Transcript
Commercial Driver License Study Group
2012
Section 7 Doubles and Triples
Driving safely
• Steer gently
• Drive slowly on curves, on/off ramps, corners
• Last trailer most likely to turn over
• More critical parts to inspect
Driving safely
• Look far ahead
• More space needed – front/back/sides
• More careful in adverse condition
• Park to pull straight through
• Converter dollies have anti-lock brakes
Coupling / uncoupling
• For safest handling on road, put heaviest trailer immediately behind tractor, then lighter trailer
• Converter gear on a dolly is a coupling device of 1 or 2 axles and a fifth wheel by which a semitrailer can be coupled to the rear of a tractor-trailer combination forming a double bottom rig.
Coupling / Uncoupling Twin Trailers
• Sequence on pages 7.1 to 7.2
Coupling / Uncoupling Triple Trailers
• Sequence page 7.2
Inspecting Doubles & Triples
• Coupling system areas
– Fifth wheel (lower)
– Fifth wheel (upper)
– Air and electric lines to trailer
– Sliding fifty wheel
Inspecting Doubles & Triples
• Landing gear
– Fully raised, no missing parts, not damaged
– Crank handle in place and secured
– If power operated, no air or hydraulic leaks
Inspecting Doubles & Triples
• Double & triple trailers
– Shuf-off valves
– Air lines supported and glad hands connected
– Spare tire secure
– Pintle-eye of dolly in place
– Pintle hook latched
– Safety chains secured to trailers
– Light cords are firmly in sockets on trailers
Air brake check
• Check as for any combination vehicle plus ---
• Air flows to all trailers
– Put on tractor parking brake
– When air pressure up, push in “trailer air supply” knob = supply air to emergency lines.
– Use trailer handbrake to put on trailer service brakes
Air brake check
• At back of last trailer
– Open emergency line shut-off valve = hear air
– Close it
– Open the service line valve = hear air
– Close it
– If you do NOT hear air escaping, check valves up the line – they should be OPEN.
Air brake check
• Test tractor protection valve
– Build up normal air pressure and push “air supply” knob in
– Shut engine off
– Step on/off brake pedal to reduce air pressure
– Tractor protection valve should pop out at 20 to 45 psi
– Failure to do so = emergency brakes come on
Air brake check
• Test trailer emergency brakes
– Charge trailer air brake system
– Trailer rolls freely
– Stop, pull out trailer air supply control
– Pull gently on trailer with tractor
Air brake check
• Test trailer service brakes
– Check for normal air pressure
– Release parking brakes
– Move vehicle forward slowly
– Apply trailer brakes (with hand control – trolley valve)
– Should feel brakes come on
– NOTE: tested with hand control, drive with foot pedal
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