Gas Behavior
Understanding how gases behave is fundamental to working with compressed air.
Air is a Gas
Air consists of particles in constant motion - this kinetic energy is what we harness in pneumatics.
Kinetic Theory
Gas molecules are in constant random motion. This motion:
- Creates pressure when molecules collide with walls
- Increases with temperature
- Decreases with volume expansion
Factors Affecting Pressure
1. Temperature
| Temperature | Effect |
|---|---|
| Higher temperature | More molecular motion → Higher pressure |
| Lower temperature | Less molecular motion → Lower pressure |
Practical example: Tire pressure increases after several miles of driving when the air heats up from friction.
2. Volume
| Volume | Effect |
|---|---|
| Smaller volume | More collisions per area → Higher pressure |
| Larger volume | Fewer collisions per area → Lower pressure |
3. Amount of Gas
| Amount | Effect |
|---|---|
| More molecules | More collisions → Higher pressure |
| Fewer molecules | Fewer collisions → Lower pressure |
How to Increase Pressure
Three methods:
| Method | How it works |
|---|---|
| Add particles | More molecules = more collisions |
| Increase temperature | Faster molecules = stronger collisions |
| Decrease volume | Same molecules in smaller space |
In a compressor, we mainly decrease volume to increase pressure.
Atmospheric Pressure
Atmospheric pressure varies with altitude:
| Location | Pressure |
|---|---|
| Sea level | 14.7 PSIA (1 atm) |
| Mexico City (~7,200 ft) | ~11.5 PSIA |
| La Paz, Bolivia (~11,800 ft) | ~9.5 PSIA |
Impact on compressors
At higher altitude, the compressor draws less dense air and produces less compressed air. A compressor in Mexico City produces ~20% less than at sea level.