What happens if you leave the shut-off valves closed on the first trailer of a doubles combination?
a.Nothing, they should be closed
b.Air will not flow to the rear trailer brakes, causing them to not function properly
c.The front trailer brakes will fail
d.The tractor engine will stall
Explanation
If shut-off valves on the first trailer are left closed, air cannot flow to the second trailer, meaning the rear trailer brakes will not receive air pressure and may not function. This creates a dangerous situation with insufficient braking.