1. What two things are important to prevent rollover? 2. When you turn suddenly while pulling doubles, which trailer is most likely to turn over? 3. Why should you not use the trailer hand brake to straighten out a jackknifing trailer? 4. What is offtracking? 5. When you back a trailer, you should position your vehicle so you can back in a curved path to the driver’s side. True or False? 6. What type of trailers can get stuck on railroad-highway crossings?
2015-2016 Commercial Driver’s License HandbookSection 6 - Combination Vehicles Page 6-5 in the cab. The control valve allows you to open and shut the tractor protection valve. The tractor protection valve will close automatically if air pressure is low (in the range of 20 to 45 psi). When the tractor protection valve closes, it stops any air from going out of the tractor. It also lets the air out of the trailer emergency line. This causes the trailer emergency brakes to come on, with possible loss of control. (Emergency brakes are covered later.) 6.2.3 –Trailer Air Supply Control The trailer air supply control on newer vehicles is a red eight-sided knob, which you use to control the tractor protection valve. You push it in to supply the trailer with air, and pull it out to shut the air off and put on the trailer emergency brakes. The valve will pop out (thus closing the tractor protection valve) when the air pressure drops into the range of 20 to 45 psi. Tractor protection valve controls or "emergency" valves on older vehicles may not operate automatically. There may be a lever rather than a knob. The "normal" position is used for pulling a trailer. The "emergency" position is used to shut the air off and put on the trailer emergency brakes. 6.2.4 –Trailer Air Lines
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