Final answer:
Large vehicles with air brakes typically have spring brakes that are part of both the parking and emergency brake systems, ensuring safety even if air pressure is lost.
Step-by-step explanation:
Most large vehicles with air brakes have spring brakes which are part of both the parking and emergency brake systems. When air pressure in the brake system drops below a certain point, the spring brakes activate, acting as a fail-safe mechanism. This is crucial in air brake systems because it ensures the vehicle can be halted even if there's a loss of air pressure.
Commonly in large vehicles such as trucks and buses, air brakes utilize Pascal's principle, just like hydraulic systems. The air brake system must have the air properly bled out to prevent inefficiency due to the compressibility of gases. If air is not bled out of hydraulic brakes, for instance, a soft or spongy brake pedal could be the result, leading to reduced braking efficiency.