If you've ever had to inflate the tires on your car or bicycle, you've had firsthand experience with an air compressor. Air compressors can be found in gas stations and manufacturing plants, as well as home workshops and garages. Smaller versions can be used to inflate pool toys or even run power tools such as nail guns, sanders, drills, wrenches, staplers and spray guns.
Reducing the size of the space that contains the air increases air pressure. This space is called the air tank, and it is set to hold a certain amount of air at a specific pressure. A conventional compressor also has a crankshaft, a connecting rod and piston, a cylinder and a valve head (see diagram). The crankshaft is powered by an electric motor of gas engine. As the piston moves down, it creates a vacuum that allows outside air to push open the valve and fill the area above the piston. As the piston moves up, the air above it compresses. This holds the valve shut while air is pressed into the tank. With each stroke, more air enters the tank, and the pressure rises. The motor turns on and off as needed to maintain pressure in the tank.
Some car manufacturers, like Zero Pollution Motors in France, are developing air-powered cars that operate on the same principle. Compressed air is stored in tanks at high pressure. This air is then fed through an air injector to the engine and flows into a small chamber, which expands the air. As it expands, the air pushes down on the pistons and moves the crankshaft, which gives the vehicle power. Such engines can either run on compressed air alone, or serve as a regular internal combustion engine.