What does the low air pressure warning device warn you about?
- The service tank system pressure has fallen too low. ✓
- There is too much moisture in the braking system.
- It will soon rain or snow.
- The governor cut-in pressure is set too low.
Answer: A. The service tank system pressure has fallen too low.
The low air pressure warning device warns you that the service tank system pressure has fallen too low.
Why this is the answer
The handbook says the low-air warning must come on when air pressure drops below about 60 p.s.i. When it activates, you should pull over and stop, then find out why the air pressure was lost before going further. That matches a warning about system air pressure falling too low, not a notice about moisture, weather, or a governor setting. The passages describe the warning in terms of air pressure in the system, so the service-tank wording in the answer fits that general rule, though the excerpts do not separately name the service tank.
Why the other answers are wrong
- B. There is too much moisture in the braking system. — The passages describe the warning as being about low air pressure, not about too much moisture in the braking system.
- C. It will soon rain or snow. — The warning is tied to air pressure dropping below the warning level, not to upcoming rain or snow.
- D. The governor cut-in pressure is set too low. — The passages say the warning comes on when actual air pressure drops below about 60 p.s.i.; they do not describe it as a warning that the governor cut-in pressure is set too low.
Remember it
Remember that the low-air warning is about air pressure itself: when it sounds or shows, stop and look for the air loss before you move.