You asked: What color is the knob that controls the tractor protection valve?

The trailer air supply control on newer vehicles is a red 8-sided knob used to control the tractor protection valve. Push it in to supply the trailer with air, and pull it out to shut the air off and put on the trailer emergency brakes.

What are the red and yellow knobs in semi?

Re: Can anyone explain… Parking Brake & Trailer Air Supply

On a tractor, this is on either one or both drive axles. The steering has no parking brake. Pressing the yellow knob supplies air to one side these brake chambers, releasing the brakes.

What is another name for the tractor protection valve?

Any truck designed to pull a trailer with air brakes is going to be equipped with tractor protection system, which consists of the tractor protection valve–just to confuse you [CHCUCKLING] the system and the valve are called the same thing – the tractor protection valve and the red, eight-sided trailer air supply …

Where is the tractor protection valve located?

A tractor protection valve (Fig. 38) is usually mounted on the cab or chassis of the tractor. When the trailer-supply valve is open, air passes through the bottom of the tractor protection valve and charges the trailer through the supply line (also called the emergency line).

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What is the service line on a semi?

Quote From The CDL Manual:

The service line (also called the “control line” or “signal line”) carries air controlled by the foot brake or the trailer hand brake. Depending on how hard you press the foot brake or hand valve, the pressure in the service line will similarly change.

What is a hand valve?

The trailer hand valve, also called the trolley valve or Johnson bar, is used to work the trailer brakes. It should be used only to test the brakes. Using it while a vehicle is in motion could cause a skid.

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 is the main purpose of the tractor protection valve?

Application: Tractor protection valves are commonly mounted at the rear of the cab. The purpose of the Tractor Protection valve is to protect the tractor air brake system in the event of a trailer breakaway or severe air leak. They are also used to shut off air to the trailer before disconnecting the lines.

When the emergency line loses pressure what happens to the tractor protection valve?

When the emergency line loses pressure, it also causes the tractor protection valve to close (the air supply knob will pop out). Emergency lines are often coded with the color red (red hose, red couplers, or other parts) to keep from getting them mixed up with the blue service line.

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At what PSI do air brakes lock up?

If the pressure in the air system pulls below 60 psi, the parking brake knob will pop out and set the parking brakes. This is a safety feature so the truck will stop, because if the pressure falls too low, the service brakes will not work. The other system component stops the vehicle when you push on the brake pedal.

When backing under a tractor under a trailer you should expect?

Before backing the tractor under the trailer, adjust the landing gear to position the trailer at the proper height. The trailer should be just low enough that it will be raised slightly by the tractor when the tractor backs under it.

What does a trailer control valve do?

What do Trailer Control Valves provide? Trailer control valves optimize braking of tractor/trailer combinations by translating hydraulic input signals from tractors into pneumatic output signals to the trailer braking system.