A reciprocating compressor is a positive-displacement compressor that uses pistons driven by a crankshaft to compress gases. It is widely used in industries for high-pressure gas compression.
1. Working Principle
A reciprocating compressor works similarly to a piston engine but in reverse:
Intake Stroke
The piston moves downward, creating a vacuum that opens the inlet valve.
Gas enters the cylinder.
Compression Stroke
The piston moves upward, compressing the gas.
The inlet valve closes, and pressure builds.
Discharge Stroke
At a set pressure, the discharge valve opens, releasing compressed gas.
Return Stroke
The piston resets, and the cycle repeats.
PV Diagram of a Reciprocating Compressor
Suction (1-2): Gas enters at constant pressure.
Compression (2-3): Pressure rises as volume decreases.
Discharge (3-4): Compressed gas exits at high pressure.
Expansion (4-1): Residual gas re-expands before the next cycle.
2. Types of Reciprocating Compressors
(A) Based on Design
| Type | Description |
|---|---|
| Single-Acting | Compression occurs only on one side of the piston. |
| Double-Acting | Compression occurs on both sides (higher efficiency). |
| Diaphragm Type | Uses a flexible diaphragm instead of a piston (for corrosive/clean gases). |
(B) Based on Stages
| Type | Description |
|---|---|
| Single-Stage | Compresses gas in one step (up to ~100 psi). |
| Multi-Stage | Uses multiple cylinders for higher pressures (up to 5000+ psi). |
(C) Based on Drive Mechanism
Motor-Driven (Electric) – Common in industrial applications.
Engine-Driven (Diesel/Gasoline) – Used in remote locations.
3. Key Components
Cylinder – Where compression occurs.
Piston – Moves back and forth to compress gas.
Crankshaft & Connecting Rod – Converts rotary motion into reciprocating motion.
Valves (Suction & Discharge) – Control gas flow.
Intercooler (in Multi-Stage) – Cools gas between stages for efficiency.
4. Advantages & Disadvantages
✅ Advantages
High Pressure Capability (up to 5000+ psi in multi-stage).
Wide Range of Gases (air, refrigerant, hydrogen, etc.).
Better Efficiency at Low Flow Rates compared to centrifugal compressors.
❌ Disadvantages
Pulsation & Vibration (requires damping systems).
High Maintenance (valves, piston rings, seals wear out).
Limited Flow Rates (not ideal for high-volume applications).
5. Applications
Oil & Gas Industry (CNG compression, gas pipelines).
Refrigeration & HVAC (ammonia, Freon compressors).
Chemical Plants (hydrogen, nitrogen, oxygen compression).
Power Plants (air compression for pneumatic systems).
6. Reciprocating vs. Rotary vs. Centrifugal Compressors
| Feature | Reciprocating | Rotary Screw | Centrifugal |
|---|---|---|---|
| Pressure Range | Very High (5000+ psi) | Medium (150 psi) | Low-Medium (200 psi) |
| Flow Rate | Low-Medium | High | Very High |
| Efficiency | High at low flow | Moderate | High at high flow |
| Maintenance | High | Low | Medium |
| Applications | High-pressure gas | Industrial air | Large HVAC, turbines |
Conclusion
Reciprocating compressors are ideal for high-pressure, low-to-medium flow applications but require more maintenance than rotary or centrifugal compressors. They remain essential in industries like oil & gas, refrigeration, and chemical processing.
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