A compressed air tank, or "carry tank," is a handy workshop or garage tool that allows you to store compressed air in a portable, easy-to-use unit. You fill up the tank with compressed air, using any type of air compressor, then carry the tank to wherever you need it. Compressed air tanks are most commonly used for filling up tires—on cars, bicycles, trailers, ATVs, etc.—but they're also useful for applications using a blow-off tip. The tanks typically are too small for operating air tools for more than a few quick operations.
Its relatively light weight and large size make a portable compressed air tank more useful in the field than a portable air compressor in many situations. For example, if you need compressed air in any remote location where there's no electricity to run a compressor, you can fill up an air tank at home (or at a gas station or hardware store on your way out) and carry it into the field. The compressed air tank is much lighter than an air compressor with a similarly sized tank, and it's much bigger than the tanks on highly portable compressors, such as pancake compressors.
Compressed Air Tank Sizes and Ratings
Compressed air tanks come in different sizes, with capacities measured in gallons of compressed air. Common sizes include five, seven, nine, 10, and 11 gallons. A 10-gallon or larger size is likely to be more useful for a variety of applications, while a small five- or seven-gallon tank is highly portable and takes up less space.
To estimate how the tank capacity translates to practical air volume, keep in mind that 7.5 gallons of tank volume equal one cubic foot of volume. A small car tire has a volume of approximately one cubic foot. That means a seven-gallon air tank does not have quite enough capacity to fill a small car tire that's completely flat.
In addition to capacity, compressed air tanks have a maximum pressure rating measured in pounds-per-square-inch or psi. Common ratings range from 125 psi to over 150 psi. This rating indicates the maximum amount of air pressure the tank can safely handle. However, it's a good idea not to fill the tank to its maximum pressure level, because air pressure increases with heat. So, for example, if you leave a tank in the sun the pressure inside the tank will rise even without adding more air. If the tank is completely full, the pressure could exceed the rated maximum pressure and cause a rupture.
Portable Compressed Air Tank Components
The components of a portable compressed air tank provide all the features you need for easy and safe use. You'll typically find the following components on these tools:
- Air fill valve: The valve that you connect to when filling the tank with a compressor.
- Air shutoff valve: A knob that turns to prevent air from leaking out of the tank when it's not in use.
- Air pressure gauge: Indicates the air pressure inside the tank as well as how full the tank is.
- Pressure tank: The pressure-rated tank that holds the compressed air.
- Flexible hose: The hose for delivering compressed air from the tank. Hoses may attach to the tank with a threaded fitting or a quick-connect fitting.
- Universal fitting: Some tanks include a universal quick-connect fitting to allow easy changes of hose types.