A rotary air compressor works by trapping air in a chamber and mechanically reducing its volume using rotating components. The most common type is the rotary screw compressor, which utilizes two intermeshing screw-like rotors.
Here's a breakdown of the working principle, focusing on the widely used rotary screw type:
The Core Principle: Trapping and Compressing Air
Unlike piston compressors that use reciprocating motion, rotary compressors use continuous rotary motion to compress air. In a rotary screw compressor, this is achieved by two helical rotors (often called male and female rotors) that rotate in opposite directions inside a chamber.
Stages of Operation
The compression process in a rotary screw compressor typically involves three main stages:
- Intake: Air enters the compression chamber through an intake valve. As the rotors turn, they create a space between their lobes and the housing. This space increases, drawing air in.
- Compression: As the rotors continue to turn, the lobes mesh, trapping the air in the pockets between the rotors and the housing. The point where the lobes mesh moves along the length of the rotors towards the discharge end. This action progressively reduces the volume of the trapped air pocket, causing the pressure to increase.
- Discharge: When the compressed air pocket reaches the end of the rotors, it aligns with a discharge port, and the compressed air is expelled from the compressor.
The Role of Oil in Rotary Screw Compressors
Many rotary screw compressors are oil-injected. Oil plays several crucial roles:
- Lubrication: It lubricates the rotors and bearings, reducing friction and wear.
- Sealing: It helps seal the gaps between the rotors and the housing, as well as between the rotors themselves, preventing air from leaking back and ensuring efficient compression.
- Cooling: The compression process generates heat. Oil absorbs much of this heat, helping to maintain optimal operating temperatures and protecting the compressor components.
According to the reference: Oil is injected directly into the valves (meaning into the compression process area, often near the intake or along the rotors) to ensure lubrication and help with sealing and cooling.
Oil Separation Process
After compression, the discharged air is a mixture of compressed air and oil mist. This mixture needs to be separated before the air can be used.
As stated in the reference: Most of that oil is removed in the air receiver/oil separator. Through centrifugal action, the oil particles are separated from the compressed air. The mixture enters the separator, and the swirling motion causes the heavier oil particles to be thrown against the walls, where they collect and drain away (typically back into the oil circuit after cooling and filtering). The cleaner, compressed air exits the separator ready for use.
Key Components
| Component | Function |
|---|---|
| Rotors (Screws) | Intermesh to trap and compress air. |
| Housing | Encloses the rotors and forms the compression chamber. |
| Intake Valve | Controls air entry. |
| Discharge Port | Allows compressed air to exit. |
| Oil Injection System | Injects oil for lubrication, sealing, and cooling. |
| Air Receiver/Oil Separator | Separates oil from compressed air (using centrifugal action). |
Benefits of Rotary Screw Compressors
- Continuous Airflow: Provides a steady supply of compressed air without pulsations.
- Compact Design: Generally smaller for a given output compared to reciprocating compressors.
- High Efficiency: Especially at full load.
- Reliability: Fewer moving parts than reciprocating compressors, leading to high durability.
In summary, a rotary screw compressor compresses air by trapping it between two rotating screws and reducing its volume. Oil is injected during this process for lubrication, sealing, and cooling, and is subsequently removed from the compressed air using a separator, often employing centrifugal force.
