What is the one-way check valve's primary role in the brake system?

To select air from either the foot valve or the hand valve
To prevent air from bleeding back from the service reservoir to the supply reservoir ✓
To prevent air from bleeding back from the supply reservoir to the service reservoir
To select air from either the primary service reservoir or the secondary service reservoir

Answer: B. To prevent air from bleeding back from the service reservoir to the supply reservoir

The one-way check valve keeps air from bleeding back from the service reservoir to the supply reservoir.

Why this is the answer

The handbook describes the one-way check valve as a valve that lets air move in a single direction only. Air travels from the supply reservoir into the primary and secondary service reservoirs, and the valve closes off the return path. The reason given is that the air already stored in the service reservoirs must not flow backward and be lost if the compressor, the compressor discharge line, or the supply reservoir fails. So the valve protects the stored braking air in the service reservoirs rather than controlling which valve applies the brakes.

Why the other answers are wrong

A. To select air from either the foot valve or the hand valve — Choosing between air from the foot valve or the hand valve is the job of a two-way check valve, not the one-way check valve described in the handbook.
C. To prevent air from bleeding back from the supply reservoir to the service reservoir — This reverses the flow: the handbook says air normally moves from the supply reservoir into the service reservoirs, and the valve stops it from going back, not the other way around.
D. To select air from either the primary service reservoir or the secondary service reservoir — Selecting air from the primary or secondary service reservoir is again two-way check valve work, and the passage ties the one-way valve to filling the service reservoirs from the supply reservoir.

Remember it

Picture the valve as a turnstile: air walks in from the supply reservoir to fill the service reservoirs, but the gate won't let it walk back out.

Official handbook: ICBC Driving Commercial Vehicles, 8 Air brakes – Components of a dual air brake system, p. 156

Explanation drafted with AI (deepseek-flash) from the official handbook passage cited above, then checked automatically and by a second model on 2026-10-23. Always confirm with the official handbook.

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