03. What is The Working Principle of a Screw Air Compressor?
A rotary screw air compressor is a type of positive displacement compressor where the compression of air is achieved through the varying volume of intermeshing helical rotors inside the compressor housing. The main and auxiliary rotors rotate within a precision-matched housing, creating cyclic changes in the volume between the rotor grooves. This allows for the intake, trapping, compression, and exhaust of air.
- Intake Process: As the rotors rotate, the volume between the main and auxiliary rotors gradually expands. This expanding volume is connected to the intake port, allowing external air to be drawn into the rotor cavities. The intake process ends when the volume between the rotors reaches its maximum and is disconnected from the intake port.
- Trapping and Conveying Process: Once the intake process is completed, the rotor profiles seal against the compressor housing, trapping the air within the closed chambers formed by the main and auxiliary rotors and the housing. This is the trapping process. The continued rotation of the rotors causes the rotor profiles to mesh, gradually moving the trapped air towards the discharge side. This is the conveying process.
- Compression and Oil Injection Process: During the conveying process, the volume between the rotor profiles decreases due to their intermeshing. This reduction in volume compresses the air, resulting in an increase in pressure. Meanwhile, lubricating oil is injected into the rotor grooves and mixes with the compressed air due to the pressure difference.
- Exhaust Process: When the volume between the rotors aligns with the discharge port of the housing, the compressed air begins to be expelled. This process continues until the tooth end profiles of the rotors completely mesh, reducing the volume between the rotors to zero and fully exhausting the air. This completes the exhaust process.
(a) Inhalation process (b) sealing and delivery process
(c) Compression and fuel injection process; (d) Exhaust process