Passenger Safety and Air Brakes Flashcards

What is the air pressure threshold at which the low-pressure warning alarm activates in an air brake system?

Answer: Typically around 4.5-5.5 bar — the alarm warns the driver before the pressure drops to spring brake activation level (around 2.5 bar)

The low-pressure warning alarm activates before pressure drops to the critical level where spring brakes apply automatically. This gives the driver time to pull over safely before losing control of the braking.

How does the air brake system maintain pressure during a long journey?

Answer: An engine-driven compressor continuously tops up the air reservoirs as air is used during braking

An air compressor driven by the engine continuously replenishes the air reservoirs. A governor valve stops the compressor when maximum pressure is reached and restarts it when pressure drops — maintaining consistent operating pressure.

What is the purpose of drainage taps on air brake reservoirs?

Answer: To drain water condensation that accumulates in the air system — water can freeze in cold weather and cause brake failure

Air compressors generate moisture from compressed atmospheric air. This moisture accumulates in reservoirs and can freeze in cold weather, blocking the air system and causing brake failure. Reservoirs must be drained regularly.

When a bus picks up wheelchair users, what specific safety procedures apply?

Answer: Wheelchair must be positioned and secured with approved anchoring systems — facing rearward or forward depending on vehicle specification — before moving off

Wheelchair users must be positioned in the designated wheelchair space and the wheelchair must be secured using all provided restraints (tie-down straps and anti-tip). The driver must confirm security before moving.

How does tyre pressure affect air-braked heavy vehicle braking performance?

Answer: Under-inflated tyres increase braking distance, reduce lateral stability, and increase the risk of overheating and blowout under heavy braking

Under-inflated tyres on a heavy vehicle create a larger contact patch but with reduced structural integrity. Under braking, the tyre can flex excessively, generating heat and increasing stopping distances. Overloaded under-inflated tyres are at high blowout risk.

What is 'brake proportioning' and why is it important in truck-trailer combinations?

Answer: Distributing braking force between tractor and trailer axles to prevent jackknifing — too much tractor braking relative to trailer braking causes jackknife

Brake proportioning ensures braking effort is shared correctly between tractor and trailer. If the tractor brakes harder than the trailer, the trailer pushes the tractor sideways — causing jackknife. EBS manages this electronically.