Study of Construction and Working of Reciprocating, Rotary, Scroll, Wobble & Swash Plate Compressors
In the ITI Refrigeration and Air Conditioning (RAC) trade, compressors are the heart of refrigeration systems. Understanding different types of compressors, their construction, and working principles is essential for students and technicians. This chapter explains five important types of compressors: reciprocating, rotary, scroll, wobble plate, and swash plate compressors.
1. Reciprocating Compressor
Construction
- Cylinder and piston arrangement
- Crankshaft and connecting rod
- Suction and discharge valves
- Electric motor
- Crankcase and lubrication system
Working
The reciprocating compressor works on a piston-cylinder mechanism. When the piston moves downward, low-pressure refrigerant vapour is drawn into the cylinder through the suction valve. During the upward movement, the refrigerant is compressed and discharged through the discharge valve at high pressure.
This cycle repeats continuously, making it suitable for domestic refrigerators and small air conditioning systems.
2. Rotary Compressor
Construction
- Cylindrical casing
- Rotor mounted on shaft
- Sliding vane
- Suction and discharge ports
Working
In a rotary compressor, a rotor rotates inside a cylinder. The sliding vane maintains contact with the cylinder wall, forming a sealed chamber. As the rotor turns, refrigerant is trapped, compressed, and pushed towards the discharge port.
These compressors are compact, efficient, and widely used in split air conditioners.
3. Scroll Compressor
Construction
- Fixed scroll
- Orbiting scroll
- Motor and drive mechanism
- Sealed casing
Working
The scroll compressor uses two spiral-shaped scrolls. One scroll remains fixed while the other orbits around it. Refrigerant gas is trapped between the scrolls and gradually compressed as it moves toward the center, where it is discharged.
Scroll compressors provide smooth and quiet operation with high efficiency, making them suitable for modern air conditioning systems.
4. Wobble Plate Compressor
Construction
- Drive shaft
- Wobble plate mechanism
- Multiple pistons and cylinders
- Suction and discharge valves
Working
In a wobble plate compressor, the wobble plate is connected to a rotating shaft. As the shaft rotates, the wobble plate moves in a wobbling motion, causing multiple pistons to reciprocate within their cylinders.
This design allows multiple compression strokes in one rotation, increasing efficiency. These compressors are commonly used in automotive air conditioning systems.
5. Swash Plate Compressor
Construction
- Inclined swash plate
- Drive shaft
- Multiple pistons arranged axially
- Valve plate assembly
Working
The swash plate is mounted at an angle on the rotating shaft. As the shaft rotates, the swash plate converts rotary motion into reciprocating motion of pistons. Each piston compresses refrigerant in its cylinder.
These compressors are compact and capable of handling multiple cylinders simultaneously, making them suitable for automotive and high-capacity systems.
Comparison of Compressors
| Type | Motion | Efficiency | Application |
|---|---|---|---|
| Reciprocating | Back and forth (piston) | Moderate | Domestic refrigeration |
| Rotary | Rotational | High | Split AC |
| Scroll | Orbital | Very high | Modern AC systems |
| Wobble Plate | Reciprocating (multi-piston) | High | Automobile AC |
| Swash Plate | Reciprocating (axial) | High | Automobile & industrial AC |
Conclusion
Understanding the construction and working of different compressors is essential for RAC students. Each type of compressor has its own advantages and applications depending on system requirements.
Reciprocating compressors are widely used in domestic systems, while rotary and scroll compressors are preferred for modern air conditioning systems. Wobble and swash plate compressors are commonly used in automotive applications. Proper knowledge of these compressors helps in installation, servicing, and troubleshooting of refrigeration systems.