CDL Practice Tests For Doubles And Triples Page 3

Never unlock the pintle hook with the dolly still under the rear trailer. The dolly tow bar may fly up, possibly causing injury and making it very difficult to re-couple.

Uncouple converter dolly:

• Lower dolly landing gear.
• Disconnect safety chains.
• Apply converter gear spring brakes or chock wheels.
• Release pintle hook on first semitrailer.
• Slowly pull clear of dolly.

Shut-off valves (at rear of trailers, in service and emergency lines)

• Rear of front trailers: OPEN
• Rear of last trailer: CLOSED
• Converter dolly air tank drain valve: CLOSED

Shut-off valves (at rear of trailers, in service and emergency lines)

• Rear of front trailers: OPEN
• Rear of last trailer: CLOSED
• Converter dolly air tank drain valve: CLOSED

Check air flow to all 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.

Test tractor protection valve:

Charge the trailer air brake system, (i.e., 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).

Test tractor protection valve:

Charge the trailer air brake system, (i.e., 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).

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 “emergency” position. Pull gently on the trailer with the tractor to check that the trailer emergency brakes are on.

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.)

If the tractor protection valve does not 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.