The CO2 regulator is the heart of your system. A CO2 regulator is used to step your CO2 tank pressure from 500 - 1200 PSI down to a much more reasonable 5 - 12 PSI. CO2 regulators come in many different varieties and configurations and the one you need depends entirely on your setup and future plans.
Welding Regulators Most welding regulators are designed to flow high volumes of CO2 for shielding gas and they will not regulate down to the pressures you need for your kegerator. These regulators will not work for a homebrew kegerator.
Pre-set Regulators Pre-set regulators come with the pressure pre-set and no gauge to monitor the CO2 pressure. These regulators can not be fine tuned without special tools will not work for a homebrew kegerator.
High Pressure CO2 Regulators These regulators typically come with a 0 - 160 PSI low pressure gauge, which can be hard to read in the 5 - 12 PSI range. But they work well and are usually a great value.
Low Pressure CO2 Regulators These regulators typically come with a 0 - 60 PSI or 0 - 50 PSI low pressure gauge and are easy to read since the gauge is usually marked every 1 or 2 PSI . These types of regulators are usually purchased for home as well as commercial keg setups.
Single gauge versed double gauge CO2 Regulators Single gauge regulators are the lowest cost solution but they do not have a gauge to display your CO2 tank pressure. Double gauge regulators are really a better value even though they usually cost a few dollars more because you can tell from the second gauge (the tank gauge) when you are about to run out of CO2.
Primary and secondary CO2 Regulators A primary regulator will connect directly to your CO2 tank while a secondary regulator needs the initial pressure dropped by a primary regulator. If you are setting up a simple 1 or 2 keg system then you only need a primary regulator. But if you are interested in serving several beers of several styles and / or a soda then a system composed of a primary and several secondary regulators is worth looking at. With this system, you would set your primary regulator to somewhere between 50 PSI and 150 PSI. Then you would connect your secondary regulators to the primary regulator and set each to its own individual pressure. If you only need 2 pressures then a 2 pressure regulator set is a better solution.
Draft beer Regulators verses homebrew beer regulators The difference between a draft beer regulator and a homebrew beer regulator is not the regulator itself. The difference is the CO2 out fitting. Draft systems almost always use a 3/8" or 5/16" gas line which means that you will need a CO2 regulator with a 3/8" barb fitting. 3/8" and 5/16" gas lines will both fit a 3/8" barb fitting. Homebrew systems are usually based on soda kegs and these systems almost always use 1/4" gas line and you will need a CO2 regulator with a 1/4" barb fitting. A third option is a regulator with a 1/4" flare (threaded) fitting which can be adapted to either standard with a simple fitting.
2 pressure CO2 Regulators 2 pressure regulators are really just 2 primary regulators connected together. The regulators are 100% independent of each other and each can be set to its own unique pressure. More than 2 regulators can be connected together but 3 or more becomes unstable and could tip over your CO2 bottle. With a 2 pressure regulator, you can run one draft keg and one homebrew keg or you can run one pressure for serving and another higher pressure just for fast carbonating your next homebrew keg of beer.
My Preference? I like the 2 pressure CO2 regulator with 1/4" flare (threaded) outputs because this gives me the most flexibility for the least amount of money.