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Petrol Fuel Tank Venting System Essentials
Pressure Regulation During Refueling
- Prevents positive pressure buildup from displaced air
- Enables smooth fueling by maintaining atmospheric pressure
- Avoids fuel backflow/splatter (up to 3 psi in 50L tanks without venting)
Pressure Balance During Engine Operation
- Prevents vacuum formation as fuel is consumed
- Avoids tank deformation (plastic tanks can deform at 0.5 psi negative pressure)
- Ensures continuous fuel supply to prevent engine stalling
Thermal Expansion and Contraction
- Accommodates fuel volume changes (~1.2% per 10°C temperature rise)
- Prevents overfilling/leaks during expansion
- Eliminates vacuum risk during cooling
Design Note:
Vents must handle both liquid fuel and vapor phases during rapid temperature changes
Safety: Preventing Explosive Pressures
| Risk | Venting Solution |
|---|---|
| Flammable vapor accumulation | Vapor dispersion via venting |
| Pressure buildup in fires | Flame arrestors prevent external ignition |
| Static discharge hazards | Properly grounded vent systems |
Environmental Protection
- Modern EVAP Systems capture vapors in charcoal canisters
- Pressure-relief valves activate at 7-15 kPa (positive) or 1-5 kPa (vacuum)
- Reduces VOC emissions by up to 95% compared to open vents
Design Considerations
- Location: Away from heat sources and moving parts
- Filtration: Prevents contaminants from entering tank
- Anti-slosh: U-shaped traps prevent fuel loss while allowing airflow
Engineering Tip:
Vent sizing must account for maximum fuel flow rates during both refueling and consumption