Rotary screw compressors are just one of a variety of air compressors. They employ a rotary type positive expulsion system, which conveys pressurized air to power drills, pumps and other types of machinery. Rotary screw compressors, also known as positive displacement compressors, deliver a determinate amount of highly pressurized air.

Rotary screw compressors contain the following components, all enclosed in a sealed case: the compressor unit, systems that maintain proper lubrication, proper temperature control, proper capacity control and the system that cleans the discharged air. Inside of the compressor unit itself there are two interlocking corkscrew-shaped augers or rotors. Each auger or screw has a wide end and a narrow end. The wide end of the screw is the inlet that allows free air to flow into the screw housing upon demand, helped along by the partial vacuum caused by the screws rotating inside the housing.

The air and oil combination flows downward from the wide ends to the narrow ends of the screw. This increases the vacuum, pulling more air into the housing. As the mixture is pulled downward through the grooves of the auger, the space where the air was narrows. At the narrow end of the screw, a valve tunnels the condensed air and oil into a separator, removing as much oil as possible from the condensed air. It is then released into the compressor receiver.

Rotary screw compressors are available in oil cooled and oil free. When comparing the oil cooled model to the oil free model, the procedure for compressing the air is basically the same, although the medium in which the procedure is carried out is different. One is performed in an oil filled chamber which provides coolant and sealant properties. The byproducts of the oil filled units are gas and oil instead of air and oil, which are the byproducts of the oil free systems. Oil free rotary screw compressors work the same except that in the absence of the oil the process does create higher temperatures and it is less energy efficient.

When choosing a rotary screw air compressor there are some important things to remember and take into consideration. What type of project are you working on? Does your compressor need to be transportable? Do you want oil cooled or oil free? Many consumers report that rotary screw compressors are easy to maintain and have a long life. They are known for their above average production abilities in a small package.

Using compressed air as an efficient kinetic energy resource requires a simple machine and holding tank. All compressors will have the same basic parts: receiving tank, pressure gauge and compression machinery. The identifying difference between two-stage and single-stage compressors is the number of compression cylinders incorporated.

Single-stage air compressors follow a few simple principles. When the compressor’s piston is actuated it literally squeezes the air contained inside its cylinder until the PSI is strong enough to release a one-way valve connection between the cylinder and the receiving tank. As the piston cycles, the receiving tank is filled with compressed air. A pressure switch is located on the receiving tank to regulate the tank's maximum PSI with a mechanical relief valve attached for safety purposes. When the set maximum air pressure is achieved in the tank, a switch connected to the pressure switch will signal the motor to turn off. The pressure inside the receiving tank is continually monitored by the pressure gauge. When the PSI in the receiving tank drops below a preset level, the pressure switch will activate the motor to add more compressed air to restore the overall pressure of the receiver.

A two-stage air compressor follows the exact same principles as the single-stage but there are two actuating pistons. The first stage will produce compressed air at a lower pressure than is ultimately desired for the end use. As the pressure in the first receiving stage builds it supplies air to the second stage's cylinder. The air is again compacted before being released into the output receiving tank. The advantage of a two-stage compressor is that it distributes the work load between two components to achieve a higher level of compressed air without having to overwork a single piston. The higher PSI offerings of two-stage compressors make them the better choice for industrial use and high torque pneumatic tools.

A single-stage compressor is a highly efficient machine. Choosing an oil-less type will ensure long use with little maintenance required. The disadvantage to a single stage compressor is that its output is limited to providing air below 125 PSI.

Two-stage compressors require slightly more maintenance because they have more parts. The advantage is that greater PSI offerings can be efficiently maintained without over-exerting the machine. Two-stage compressors also generate less heat than single-stage compressors do, which means that parts may not wear out as quickly and your compressor will likely have a longer life.