Air compressors work in two phases: the compression operation and the release operation. There are multiple methods of compressing air, including reciprocating pistons, rotary screws and centrifugal compression. Compression release, or air delivery, varies as well, and is measured in cubic feet per minute. Generally, the more horsepower a compressor is capable of, the more powerful the air delivery.
Air Compression Methods
Positive-displacement compressors are the more common type of air compressors available for hobbyists, small-scale applications and industrial-scale applications, although other types, including rotating impeller compressors, are still commonly used. A positive-displacement compressor essentially relies on part of the device performing an intake of air, and then minimizing the amount of space in the chamber to pressurize the air molecules. When the air is released, a valve opens and the compressed air quickly discharges.
Piston-type compressors are fairly common. These compressors use the motion of a piston to introduce air into a chamber through an intake valve. An automotive-type piston is a clear example. An automotive-type piston consists of a crankshaft connected to a rod, which is topped by a cylinder inside another cylinder. The crankshaft base revolves in a small circle. The connecting rod remains in a fixed position in relation to the crankshaft, but it operates in a hinged manner with the cylinder, allowing the cylinder to remain vertically or horizontally oriented at all times. When the crankshaft is at its lowest revolution point, the rod drops the cylinder as well. When the crankshaft turns further, the rod rises, pushing the cylinder up. This constant motion perpetuates an up-and-down path for the cylinder, and allows for air intake and release.
The exterior cylinder is topped with an inlet port, an outlet port and two valves housed in three chambers. One chamber is the inlet chamber, one chamber is the outlet chamber, and between them is the pistons cylindrical chamber. When the piston drops, the inlet port allows air to fill the space in the cylindrical chamber through an inlet valve. When the piston rises, the inlet port does not allow air to pass back through into the inlet chamber, so the air travels through the outlet valve into the outlet chamber. The repetition of this process forces more and more air into the outlet chamber, causing more compression. When the user releases the outlet chamber, air delivery occurs.
Other positive-displacement compressors use a different method of compressing their air chambers. Rotary screw compressors create an air chamber between helical screws and their housing. When the screws turn, the air chamber volume reduces, compressing the air between the screws. Vane compressors consist of a slotted rotor within a slator, the fixed housing area for the rotor. Because of the blade orientation on the rotor, the rotor revolution pushes air into a chamber and works to compress the volume with each subsequent blade rotation.
Most all positive-displacement compressors use oil as a lubricant for compressor motion as well as a solid seal for the compressed air. All of these devices must account for this oil introduction by removing oil before release. If the oil isn’t separated from the compressed air, contamination may occur in the form of “oil carryover.”
A non-positive-displacement compressor example is a centrifugal compressor, which uses dynamic compression in operation. A centrifugal compressor spins an impeller, a type of rotor, to accelerate the air within, and then a diffuser to decelerate the air. This deceleration causes the pressure on the air to rise. This air heats up during the process and must be cooled by an intercooler.
Air Compressor Applications
Air compressors are used in a variety of commercial and industrial applications. Typically, commercial air compressors are designed to work with various tool attachments in order to provide pneumatic power. A variety of electric tools use the air compressor, including blo-guns, nail guns, air staplers, air sanders, spray guns and sandblasters. These tools usually have industry standard attachments so they can be hooked up to a variety of air compressor brands. Air compressors can also be used to fill tires and other items with air.
Industrial strength air compressors are used to power industrial tools much like commercial varieties, but they can also be used to power larger machines and applications. For instance, petroleum is often “coked,” when carbon particles known as coke are introduced to change the behavior of the petroleum for efficiency reasons. In order to coke large amounts of petroleum, air compressors are used to power the process. Air compressors are also used in applications where purging systems are required to remove unwanted particles.