the CO2 line and replace with a pressure gauge or Spunding Valve – with the adjustable PRV set to a very high pressure so that not gas escapes.
  • After the pressure has stabilized. I mark the current pressure with a wax pencil, or you can just remember what it reads
  • Wait for a couple hours to overnight to see if the gauge drops.
  • If it drops quickly, there is a leak someplace in the system.  Note: If your keg has beer in it that is uncarbonated the pressure will drop some overnight (it is equalizing and carbonating the beer).  What you don’t want is a quick drop in pressure.
  • This technique tests the entire keg including the gas post, o-ring, QD and any tubing that’s connected.
  • In my experience, over long periods of time there will be some slow gauge movement.  I don’t know if these are micro leaks or temperature related, but I’m not really concerned with that, I am looking for a relatively quick drop in pressure.  Something that shows up within a couple hours.

This technique also has the advantage of saving Star San and saving some clean up that’s required when you soak gear in Star San.

If the CO2 gauge method indicates a leak, you can start spraying with Star San to hunt it down.  If you cannot find the leak, I would suggest changing your gas post o-ring to see if that’s the culprit.  I’m quick to replace o-rings, especially on the gas side.  I have lost a couple full tanks of CO2 to a bad gas post o-ring.  These typically cost just pennies [See: Bulk Keg Orings and Keg Repair Part Numbers].  I would much rather be safe that sorry when it comes to the time, cost and inconvenience of replacing an empty CO2 tank.  After you change the gas o-ring, re-check using the pressure gauge method.

This is one of the many uses of a Spunding Valve – See: Build a Spunding Valve.  You can also buy a simple gauge [See: Ball Lock QD Adjustable Pressure Valve W/Gauge via MoreBeer] or make a gauge assembly for this purpose.

I’m not suggesting this as a replacement for the Star San spray method.  Practically speaking, I use it as a complement to that to test an otherwise difficult to check spot.  I use the spray method when I keg a beer and use the pressure gauge method periodically or if I otherwise suspect a problem.

Related Gear and Resources…

Another option if you don’t have a spunding valve or other gauge (but do have a two gauge regulator) is to attach only one keg to your regulator and turn off the the CO2 tank.  This allows you to use the low pressure gauge to monitor the keg.  The benefit of this method is that you’re testing everything – line, manifold, QD, o-ring and keg.  The downside is you’re taking other kegs offline and it somewhat complicates things as you’re testing more than just the keg in question.

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