Tractor protection valves are usually mounted at the rear of the cab. Their job 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.
What controls 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 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.
Where are shut off valves located CDL?
Quote From The CDL Manual:
Shut-off valves (also called “cut-out cocks”) are used in the service and supply air lines at the back of trailers used to tow other trailers.
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.
At what pressure must the tractor protection valve operate to pass inspection?
Between approximately 20-40 PSI on a tractor-trailer combination vehicle, the tractor protection valve and parking brake valve should close (pop out). On other combination vehicle types and single vehicle types, the parking brake valve should close (pop out).
What is the blue air brake button for?
The yellow one controls brakes on all axles, the red is only for trailer, and the blue is only for the truck unit.
When should you drain your air tanks?
Each air tank is equipped with a drain valve in the bottom. There are two types: Manually operated by turning a quarter turn or by pulling a cable. You must drain the tanks yourself at the end of each day of driving.
What color is the service line on a tractor trailer?
In most cases, the trailer couplers are colour-coded during manufacturing – red for the supply line and blue for the service line (See Diagram 5-2). By matching these colours, the lines are properly connected.
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 is the blue air line on a tractor trailer?
The blue line is the service brake line. This allows the trailer brakes to be applied when driving. The green line is the electrical connector.
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.
Which shutoff valve is open and closed?
All shut-off valves should be open. The valves at the back of the last trailer should remain closed. … Only the valves on the back of the first trailer should be closed.
What might happen if trailer is too high when you try to couple?
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. … Go under the trailer and look into the back of the fifth wheel.