Question The trailer hand valve should be used: Answers Regularly to activate the trailer brakes in all driving conditions. Only to test the trailer brakes. Only in inclement weather when the trailer may skid. Only if the trailer is carrying a load. Explanation The trailer hand valve should be used only to test the trailer brakes. It should not be used while driving because it may cause the trailer to skid. Take a FREE Practice Test Now This questions appears in the following tests: Illinois Tank ,