Passenger Safety and Air Brakes Flashcards

What is the procedure for carrying out an air brake 'drain and fill' check?

Answer: Drain reservoir taps, allow system to fully depressure, then run the engine and time how long it takes for full pressure to build — excessive time indicates a compressor or leak problem

Draining the reservoirs and timing the pressure build-up tests compressor efficiency and checks for leaks. The system should reach operating pressure within a specified time (typically 2-3 minutes from cold). A slow build indicates faults.

What is a 'static leak test' on an air brake system?

Answer: Build pressure to maximum, switch off the engine, and check that pressure holds within a specified range for a defined period — a rapid drop indicates a leak

With the system at full pressure and the engine off, a static leak test checks pressure retention. With brakes released, pressure should not drop more than 0.1 bar per minute. A higher drop rate indicates a significant leak.

What is the legal requirement for emergency exit hammer positions on a bus?

Answer: Emergency hammers must be clearly visible, accessible without obstruction, and positioned at each emergency window or exit requiring glass breaking

Emergency hammers must be positioned near emergency exits requiring glass breaking, clearly marked, and accessible without obstruction. They must be checked as part of pre-service inspection.

What does it mean if an air-braked vehicle's air dryer unit fails?

Answer: Moisture builds up in the air system — risk of ice formation in cold weather blocking the brake valves and causing brake failure

The air dryer removes moisture from compressed air before it enters the reservoirs and valves. Without it, moisture accumulates and can freeze in cold weather, blocking valves and causing brake failure or erratic brake behaviour.

What is the purpose of ABS (Anti-lock Braking System) on a heavy vehicle?

Answer: ABS prevents wheel lock during emergency braking — maintaining steering control and reducing stopping distance on most surfaces

ABS prevents wheel lock during hard braking by modulating brake pressure electronically. On a heavy vehicle, wheel lock on one axle (especially a steering axle) can cause loss of steering control — ABS maintains directional stability.

What is the 'trailer brake' control on a truck tractor unit and when should it be used?

Answer: A separate hand control that applies only the trailer brakes — useful for preventing trailer swing on slippery surfaces or during controlled stops on a gradient

The trailer brake control (hand valve) applies only the trailer brakes independently of the tractor. It can help stabilise a trailer that is beginning to swing and is used for parking on gradients when coupled.