Common Air Brake Valve Failures and How To Fix Them

Semitruck drivers face dangerous situations when air brake systems malfunction. Since the brakes depend on properly functioning valves, it’s important to know how to identify and address these issues. Learn the causes behind common air brake valve failures and how to fix them.

Stuck or Frozen Relay Valves

Relay valves control air flow between the primary and secondary brake circuits, amplifying the signal from the brake pedal to the brake chambers. Moisture contamination, dirt buildup, and worn internal seals cause the valves to stick. Symptoms include delayed brake response, uneven braking between axles, and complete brake failure on affected circuits.

How To Fix It

Disconnect the air supply lines and remove the relay valve from its mounting bracket. Disassemble the valve according to the manufacturer’s specifications, and inspect all internal components for wear, corrosion, or debris.

Clean all parts thoroughly with appropriate solvents and replace damaged seals, springs, or diaphragms. Reassemble the valve using proper torque specifications and test operation before reinstalling it on the vehicle.

Malfunctioning Quick-Release Valves

Quick-release valves speed up brake application and release cycles by providing a direct exhaust path for air chambers. When these valves fail, they typically stick in either the open or closed position. Stuck open valves cause slow brake release and drag, while stuck closed valves result in sluggish brake application and poor stopping performance.

How To Fix It

Remove the quick-release valve from the brake chamber and examine the internal spring and diaphragm assembly. Replace any damaged components and clean the valve body thoroughly to remove accumulated debris. Check the exhaust port for blockages and clear as needed. Install a new valve if internal damage appears extensive, as these components are relatively inexpensive compared to the consequences of complete brake failure.

Leaking Tractor Protection Valves

Tractor protection valves prevent air loss from the tractor’s brake system when the trailer becomes disconnected. Internal seal failure or spring damage causes these valves to leak continuously, reducing system pressure and compromising brake performance. Visible air leaks around the valve body or gladhand connections signal the need for immediate attention.

How To Fix It

Shut off the vehicle and drain the air system completely before beginning repairs. Inspect the valve seat, springs, and sealing surfaces for damage or excessive wear.

Replace all internal seals and gaskets, paying special attention to the main diaphragm that controls valve operation. Test the repaired valve for proper pop-out pressure before returning the vehicle to service.

Faulty Pressure Protection Valve Operation

The pressure protection valve maintains a minimum system pressure for steering and emergency brakes. When this valve malfunctions, it may allow pressure to drop below safe operating levels or prevent the system from building adequate pressure.

How To Fix It

Test the valve’s cut-in and cut-out pressures using calibrated gauges to verify proper operation. Remove and disassemble the valve if pressure settings fall outside the vehicle’s desired range.

Clean all internal components and replace worn springs, seals, or adjustment mechanisms. Recalibrate the valve, and verify correct operation through multiple pressure cycles.

Failing Inversion Valves

Inversion valves control the operation of spring brake chambers and can fail to release or apply spring brakes properly. When these valves malfunction, spring brakes may remain engaged during normal operation or fail to apply during emergency situations. Internal pilot valve problems typically cause these failures.

Contaminated air supply affects the sensitive pilot valve mechanism within the inversion valve. Worn or damaged seals allow air to leak internally. Temperature fluctuations can cause rubber components to harden and lose flexibility.

How To Fix It

Remove the inversion valve from the spring brake chamber and disassemble according to service manual procedures. Inspect the pilot valve assembly for proper seating and freedom of movement. Check all internal seals and O-rings for damage or deterioration.

Replace the pilot valve assembly if damaged, and install new seals throughout the valve body. Verify that all air passages remain clear and unobstructed. Reassemble the valve and install it in the spring brake chamber. Then, test the spring brake and release functions.

Defective Foot Brake Valves

Foot brake valves translate pedal input into proportional air pressure signals throughout the brake system. Common failures include internal seal leaks, stuck pistons, or damaged return springs. These problems manifest as a spongy pedal feel, inconsistent brake response, or air leaks audible during brake application.

How To Fix It

Begin diagnostics by checking for external air leaks around valve connections and the exhaust port. Remove the valve from the vehicle and disassemble carefully, noting the position of all internal components. Clean the valve body and inspect all seals, springs, and moving parts for damage. Discard any worn components, and reassemble the brakes by adhering to the vehicle’s spring preload and seal orientation specifications.

Inoperative Brake Application Valves

Brake application valves control air delivery to individual brake chambers and can fail due to contamination or component wear. Symptoms include

• Individual wheels failing to apply brakes.
• Uneven brake application across the axles.
• Air leaks when braking.
• Delayed brake response on affected wheels.

How To Fix It

Isolate the affected valve by testing brake application at each wheel position. Remove the malfunctioning valve and inspect for internal damage or contamination. Disassemble and clean all components, paying attention to small orifices that can become blocked.

Replace damaged seals, springs, or valve bodies as needed. Verify proper airflow and pressure delivery before completing the repair.

Damaged Air Brake Relay Emergency Valves

Emergency relay valves activate the spring brakes when air pressure drops below safe levels or when applying the parking brake. Valve damage prevents proper emergency brake function and creates dangerous driving conditions. These valves may fail to activate spring brakes during emergencies or may not release after restoring the air pressure.

How To Fix It

Test emergency valve operation by reducing system pressure while monitoring brake chamber response. Remove the valve assembly and inspect the emergency and service chambers separately. Clean all internal surfaces and replace worn diaphragms, seals, and springs.

Pay special attention to the balance spring that controls the emergency activation point. After reassembly, test the valve at various pressure levels to verify proper emergency and service brake operation.

Air Brake Valve Failures Require Expert Solutions

Professional diagnosis and repair of air brake valve problems requires specialized knowledge and quality replacement components. Van Horn Truck Parts offers an extensive selection of air brake valves to address these common failures, so you can fix any issues that arise. Our inventory includes relay valves, quick-release valves, protection valves, application valves, and complete emergency valve assemblies from trusted manufacturers.