eli5 Why do trucks and busses do the “tsshhh” thing when they stop?
In: Engineering
Most air systems work in reverse. The pressurized air keeps the brake off, the brake pedal releases an incremental amount of air to apply the brake. The whoosh is the park brake releasing the air to set the bake on firm. The pshh to release the park brake is the valve letting air back in the system to release the brake.
Edit: the idea is, if there was a total loss of the air system, the brakes would engage instead of no brakes.
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