What is restriction?
When dispensing keg draft beer, the goal is to keep the CO2 level prescribed by the Brewer. Any change in the CO2 level will alter the taste, pouring characteristics and appearance of the beer. Most breweries in the U.S. recommend a CO2 pressure between 12-14 lbs for Ale & Lager types of draft beer. This CO2 pressure will maintain the level of carbonation specified by the brewery.
Beer hose is used to transport the beer from the keg to faucet and is also used to control how fast the beer pours from the faucet. The way this works is the length and inner diameter (I.D.) of the beer hose is calculated to "balance" against the CO2 pressure that is applied to the keg. This controls the beer flow and assures the beer dispensed from the faucet is neither too fast nor to slow. This is called "restriction" and the more restriction added to a system the slower the beer flows from the faucet.
For example, most beer towers have a 5' length of (3/16” I.D.) vinyl beer hose. This is because this size and length of tubing is the appropriate restriction for most keg refrigerators being dispensed with 12-14 lbs of CO2 pressure.
In applications where the distance between the keg and faucet is greater than 5' a larger size (I.D.) of hose should be used to balance the system. This is because 3/16” I.D. vinyl beer hose longer than 5' would cause the beer to flow too slowly, too much restriction is in the system for the amount of CO2 pressure. In some systems the CO2 pressure is then increased to overcome the restriction, although the beer will flow faster it is likely to become over-pressurized, resulting in foamy beer.
To assure the best glass of draft beer Micro Matic recommends setting the CO2 pressure to the Brewers specification and controlling the flow rate with the proper length and diameter of beer hose.