29/03/2025
What is Rotary Screw Air Compressor?
A Rotary Screw Air Compressor is a positive displacement compressor that generates compressed air by using two intermeshing helical rotors (screws) to reduce the volume of air. It is designed for continuous-duty operation, offering high efficiency, durability, and stable air delivery—making it a workhorse in industrial settings.
Technical Explanation
Working Principle:
The rotary screw compressor works on the principle of internal compression. Air enters the inlet and is trapped between the rotating male and female screws. As the screws turn, the air is pushed along the threads and its volume decreases, causing pressure to rise. The compressed air is then discharged through the outlet.
Main Components:
| Component | Function |
|---|---|
| Rotors (Male/Female) | Helically cut screws that interlock and compress air as they rotate. Typically made of steel, with precision-machined profiles. |
| Air End (Compressor Block) | Housing that contains the rotors and supports compression. |
| Inlet Valve | Regulates the flow of air entering the rotors. Can be load/unload or modulation type. |
| Oil System (for oil-injected types) | Cools, seals, and lubricates the rotors. |
| Separator Tank | Separates oil from compressed air before delivery. |
| Cooling System | Includes air/oil coolers to maintain proper operating temperatures. |
| Drive System | Typically electric motor + belt or direct gear drive. |
| Controller (PLC/HMI) | Monitors pressure, temperature, service intervals, and controls operation modes. |
Operating Cycle (Oil-Injected Type):
- Air Intake – Ambient air enters through the inlet valve.
- Compression – Air is trapped and compressed between the rotating screws.
- Oil Injection – Oil is sprayed into the air to seal, cool, and lubricate the rotors.
- Separation – Compressed air and oil are routed to a separator tank.
- Cooling – Air and oil are cooled by separate coolers.
- Air Delivery – Dry compressed air is sent to downstream systems.
- Oil Recirculation – Oil is filtered and reused.
Key Technical Specifications:
| Parameter | Typical Range |
|---|---|
| Working Pressure | 7 – 15 bar (100–220 psi) |
| Capacity (FAD) | 0.5 – 100+ m³/min |
| Power Rating | 5 – 500+ kW |
| Duty Cycle | 100% continuous operation |
| Noise Level | 60–75 dB(A) (with enclosure) |
| Cooling Type | Air-cooled or water-cooled |
Types of Rotary Screw Compressors:
| Type | Description |
|---|---|
| Oil-Injected (Lubricated) | Most common; oil used for cooling, sealing, and lubrication. |
| Oil-Free | Air and rotors never contact oil; used in food, pharma, electronics industries. |
| Variable Speed Drive (VSD) | Adjusts motor speed to match air demand; highly energy-efficient. |
Technical Advantages:
- High Efficiency: Continuous air delivery without pulsation
- Low Maintenance: Fewer moving parts than reciprocating compressors
- Durable: Long lifecycle with proper maintenance
- Compact Design: Higher output per footprint
- Low Vibration & Noise: Especially with enclosures
Common Industrial Applications:
- Automotive assembly lines
- CNC machine shops
- Pharmaceutical manufacturing
- Textile factories
- Food & beverage production
- Pneumatic automation systems
