A portable tire inflator is a compact air compressor that is generally small enough to be carried by hand. They are typically battery powered or run on 12-volts DC, in which case they can have alligator clips to connect to a car battery or a plug to connect to an auto's cigarette lighter. The main purpose of a portable tire inflator is to adjust the air pressure in car tires while out on the road. Some units are powerful enough to inflate a completely flat tire to the specified pressure, while others are only capable of inflating to a level where neither rim or tire will be damaged while seeking repairs.
Portable tire inflators come in a variety of configurations, sizes, and capacities. The simplest units typically contain only a compressor, a mechanical pressure gauge, and are powered by 12-volts. They will often only be able to run for a limited amount of time before the compressor must be allowed to cool off, and have an upper limit on what PSI (kPa) they can inflate a tire to. Smaller units will generally have a lower limit and overheat more quickly, while providing the benefit of being easier to stow away in a small trunk or under a seat.
Combination inflators may also be widely available. These units may combine a portable tire inflator with a number of other complimentary functions. They might have a bright lamp attached in case a tire goes flat at night, flashing red or orange lights to warn other vehicles of a breakdown, an emergency siren, or a variety of other options. Some units that are battery-powered may also include jumper cables. These often have a powerful gel-pack battery on board, and can be used to jump start cars with dead batteries.
Certain units will include other useful features, like an automatic shutoff. These inflators are typically able to run for a prolonged period without overheating and include a dial or other mechanism to set a desired air pressure. They can then be attached to the schrader valve on the tire, turned on, and will later turn off automatically when the correct pressure has been reached.
In addition to pumping up car tires, a portable tire inflator can often be used to inflate other things. Many of these portable compressors will either come with a variety of attachments or be compatible with attachments obtained separately. In these cases, a portable tire inflator may be used to inflate things like bicycle or lawn mower tires, sports balls, and even beach toys.