Upon trailer takeoff, air flows out of the supply line until the trailer supply valve closes automatically (automatic type). This prevents loss of air from the tractor.
What does a tractor protection valve do?
Application: The tractor protection valve is usually mounted at the rear of the cab. The purpose of the tractor protection valve is to protect the tractor’s air brake system in the event of a trailer breakaway or serious air leak. It is also used to shut off air to the trailer prior to disconnecting the line.
When should the tractor protection valve pop out?
6.2. When air pressure drops to the 20-45 psi range, the valve pops out (thus closing the tractor protection valve). Tractor protection valve controls or “emergency” valves on older vehicles may not automatically activate.
How do you test the tractor protection valve PSI?
Description The tractor protection valve should be tested by ensuring proper air supply, stopping the engine, and then depressing the brake pedal several times to release air from the system. If psi drops to a dangerous level, the tractor protection valve should move to the emergency position.
What PSI should a tractor protection valve be set at?
Testing the Tractor Protection Valve If the system air pressure is between 20 psi (138 kPa) and 45 psi (310 kPa), the trailer air supply valve will automatically open, shutting off air to the trailer.
At what pressure must the tractor protection valve operate to pass inspection?
As stated earlier, the tractor protection system is tested during roadside inspections and compliance is required. If the valve does not close prior to 20 psi, it is a prohibited use violation.”
What is the Blue Knob for in a semi?
Yellow is for brakes on all axles, red is for trailers only, and blue is for bogies only. It actually helps to have that blue one because in the winter you need to release the trailer brakes to keep residual water from freezing in the air lines.
At what PSI do air brakes lock up?
If the pressure in the air system drops below 60 psi, the parking brake knob pops out and the parking brake is applied. This is a safety feature that stops the truck because the service brakes will not function if the pressure drops too low. The other system component stops the vehicle when the brake pedal is depressed.
What is the red air line on a tractor trailer?
The red line is the trailer emergency brake air line. The green line is the electrical line. The blue line is the trailer service brake air line. Before moving the trailer, connect these lines to the corresponding couplers and sockets on the trailer.
Where is the tractor protection control valve located?
The tractor protection valve (Figure 38) is usually mounted on the cab or chassis of the tractor. When the trailer supple 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).
What will happen if the air lines are crossed?
If the air line is crossed, supply air is sent to the service line instead of charging the trailer air tank. No air is available to release the trailer spring brakes (parking brakes). If the spring brakes do not release when the trailer air supply control is pushed, check the air line connections.
Which valves are the tractor protection system?
The tractor protection system consists of two valves. One is the trailer supply valve (TSV), a push/pull valve located on the instrument panel. The other is the Tractor Protection Valve (TPV), which is located on the frame or body of the towing vehicle. The TPV is also referred to as the “tow vehicle” protection valve.
What is maximum leakage rate?
What is the maximum leakage rate? Less than 4 psi per minute for a single vehicle and less than 8 psi per minute for a combination vehicle.
What is normal air brake pressure?
The normal pressure range for air brake systems is approximately 690 to 828 kPa (100 to 120 psi). Drivers should know the normal pressure range for the vehicle in which they operate and should report any unusual conditions.
What will happen if the emergency air line between the tractor and the trailer comes apart?
Emergency air lines can break or pull apart during operation. Loss of pressure will result in the following Tractor protection valves hold air in the tractor or truck brake system if the trailer breaks off or develops a bad leak.
How do you break when you drive a tractor trailer combination with ABS?
When driving a tractor-trailer combination with ABS, the brakes must be applied as usual. In other words: – use only the braking force necessary to safely stop and maintain control. – Apply the brakes the same way regardless of whether the tractor, trailer, or both have ABS.
How do you test an inversion valve?
Operation and Leakage Tests Install one test gauge on the common control and supply lines. Install the other gauge at the delivery port. Gradually apply pressure to the common supply and control lines. In ascending order, note which pressure exhaust occurs and compare with vehicle manual.
When checking the trailer emergency brake the tractor protection control valve should be placed in what position?
Close tractor protection valve. Inspect landing gear. Tractor must be positioned: use tractor frame under trailer.
What causes weak air brakes?
– Acquire or burn bearings. -compressor carbon deposits in cylinder head. – Safety valves from adjustment. – Air pressure in the air brake system above normal due to defective unloader mechanism or failure of the governor.
How does an emergency relay valve work?
