What is the trailer hand valve (hand control) used for?

• A.To park the combination for long periods instead of the parking brake
• B.To steer the trailer around tight corners
• C.To test the trailer brakes, for example during coupling and inspection, by applying the trailer brakes independently
• D.To charge the trailer tanks while driving

Why

Applying trailer brakes alone with the hand control confirms they respond before the vehicle is moved. It is a testing tool, not a parking brake or a device for routine driving control.

Manual topic: Air Brakes - Trailer Air Brakes · From the Air Brakes practice bank (AB-238).

Practice this subject as a full test

More Tractor Protection Valve, Trailer Brakes & Stab Braking questions

• A trailer breaks away from the tractor and tears both air lines loose. What happens on the tractor side in the first moments?
• What does the trailer air supply control (the red control in the cab) do in normal operation?
• At about what pressure will the trailer air supply control pop out (or the tractor protection valve close) as system pressure falls?
• How do you test the tractor protection valve during an inspection?
• What is the difference between the trailer's emergency (supply) air line and its service air line?