How a Rotary Screw Air Compressor Works

Picture of a Rotary Screw Air CompressorThere are many types of air compressors on the market today, many of which are specifically designed for special purposes, but others that are appropriate to a wide range of application. However, today the rotary screw air compressor is the most popular type on the market and the most widely used across various industries and applications. Although the rotary screw air compressor comes in many different forms, the most popular by far is the dual-screw compressor, which uses two screws as opposed to single screw or multi screw options.

Inside most dual screw rotary screw air compressors there are two screws, a female one and a male one which rotate in opposite directions through a series of synchronization gears. The driving power typically comes through the female screw, which transfers this power to the male one, turning it. While the threads of the two screws are interlocking, they do not in fact touch one another, instead they get gradually closer to one another the further they run, but never actually contact each other.

As these two interlocking screws rotate, air is drawn into them through an inlet port and is transferred into the space between the two interlocking – but not touching – screws. As the two screws rotate, they gradually reduce the amount of volume available to the trapped air between the screws and the housing of the compressor. This reduced space puts the air under pressure. Eventually the air reaches the end of the two screws and is expelled through the output, or exhaust, valve.

Although there are many rotary screw compressor varieties that do not use oil, most of them do in fact use oil today as it helps prevent the escape of air and at the same time collects and removes other particulate matter from the air that is expelled. For oil based systems, increasing amounts of oil are added to the air and in between screws as the air goes down the length of the screws. In order to separate the oil, the output valve leas to a separator unit which separates the oil from the air, with the air being expelled through an output hose and the oil is recycled back through the compressor.

Although the use of oil is widespread and preferred for many applications, it is also inappropriate for many others. The problem is that no existing separator unit is able to fully remove all of the oil from the air, so at least some oil particles are present when the air is expelled through the output hose. Needless to say, in any application where having oil traces is a problem, the oil based rotary screw air compressor is not appropriate. Examples of this include compressed air meant to be breathed (scuba tanks, oxygen used by fire and medical personnel, and others) or air that is used in the production of extremely sensitive electronics (like circuitry and conductors). For this reason, there is also a good selection of rotary screw compressors that do not use oil at all, though these are typically less efficient.

There are also many other variations on the basic theme of the rotary screw air compressor, but they all use the basic positive displacement method described above. Rotary screw air compressors have come to dominate the industry specifically because they are very effective and require considerably less maintenance than many alternative types of compressor.


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