Page 7-4 Section 7 – Doubles and Triples  2005 Model Commercial Driver’s License Manual 7.3.2 – Additional Things to Check During a  Walkaround Inspection  7.4 – Doubles/Triples Air Brake Check  7.4.1 – Additional Air Brake Checks  Section 7 Test Your Knowledge  Check That Air Flows to All Trailers (Double  and Triple Trailers). Use the tractor parking brake  and/or chock the wheels to hold the vehicle. Wait  for air pressure to reach normal, then push in the  red "trailer air supply" knob. This will supply air to  the emergency (supply) lines. Use the trailer  handbrake to provide air to the service line. Go to  the rear of the rig. Open the emergency line shut- off valve at the rear of the last trailer. You should  hear air escaping, showing the entire system is  charged. Close the emergency line valve. Open  the service line valve to check that service  pressure goes through all the trailers (this test  assumes that the trailer handbrake or the service  brake pedal is on), and then close the valve. If you  do NOT hear air escaping from both lines, check  that the shut-off valves on the trailer(s) and  dolly(ies) are in the OPEN position. You MUST  have air all the way to the back for all the brakes to  work.  Test Tractor Protection Valve. Charge the trailer  air brake system. (That is, build up normal air  pressure and push the "air supply" knob in.) Shut  the engine off. Step on and off the brake pedal  several times to reduce the air pressure in the  tanks. The trailer air supply control (also called the  tractor protection valve control) should pop out (or  go from "normal" to "emergency" position) when  the air pressure falls into the pressure range  specified by the manufacturer. (Usually within the  range of 20 to 45 psi.)  If the tractor protection valve doesn't work properly,  an air hose or trailer brake leak could drain all the  air from the tractor. This would cause the  emergency brakes to come on, with possible loss  of control.  Test Trailer Emergency Brakes. Charge the  trailer air brake system and check that the trailer  rolls freely. Then stop and pull out the trailer air  supply control (also called tractor protection valve  control or trailer emergency valve) or place it in the  These questions may be on your test. If you can’t  answer them all, re-read Section 7.  Test Trailer Service Brakes.  Check for normal air  pressure, release the parking brakes, move the  vehicle forward slowly, and apply trailer brakes  with the hand control (trolley valve), if so equipped.  You should feel the brakes come on. This tells you  the trailer brakes are connected and working. (The  trailer brakes should be tested with the hand valve,  but controlled in normal operation with the foot  pedal, which applies air to the service brakes at all  wheels.)  "emergency" position. Pull gently on the trailer with  the tractor to check that the trailer emergency  brakes are on.  Check the brakes on a double or triple trailer as  you would any combination vehicle. Subsection  6.5.2 explains how to check air brakes on  combination vehicles. You must also make the  following checks on your double or triple trailers  Do these checks in addition to subsection 5.3,  Inspecting Air Brake Systems.  10. How do you know if your converter dolly is  equipped with antilock brakes?  9.  How can you test that air flows to all trailers?  8.  Should the shut-off valves on the rear of the  last trailer be open or closed? On the first  trailer in a set of doubles? On the middle trailer  of a set of triples?  7.  What should you check for when inspecting  the converter dolly? The pintle hook?  6.  Why should you pull a dolly out from under a  trailer before you disconnect it from the trailer  in front?  5.  What do you check when making a visual  check of coupling?  4.  How do you check to make sure trailer height  is correct before coupling?  3.  What three methods can you use to secure a  second trailer before coupling?  2.  Do converter dollies have spring brakes?  1.  What is a converter dolly? 