Home brewers are forced to choose between ball lock or pin lock keg systems early on in their brewing careers.
Cornelius kegs are the remnants left to us of the old method of carbonating soda, the one that replaced the "soda jerk". Now, soda companies use plastic bags instead of kegs and their old Cornelius kegs have fallen into the hands of home brewers. As it turns out, two rival companies used two different fittings in the manufacture of their kegs, making the keg system almost interchangeable. The two systems are known as ball-lock and pin-lock. Both systems serve the same function, but home brewers are forced to choose one system or the other early on in their brewing careers. Here, I will discuss the differences between the two.
Both the ball-lock and pin-lock systems have two ports coming out of the keg. One port has a short tube leading down into the liquid, and this is the "gas-in" port. The other port has a long tube leading all the way to the bottom of the keg. This is the "Liquid-out" port.
How It Works
The CO2 gas enters through the "gas-in" port, filling up the top of the keg with pressure. This pressure is applied directly to the liquid, forcing it up into and out of the "liquid-out" port.
In the ball-lock system, the fittings on top of the keg are slightly different from each other. This difference is hard to tell unless you look closely at the two. The "gas-in" fitting will only work with a matching gas fitting, not with a liquid line fitting. This can cause some consternation if you take apart your keg to clean it - the port fittings look very much alike. If you put the wrong fitting on the wrong side, you may have trouble dispensing your beer. This is the main argument against ball-lock fittings, but the problem is easily avoided if you know about the difference between the two fittings that, at first, look to be the same.
Pin-lock systems use a style of fitting in which the "gas-in" and "liquid-out" fittings are also different. To differentiate the two, the pin-lock system uses two and three pin port fittings. The pins of these fittings fit into slots on the gas line and liquid line fittings. The "gas-in" line has two pins, while the "liquid-out" has three pins. This is intended to prevent the gas from simply bubbling up through the drink without dispensation.
While pin-lock Cornelius kegs are built so that they cannot possibly be fitted backwards, they are less common than ball-lock kegs. This is an important factor when looking at which system to invest into. Parts will be more easily found for the ball-lock kegs than the pin-lock kegs. Then again, the pin lock kegs go together a little more easily after cleaning. For most home brewers, the decision between ball-lock and pin-lock kegs is highly influenced by which system they find first when bargain hunting! An influence that is more practical than any other consideration, as far as we can tell.
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