As the compression of air continues, the reduced pockets of air are discharged through another area of the chamber. Screw compressors, which are also known as rotary screw compressors and are a specific style of reciprocating compressors, are ideal for large industrial applications because of their ability to provide continuous output over a long period of time. The two screws, or rotors, inside the screw compressor connect with each other as they circle around, and only allow space at certain times, which is what draws in, compresses and then releases the air.
The powerful bursts of air that result from this compression fuel many applications. Single cylinder screw compressors can be small enough to be portable, while multi cylinder systems are used in large industrial contexts. Screw compressors are commonly used for a variety of applications among construction, manufacturing, agriculture, food and beverage, mining and automotive industries.
They are also utilized in air tools, woodworking, pharmaceuticals, natural gas and plastics production. Air compressors are often made of aluminum, steel or cast iron, but are also occasionally made from plastic when a particularly light weight compressor is needed. The smaller components may also be made from plastic, although the nature of the screw compressor means that usually the insides of it are metal.
The effectiveness of screw compressors requires minimal space between the rotors and the air chamber so that the compression areas are properly sealed. Often, oil is used to facilitate this process and aid in sealing. The oil is then separated from the discharge stream, cooled, filtered and recycled. It is normal for some entrained compressor oil to carry over into the compressed gas stream and gradually seep into the surrounding air, which is not acceptable to the food and medical fields in particular.
That is why oilless air compressors are becoming popular, because they complete the air compression process without the aid of oil for cooling and sealing. The downside of oil-free screw compressors is that they have lower discharge pressure capability, but they are useful in situations in which oil carry-over cannot occur. Although they may be more costly initially, screw compressors have also been said to require less maintenance and have longer operating lives than other air compressors of comparable size, which is arguably reason enough to invest the money in a screw compressor versus another style.