A more detailed look at the air braking system, in particular with this video at the quick release valve.
QRV's are fitted to an air braking system to speed up the release of air, as it takes longer for air to escape a system than it does to put it in there. The main applications for quick release valves are in the service line to speed up the release of the service brakes, and in the secondary circuit to speed up the application of the park/secondary brakes. With a similar purpose to the air brake relay, the QRV is just there to speed up the release of compressed air from the braking system.

For a bit more background before watching this video, take a look at our "introduction to air brakes"    • Air Brakes - An Introduction. How it ...  

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