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. 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. The tanks typically are too small for operating air tools for more than a few quick operations.
What Is a Portable Compressed Air Tank?
A compressed air tank is a pressure vessel that holds air compressed under pressure. It releases this air on an on-demand basis through the use of a valve. Though some air tanks might be stationery, they can also be portable.
Parts of a Portable Compressed Air Tank
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 compressed air
- Flexible hose: the hose for delivering compressed air from the tank, which may attach with a threaded fitting or a quick-connect fitting
- Universal fitting: a universal quick-connect fitting to allow easy changes of hose types
When filling a portable compressed air tank, watch the pressure gauge carefully. You never want the pressure to exceed the manufacturer's recommendation. You'll also want to underfill the tank a bit to allow the air to expand with heat without worry of potential rupture of the tank.
How to Use a Portable Compressed Air Tank
Understand the Sizes
Compressed air tanks come in different sizes, with capacities measured in gallons of compressed air. Common sizes include 5, 7, 9, 10, and 11 gallons. A 10-gallon or larger size is likely to be more useful for a variety of applications, while a small 5- or 7-gallon tank is highly portable and takes up less space.
Estimate What Size You Need
To estimate how the tank capacity translates to practical air volume, keep in mind that 7.5 gallons of tank volume equal 1 cubic foot of volume. A small car tire has a volume of approximately 1 cubic foot. That means a 7-gallon air tank does not have quite enough capacity to fill a small car tire that's completely flat.
Consider the Rating
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.
Choose and Fill Your Compressor
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 by using an air compressor; if you don't have one, you can use the compressor at a gas station or hardware store. Simply attach the fill nipple to the tank and use the compressor as you normally would to slowly fill the tank, watching the pressure gauge to be certain the pressure doesn't rise too quickly or too high.