What function does a quick release valve perform?
- It helps in faster application of the brake
- It lets the parking brake release quickly
- It permits air to gradually exit the brake chamber
- It enables the pressurized air to exhaust near the brake chambers ✓
Answer: D. It enables the pressurized air to exhaust near the brake chambers
A quick release valve lets pressurized air exhaust near the brake chambers, so the brakes release quickly and completely.
Why this is the answer
The handbook explains that when you take your foot off the foot valve, the air in the lines and chambers has to travel all the way back to the foot valve exhaust port, and that distance creates a lag before the brakes let go. A quick release valve mounted close to the brake chambers solves this: the small amount of air in the line between the foot valve and the valve vents at the foot valve, while the larger volume in the chambers vents right at the quick release valve. That is why you hear a bigger burst of air there.
Why the other answers are wrong
- A. It helps in faster application of the brake — The valve works on the release side, not the apply side; the handbook says that when the brakes are applied, air flows through it to the chambers in the normal way.
- B. It lets the parking brake release quickly — It is not a parking brake control; its job is to vent pressurized air close to the brake chambers so the brakes release quickly and fully, though the handbook notes such valves can be fitted in spring parking brake circuits too.
- C. It permits air to gradually exit the brake chamber — It does the opposite of a gradual bleed: it dumps the chamber air rapidly at its own exhaust port instead of letting it travel slowly back to the foot valve.
Remember it
Listen for the loud burst near the wheels, not at the pedal: the quick release valve dumps chamber air right beside the brake chambers.