If the driver accidentally uses the hand brake without the trailer connected, would there be an air loss?
- Only if the engine is off
- Only if the engine is on
- Yes
- No ✓
Answer: D. No
No. Using the hand valve with no trailer connected should not cause an air loss.
Why this is the answer
The handbook explains that when no trailer is connected, the trailer air supply valve stays closed. That lets the tractor be driven bobtail without air escaping from the disconnected glad hand couplers. The hand valve is described as a way to apply only the trailer brakes, such as when coupling. With no trailer hooked up, there is no trailer brake circuit connected to the tractor through those couplers, so the hand valve does not create an air loss there.
Why the other answers are wrong
- A. Only if the engine is off — The engine being off is not the condition that prevents air loss; the closed trailer air supply valve with no trailer connected is what the handbook describes.
- B. Only if the engine is on — The engine being on is not the reason air is kept from escaping; the handbook ties that protection to the trailer air supply valve being closed when no trailer is connected.
- C. Yes — This contradicts the handbook, which says no air is lost through the disconnected glad hand couplers when no trailer is connected.
Remember it
Think of the closed trailer air supply valve as the gate that keeps tractor air from spilling out of the disconnected couplers when there is no trailer.