For a kegerator owner there is nothing more frustrating than going to pour a beer from the tap and your (just filled) CO2 cylinder is empty. This has happened to me countless times and the air leak seems to always originate from a different place than the time before. I've just accepted that this is part of kegerator ownership, but you can run through a list of common leak points after you hookup a new tank (cylinder) of CO2 to reduce the chance of total tank loss, depression and dry mouth.
First thing to do is get a spray bottle and fill it with some soapy water to perform a leak test. You can also use a no-rinse sanitizer like Star San mixed with water if you are a homebrewer. You just need something that will bubble up when air is escaping. I use about 8 oz of water and a quick squirt of dishwashing soap, shake it up in the bottle and you are ready to spray.
I like to isolate sections of the draft system to troubleshoot leaks. Start your spray test at the CO2 tank. With the keg removed from the system and your regulator set to zero pressure, open your CO2 tank top valve. Start spraying where the regulator nut meets the CO2 tank post. If you find bubbles here, you can attempt to tighten the nut or install a CO2 leak stopper. If all is OK here, just keep working your way down the system until you find some bubbles.
Apply some low pressure (2-3 psi) to the regulator with the hose valve closed and spray around the regulator gauge threads. This checks the threaded connections for small pinhole leaks. Next, open the hose valve to allow air down the lines to the keg coupler (for commercial kegs) or quick disconnects (for homebrew kegs). Spray all clamp connections on hoses and look for leaks. I have found these are the most common points for leaks and it usually just requires a quick tightening of the clamp to fix the issue.
To continue the test, connect your keg and spray all the connections to look for bubbles. If you have multiple kegs make sure you spray down the air splitter (distributor) manifold and all the threaded and clamp connections looking for bubbles. If the leak persists you should check your faucet and all the seals inside.
To make sure you have fixed the leak, apply 10 psi to the entire draft system for 15 -20 minutes. Record the starting tank level from the regulator and then again after the test is completed. If you see a difference then you still have a leak and need to keep hunting.
Knowing you can dispense 4 or 5 half barrels of beer with a full 5 lb cylinder of CO2, it is important to check your system for leaks and fix them. Filling a CO2 tank is usually around $40, so it is not only frustrating to lose a whole tank of CO2 it is also expensive to keep refilling it. Below is an exhaustive list of all the areas in a draft system you could find air leaks.
The hose can get cut or pinched by the clamp if you tighten it down to hard causing a leak. Tighten the clamp or snip off the old portion of hose and reconnect. Use metal clamps for the best results.
Leaks can occur through the lever screw if loose and also through the threads if no Teflon or plumber's tape is used. You must wrap the threads in Teflon (plumber's tape) and make sure the screw on the valve lever is tight.
A common leak occurs where the regulator and CO2 tank come together. Nylon or fiber washers are used as a gasket in the connection point, but sometimes leak if you don't get them on just right and cranked down extremely tight. You can also use an inexpensive no-fail part from Beverage Elements called the CO2 leak stopper as an alternative.
The CO2 safety valve is rarely the culprit, but in some cases where your tank is very old or was dropped it can be the source of a leak if not seated correctly.
CO2 gauges are usually installed tight at the factory, but in some cases where you modify or drop a regulator the gauges can become loose and cause air leaks. Threaded pressure gauges must be wrapped in Teflon (plumber's tape) and tightened down into the regulator. You can also add some CO2 gauge protectors to cushion the blow if the tank falls over.
A loose top nut on your CO2 cylinder valve handle won't leak air, but you should always keep it tight so it doesn't accidentally come off and cause you to drop the tank.
Sometimes gaskets get old and brittle and just can't do their job anymore. Get new gaskets if this is the source of the air leak.
These o-rings can become brittle and cause your keg to leak air, draining your CO2 tank slowly over time.
These gaskets can also become worn out over time and can cause air leaks. It is recommended to use Keg Lube on homebrew keg post gaskets to keep them from getting damaged.
It is very common for these seals to fail after extended use and cleaning with chemical cleansers.
All threaded connections should have Teflon tape and the lever screws should be tight. You can submerge the entire unit in soapy water to help find small pinhole leaks in the manifold.
It is very common for these faucet seals to fail after extended use and cleaning with chemical cleansers. Disassemble your faucet and check seals for wear.
Not a usual suspect, but an old Sanke (commercial) keg coupler seal or skirt can get worn down and nicked over time. It is recommended to use keg lube on the gasket to keep it from becoming brittle.
In some cases a regulator can leak from an internal issue. Some regulator models have rebuild kits that come with replacement parts to get you up and running again without having to buy an entire regulator. Micro-Matic and Taprite have a nice selection of repair and rebuild parts for CO2 regulators. The first thing to attempt is a simple cleanout procedure.