FAQ: Trailer Air Brakes Only Work When Connected To Tractor?

When the tractor protection valve is opened it allows air to?

When the pressure in the supply line reaches 45 psi, the service line port of the tractor protection valve opens. This allows application air pressure to travel down the service line to the trailer when a brake application is made.

What is the blue air line on a tractor trailer?

Air and Electrical Lines The red line is the air line for the trailer’s emergency brake. The green line is the electrical line. The blue line is the air line for the trailer’s service brake. Connect these lines to the corresponding couplers and socket on the trailer before moving the trailer.

How can you test the airflow to all trailers?

Check That Air Flows to All Trailers. 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.

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What gear should the tractor engine be in after you have uncoupled?

15. You want to inspect the trailer support. You should place the tractor transmission in which gear after you have uncoupled the trailer? Neutral.

What is the emergency air line for?

Emergency air line: The emergency line (also called the supply line ) has two purposes: (1) To supply air to the trailer air tanks, and (2) to control the emergency brakes on combination vehicles. Loss of air pressure in the emergency line causes the trailer emergency brakes to come on.

What color is the tractor protection valve?

The TPV is also called a ‘towing vehicle’ protection valve. The TSV has a red colored, eight-sided knob and is controlled by the driver. The driver opens (pushes in) the TSV when a trailer is being towed and closes it (pulls out) when there is no trailer present.

When backing a tractor under a trailer you should?


Question Answer
When backing a tractor under a trailer you should ___________. Always use the lowest reverse gear.
After the trailer has been coupled to the tractor, the tractor protection control valve should be placed in what posistion? Normal position.


Where are the shut off valves on a tractor trailer?

Shut – off Valves These valves permit closing the air lines off when another trailer is not being towed. You must check that all shut – off valves are in the open position except the ones at the back of the last trailer, which must be closed.

What Colour is the service line on a tractor unit?

Apply the tractor unit parking brake, stop the engine and remove the keys. Connect the service airline (yellow) and electrical connections. Connect the emergency airline (red) and watch for any unexpected movement.

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What will happen if the air lines are crossed when you hook up to an old trailer?

a. What will happen if the air lines are crossed when you hook up to an old trailer? a. The hand valve will apply the tractor brakes instead of the trailer brakes. If the trailer has no spring brakes, you could drive away but you would not have trailer brakes.

What happens if Blue Air Line breaks?

If broken or disconnected, loss of pressure automatically allows the spring-loaded parking brakes to apply. Pressure would be released either by the driver operating the parking brakes or— if the trailer somehow becomes disconnected—the line will break and the parking brakes fail safe; they apply.

What 3 methods can you use to secure a second trailer before coupling?

What three methods can you use to secure a second trailer before coupling? Release dolly brake by opening the air tank petcock or if the dolly has spring brake, use the dolly parking brake control. Wheel the dolly into position by hand so it is in line with the kingpin.

What might happen if the trailer is too high?

What might happen if the trailer is too high when you try to couple? If the trailer is too low, the tractor may stike and damage the trailer nose; if the trailer is too high, it may not couple correctly. If there is space something is wrong and the trailer would come loose very easily.

Why must air tanks be drained?

Why must air tanks be drained? Water and compressor oil can get inside of the tank and can freeze in cold weather and cause brake failure. When the air pressure is removed the springs put on the brakes. A parking brake control in the cab allows the driver to let the air out of the brakes.

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