How can you tell how much air pressure is in the service reservoirs?
- (a) Check the application pressure gauge on the dashboard.
- (b) Check the reservoir pressure gauges on the dashboard. ✓
- (c) Check the reservoirs manually with a portable pressure gauge.
- Do (a) or (c).
Answer: B. (b) Check the reservoir pressure gauges on the dashboard.
You read the reservoir pressure gauges on the dashboard to see how much air pressure is in the service reservoirs.
Why this is the answer
The handbook says air-brake vehicles have at least one air pressure gauge on the instrument panel that indicates pressure in the service reservoir system. It may be a single-needle gauge or a two-needle gauge showing primary and secondary reservoir pressure. Because it is mounted in the dashboard, you can watch reservoir pressure while driving and during a pre-trip inspection. A separate application gauge, where present, tells you how much air is being applied when the foot valve is depressed, not how much is stored in the reservoirs.
Why the other answers are wrong
- A. (a) Check the application pressure gauge on the dashboard. — The application pressure gauge, if the vehicle has one, shows how much air is being applied when the foot valve is pressed; it does not show stored reservoir pressure.
- C. (c) Check the reservoirs manually with a portable pressure gauge. — The passages describe dashboard reservoir gauges, not checking the reservoirs with a portable pressure gauge.
- D. Do (a) or (c). — Combining the application gauge with a manual portable check still misses the dashboard reservoir gauge that the handbook identifies for reading service reservoir pressure.
Remember it
Think stored versus applied: the reservoir gauge tells you what is stored, while the application gauge tells you what you are sending to the brakes.