Piston Compressors

Piston (reciprocating) compressors are the oldest and most versatile type of compressors. They use a piston moving inside a cylinder to compress air.

Operating Principle

The piston compressor works through the reciprocating movement of a piston inside a cylinder:

Intake:                      Compression:
    ┌─────────┐                 ┌─────────┐
    │  Valve  │ ←Air            │  Valve  │ →Compressed
    │  open   │                 │  open   │  air
    ├─────────┤                 ├─────────┤
    │         │                 │░░░░░░░░░│
    │         │                 │░░░░░░░░░│
    │    ↓    │                 │░░░█████░│
    │  ═════  │                 │░░░░░░░░░│
    │ Piston  │                 │  ═════  │
    └────┬────┘                 └────┬────┘
         │                           │
      Crankshaft                  Crankshaft

1. Downward stroke: Piston moves down, creating vacuum that opens intake valve
2. Filling: Atmospheric air enters the cylinder
3. Upward stroke: Piston moves up, compressing the air
4. Discharge: When system pressure is exceeded, discharge valve opens

Types of Piston Compressors

Various compressor designs: screw, two-stage piston, single-stage piston, rotary vane, and blowers.

Single Stage

• Compresses air in a single stroke
• Suitable for lower pressures (up to ~100 PSI / 7 bar)
• Simpler design
• Lower initial cost
• For intermittent use

Two Stage

• Compression in two successive cylinders
• Higher efficiency for high pressures (up to 175+ PSI / 12+ bar)
• Intercooling reduces temperature
• Better for continuous service
• Longer lifespan

Main Components

Component	Function
Cylinder	Chamber where air is compressed
Piston	Moving element that compresses air
Rings	Seal the gap between piston and cylinder
Valves	Control air inlet and outlet
Connecting rod	Connects piston to crankshaft
Crankshaft	Converts rotation to linear motion
Crankcase	Contains lubrication oil

Advantages vs Disadvantages

Advantages

Feature	Description
Versatility	Wide pressure range (up to 6,000 PSI)
Initial cost	Generally lower than other types
Simplicity	Easy to understand and repair
Availability	Wide variety of sizes and capacities
Portability	Compact designs available

Disadvantages

Feature	Description
Pulsations	Non-continuous flow
Noise	Higher than screw or scroll
Duty cycle	Limited (50-60% typical)
Maintenance	More frequent than other types
Vibration	Requires solid foundation

Ideal Applications

1. Small workshops - Intermittent use, low cost
2. Backup - When main compressor fails
3. High pressure - Where screw can't reach (>175 PSI)
4. Portable - Easy to transport
5. Frequent starts/stops - Handles cycles well

Duty Cycle

Piston compressors have a limited duty cycle. A compressor with 50% duty cycle should not operate more than 30 minutes per hour. Exceeding this causes overheating and premature failure.