A rotary-screw compressor employs two helical screws or rotors to compress air. A female rotor and male rotor are used. Although the rotors feature different shapes, they are made to precisely fit one another. When the rotors begin turning, the air is sucked in and pushed to the pressure side of the rotors. In turn, new air is sucked into the components. Because this process is continuous, the compressor runs quietly.
Some of the Amenities
Compared to piston-type compressors, the screw compressor is more expensive. However, the rotary-screw compressor operates 24/7, 365 days each year. That makes it ideal for manufacturing environments that want to reduce any downtime. The screw compressor’s capacity is usually much larger when compared to piston types. If you need a good deal of air in your factory, this kind of compressor is the best choice.
Oil-free and Oil-injected Compressors
Rotary-screw compressors are sold in oil-free versions and oil-injected models. Whether the compressor runs on oil or not, the principle is the same. Rotors push the air to the side. The difference lies in the design of the compressor elements, or where the actual compression occurs.
As you might surmise, the oil-injected machine cannot operate without oil whilst the oil-free compressor does not require oil. Therefore, the rotors employed in the oil-free compressors are considered to be of a superior quality. They display very little space between them; however, they do not come into contact with each other either. Otherwise, a problem with wear would surface. As a result, the rotors used for oil-free compressors can be very expensive.
That being said, the oil-injected models are used more frequently anyway. Oil-free compressors are used for special applications. Most of the oil-free models are employed in large food factories or chemical refineries where the air must be totally oil-free. Otherwise, the chemical process, product, or food could become contaminated.
How Oil-injected Rotary Compressors Work
Oil-injected rotary compressors operate when oil is injected into the element where the compression occurs, or during the actual compression. Later, the oil is removed by an oil separator. The air that is compressed then is clean.
Although almost all of the oil remains in the compressor, the oil, in some rare instances, may pass through the separator and leave the compressor with the air that is compressed. This type of issue is known as an oil carryover. Therefore, oil-injected compressors are not designed to create oil-free air and therefore cannot be employed in facilities where oil-free air is required.
A Way to Prevent Rust
For most of the factories that use compressors, a small oil-carryover is not considered a problem. In fact, users of the compressors note that the small oil-carryover prevents rust, helping the machines run more smoothly.
The Benefits Associated with Using a Rotary-Type Compressor
The advantages of using a rotary air compressor are as follows:
- Quiet operation
- High volume of air at a continuous flow
- Lower energy cost when compared to a piston-type compressor
- Can be used 24/7
The drawback of using the rotary air compressor is the cost as it is more expensive than a piston compressor, and it may produce oil carryover.