Inspection and Maintenance Tips
Every commercial motor vehicle equipped with an air brake system and used to tow a trailer with air brakes must be equipped with a tractor or towing-vehicle protection system.
Valves should be tested during drivers’ pre- and post-trip inspections and regularly maintained to ensure they function properly. During their inspections, drivers should check the valves for any signs of damage, corrosion or leaks, paying close attention to the connections and fittings. They can check for proper operation by conducting a few of the following tests:
System Leak Check: Overall system checks to ensure that there are no major air leaks at any valves or connections.
During this test, the driver will be monitoring the air pressure gauge and listening for audible air leaks. While hooked to the trailer with both the red and blue air lines connected, perform the following:
- Ensure that the wheel chocks are in place.
- Ensure that the air system is fully charged to at least 120 psi.
- With key on and engine off, press in the yellow tractor parking brake valve.
- Press in the red trailer parking brake valve and listen for audible leaks.
- Press and hold the foot valve (brake pedal) while watching the air pressure gauges. Once the air pressure stabilizes on the gauges, hold the brake pedal for one minute watching for any pressure loss. The maximum pressure loss allowed is 3 psi in one minute.
MV-3 and Tractor Protection Valve Check: The MV-3 valve controls airflow to the parking brakes on the tractor and trailer. The tractor protection valve controls the air supply to the trailer brakes.
During this test, the driver will simulate a major loss of air in the trailer to test the tractor protection valve operation.
- Ensure that the wheel chocks are in place.
- Ensure that the air system is fully charged to at least 120 psi.
- Leave the red (emergency) air line connected to the trailer.
- Ensure that the blue (service) trailer air hose is unhooked from the trailer and secured to prevent damage or injury during this test.
- It is suggested that they be secured to the deck plate with a bungee cord or similar device not be hooked to the dummy holders.
- With key on and engine off, press in both the yellow tractor parking brake valve and the red trailer valve.
- Next press foot valve (brake pedal).
- Air will escape from the blue air hose.
- Let the air escape until the red valve pops out on its own.
- Take foot off of foot valve (brake pedal).
- Note the pressure reading on the air gauges.
- It may pop out right away, which is OK.
- It needs to pop out on its own by the time it reaches 20 psi.
- If the valve fails to pop out on its own or the gauge is under 20 psi when it does, the MV-3 valve is defective.
- After the valve pops out, remove the red air line to ensure that air flow was stopped to the trailer emergency (parking brake) side of the system.
Trailer Hand Valve: The trailer hand valve controls airflow from the tractor to the trailer’s service air brake system without applying the tractor brakes.
This test is best performed while hooked to a trailer.
- Ensure that the wheel chocks are in place.
- Ensure that the air system is fully charged to at least 120 psi.
- With engine off, ensure both the yellow and red valves are in the out (brakes engaged) position.
- Disconnect and secure the blue (service) air line from the trailer.
- Leave the red (emergency) line connected to the trailer.
- Press in the red valve to release the trailer brakes.
- Pull the hand valve to apply the service brakes. You should hear air flowing through the blue (service) air line at this time.
- Release the hand valve and pull the red knob to set the trailer parking brakes.
- Pull the hand valve to apply the service brakes. Air should not be heard coming from the blue (service) line.
- If air is coming from the blue line at this time, the tractor protection valve is defective.
- Release the hand valve.
Anti-Bleed Back Valve (Check Valve): The anti-bleed back valve prevents air from bleeding back into the tractor’s brake system from the trailer. It ensures that the tractor’s brakes remain unaffected by any leaks or issues in the trailer’s brake system.
This test is performed while hooked to a trailer.
- Ensure that the wheel chocks are in place.
- Ensure that both air lines are connected to the trailer.
- Start the truck so that the unit can build air pressure.
- Press in the red (emergency) valve to fill the trailer air system.
- Watch the pressure gauges while the unit completely fills with air.
- When the air dryer pops off, check the pressure gauges the reading should be between 120 and 135 psi.
- Pull the red valve to set the trailer brakes.
- Shut the engine off.
- Remove both air lines from the trailer and listen/feel for any air coming out of the trailer gladhands.
- No air should be coming from the trailer.
- If air is escaping, a check valve in the system is defective.
As part of regular maintenance, technicians perform these same checks to ensure proper operation. Technicians also lubricate moving parts to ensure smooth operation and replace any worn or damaged components to maintain the system’s integrity.
Know What To Inspect
During the inspection of tractor protection system components, the inspector will:
- Ensure the wheel chocks are still in place and have the driver release all the brakes by pressing dash valves.
- Have the driver carefully remove the gladhands and allow air to escape.
- Ensure the air stops leaking from the supply line with at least 20 psi remaining.
- Listen and/or feel for any leaking air at the gladhand couplers on the trailer.
- Request a full-service brake application by the driver.
- Listen and/or feel for leaks from both air lines.
CVSA said air escaping from either the supply/emergency or service/control gladhand line of any vehicle equipped to tow an air-brake-equipped trailer indicates the unit has a defective tractor protection system and the vehicle is in an out-of-service condition.
CVSA created an inspection bulletin outlining tractor protection system testing procedures. It is available at www.cvsa.org/inspections/inspection-bulletins.
Roadcheck Inspectors To Complete Hundreds of Level I Inspections
Over the three days of International Roadcheck, inspectors conduct their North American Standard Level I Inspection, a thorough, 37-step procedure that examines vehicle components and driver documentation and requirements.
During the vehicle portion of a Level I Inspection, inspectors ensure the vehicle’s brake systems, cargo securement, coupling devices, driveline/driveshaft components, driver’s seat, fuel and exhaust systems, frames, lighting devices, steering mechanisms, suspension system, tires, wheels, rims, hubs and windshield wipers comply with regulations.
A vehicle that successfully passes a Level I or V Inspection without any critical vehicle inspection item violations may receive a CVSA decal, which is valid for three months. If out-of-service violations are found during an inspection, the vehicle will be restricted from operating until all out-of-service violations have been addressed.
Each year, the International Roadcheck emphasizes one aspect of potential violations. This year's emphasis is on tire safety. Inspectors will look for tire tread depth, tire pressure and proper clearance between tires, and examine the overall condition of the tires for things like cuts and bulges. While checking the tires of a vehicle is always a part of roadside inspections, CVSA is highlighting tire safety as a reminder to all drivers and carries of just how important it is.