Checking Doubles and Triples Air Brakes — CDL Doubles Triples Practice Test

This CDL Doubles Triples Checking Doubles and Triples Air Brakes practice set has 14 practice questions based on the official exam materials, each with an instant explanation. You need 80% on the real CDL Doubles Triples knowledge test to pass.

Sample questions

Three questions from the Checking Doubles and Triples Air Brakes bank with the correct answer and an explanation. The practice quiz above draws 14 questions at random from the same bank.

1. When checking the air brakes on a double or triple trailer, how do the checks compare with those for any other combination vehicle?

   • Do all the normal combination-vehicle checks, plus the additional checks for the extra trailers — Correct answer
   • Skip the normal combination-vehicle checks and do only the trailer checks
   • The checks are entirely different from a single-trailer vehicle
   • No air-brake check is needed for the rear trailers

   Explanation: Check the brakes on a double or triple as you would those of any combination vehicle (Subsection 6.5.2), plus the additional checks for the extra trailers and connections. English term: combination vehicle (组合车辆 / vehiculo combinado).

   Handbook: Section 7: Doubles and Triples — Checking Air Brakes

2. Before the air-flow test on doubles and triples, how do you hold the vehicle and how long do you wait?

   • Set the tractor parking brake and/or chock the wheels, then wait for air pressure to reach normal — Correct answer
   • Leave the brakes released and begin testing immediately
   • Drain all the air out of the tanks first
   • Run the engine at full throttle while testing

   Explanation: Use the tractor parking brake and/or chock the wheels to hold the vehicle, then wait for the air pressure to reach normal before testing. English term: parking brake (驻车制动 / freno de estacionamiento).

   Handbook: Section 7: Doubles and Triples — Air-Flow Test

3. During the air-flow test, what supplies air to the emergency (supply) lines and what supplies air to the service line?

   • Push in the red trailer air supply knob for the emergency lines; use the trailer handbrake for the service line — Correct answer
   • Pull out the red knob for the emergency lines; press the foot brake for the service line
   • Use the trailer handbrake for both the emergency and the service lines
   • Shut the engine off to charge the emergency lines

   Explanation: Push in the red trailer air supply knob to supply air to the emergency (supply) lines, and use the trailer handbrake to provide air to the service line. English term: trailer air supply knob (挂车供气旋钮 / perilla de suministro de aire del remolque).

   Handbook: Section 7: Doubles and Triples — Air-Flow Test