The relay’s emergency valve has a one-way check valve that stops the reservoir air from returning to the supply. The driver could open the trailer supplement valve to direct air pressure from the main reservoir to the trailer via the tractor protection valve.
What happens if the air pressure gets too low in the air brake system?
If one air system pressure is very low, either the front or rear brakes will not fully engage. This means it will take longer to come to a stop. Safely stop the vehicle and fix the air brake system.
What does Cola stand for air brakes?
(Governor cut-in) Air compressor governor cut-in is not below 85-110 psi.
What color is the service line?
Description Air lines may be color coded to help drivers avoid mistakes when joining glad hands. Typically, blue is used for service lines and red for emergency lines.
What are the two air lines on a truck?
This system protects the tractor air supply in case the trailer loses air. Thus, a tractor protection valve is a valve with two lines (glad hand lines) located behind the truck, often with the lines visible perpendicular to that valve.
What PSI should a tractor protection valve be set at?
Testing the Tractor Protection Valve If the system air pressure is between 20 psi (138 kPa) and 45 psi (310 kPa), the trailer air supply valve will automatically open, shutting off air to the trailer.
How do you test the tractor protection valve?
Description The tractor protection valve should be tested by ensuring proper air supply, stopping the engine, and then depressing the brake pedal several times to release air from the system. If psi drops to a dangerous level, the tractor protection valve should move to the emergency position.
When the emergency line loses pressure what happens to the tractor protection valve?
When the emergency line is pressurized, the tractor protection valve closes (air supply knob pops out). Emergency lines are often coded red (red hoses, red couplers, or other components) and are not to be confused with the blue service lines.
What is a tractor protection valve CDL?
The tractor protection valve holds air in the tractor or truck brake system in case the trailer breaks off or develops a bad leak. The tractor protection valve is controlled by a “trailer air supply” control valve in the cab. The control valve allows the tractor protection valve to be opened and closed.
Why should you lock the tractor glad hands to each other when you are not towing a trailer?
Why do tractor glad hands need to be locked to each other (or dummy couplers) when the trailer is not being towed? A It keeps dirt and water away from the lines.
Do you have pushed in the trailer supply valve you should not move the tractor until the whole air system?
Do not move throughout the air system after the trailer supply valve is pushed in. When coupling a semi-trailer, the front trailer supports (dollies) … are airlines with combination vehicles or usually do not get them. Mixed.
What should slack adjusters be set at?
Locate the Slack Adjuster adjustment mechanism. Usually requires a 9/16 wrench. Tighten all the way. You should see the S-Cams move and the brake shoes tighten against the drum. Then loosen 1/2 turn and you should be good.
Why must air tanks be drained CDL?
Why do I have to drain the air tank? Water and compressor oil can get into the tank and freeze in cold weather and cause brake failure.
How long should it take for a semi to build air?
The buildup of air pressure from 85 psi to 100 psi should take no more than 45 seconds. During operation, observe the air pressure gauge during the buildup to ensure proper air system operation. Apply the brake, pull in a safe location, and perform a 2 minute / 5 psi leak test.
Which air tank drains first?
When draining the tank, the supply tank should always be drained first. If the supply tank is drained first, any accumulated moisture can be removed before further passage into the system.
Why do you need a tractor protection valve?
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. It is also used to shut off air to the trailer prior to disconnecting the line.
When backing a tractor under a trailer you should CDL?
CDL
| Question | Answer. |
|---|---|
| When assisting a tractor under a trailer it should be in ___________. | Always use the lowest reverse gear. |
| After the trailer is coupled to the tractor, the tractor protection control valve should be placed in what propulsion? | Normal position. |
Is it OK to back the tractor into the trailer at an angle?
Place the tractor directly in front of the trailer. (Do not slant back under the trailer as this may push the trailer sideways and break the landing gear.)
Which shut off valves should be open and which closed CDL?
Adapted from the CDL manual : You must make sure that all shutoff valves are open except for the shutoff valve at the rear of the last trailer.
What does inversion valve do?
This is used on some vehicles equipped with a dual air system. This device uses the force of the spring brakes to provide a means to stop the vehicle if the rear (primary) air system fails.
What is the purpose of the tractor spring brake valve?
The spring brake control valve is designed to respond when the pressure in the air brake system falls below a specific level (typically 414 kPa or 60 psi) by expelling the remaining air holding the spring brakes in the released position.