The co2 cylinder or compressed gas cylinder is the beginning of the pressure side of your draft beer system. Like a lot of the other parts of your system it may be a mystery to you.
Let’s look closely at this piece of equipment and try to take some of the mystery out of the co2 cylinder for you.
Although there are a few common problems that occur on the pressure side of your draft system, the gas cylinder is usually not one of them. Except when it is empty – no co2 no beer!
Since co2 is a natural part of the atmosphere and since it is a natural component of beer, it seems logical to use co2 to pressurize your draft system. How co2 provides the pressure to your system via the cylinder is important to understanding how draft beer works.
How Can So Much Gas Fit into Such a Small Cylinder?
By forcing co2 into the relatively small space of a typical gas cylinder the molecules are pushed closer and closer together. The result of this crowding of gas molecules together is less movement of the molecules in space – they are slowing down. In slowing down the molecules are also losing energy in the form of heat – they are getting colder.
At a pressure of about 880 pound per square inch, co2 loses enough energy and is cold enough to become a liquid. This is the form that it takes inside your gas cylinder. In this state far more co2 can fit into the cylinder than could as a gas at room temperature.
The key thing to note here is the pressure – 880 psi. It is this pressure that provides the push for your draft beer system. However, the cylinder is only storing the co2 at this pressure. Upon opening the cylinder a portion of the liquid evaporates (turns back to a gas) and is available to flow into the gas side of your draft beer system. When used, the high pressure of the gas is reduced by your regulator down to a more manageable level.
The co2 cylinder is usually made of aluminum for light weight and corrosion resistance and regardless of its size is fitted with a valve to turn on or off the flow of gas from the cylinder.
The valve opens by turning the valve handle or “hand wheel” counterclockwise and closing by turning it clockwise until it stops. There is also a pressure relief valve built into the body of the valve. This will automatically discharge the cylinder if the pressure exceeds a preset level.
The valve body has a threaded outlet that allows the attachment of a regulator.
Around the collar of the cylinder stamped into the body are a number of identifying characters.
They will look something like this:
DOT-3AL1800FXXXXXXX M4002 07C08 B20 U18 T25.2LB TC-3ALM124 T11.5KG CATALINA
Here’s what those markings represent:
DOT-3AL - The U.S. regulatory authority, the Department of Transportation (DOT), and specification, 3AL, to which the cylinder is manufactured in compliance.
1800 - The service pressure, in pounds per square inch (psi), of the cylinder.
FXXXXXXX - The serial number of the cylinder.
M4002 - The M-number or Manufacturers Number issued by the DOT to the manufacturer.
07C08 - The original hydrostatic test date of the cylinder, month followed by year, performed at the time of manufacture of the cylinder. The C represents the symbol of the Independent Inspection Agency (IIA) performing the inspection of and certifying the acceptance of the cylinder at the time of manufacture.
B20 - The cylinder identifier (product name). It identifies the market, "B" for beverage, and capacity "20" for a capacity of 20 pounds of CO2 charge, of the cylinder.
U18 - The cylinder outlet thread designation as specified in CGA TB-16.
T25.2LB or TW25.0LBS - The tare weight (in lbs.) of the empty cylinder package.
TC-3ALM - The Canadian regulatory authority, Transport Canada (TC), and specification, 3ALM, to which the cylinder is manufactured in compliance.
124 - The service pressure of the cylinder expressed in metric units, bars.
CATALINA - The name of the manufacturer of the cylinder.
T11.5KG - The metric tare weight (in kgs) of the empty cylinder package. The empty cylinder package includes the cylinder, the valve, the carrying handle and the snap ring.
Note: not all cylinders will have all of these markings.
When refilling cylinders the filling service will inspect your cylinder for damage and the last hydrostatic test date. If the cylinder has not been hydrostatically tested in five years they may not fill the cylinder. If it is damaged they also will not fill it.
The cylinders come in a number of sizes. For your ease of use stick with 2 1/2, 5, 10, 15 or 20 pound cylinders. You will be storing, moving and transporting these cylinder so you want to consider that when purchasing a new cylinder.
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