Pumping by the air compressor should start at about 100 psi and stop at about 125 psi (check manufacturerʼs specifications). Check air compressor governor cut-in and cut-out pressures: Otherwise, you could lose your brakes while driving. Check for air leaks, and repair before driving the vehicle. After the initial pressure drop, if the air pressure falls more than 3 psi in 1 minute for single vehicles and more than 4 psi for combination vehicles, the air loss rate is too much. Then apply 90 psi or more with the brake pedal. The loss rate should be less than 2 psi in 1 minute for single vehicles and less than 3 psi in 1 minute for combination vehicles. With a fully-charged air system (typically 125 psi), turn off the engine, release the parking brake, and time the air pressure drop. Do not drive until you get the problem repaired. If air pressure does not build up fast enough, the pressure may drop too low during driving, requiring an emergency stop. In single air systems (pre-1975), typical requirements are pressure build-up from 50 to 90 psi within 3 minutes with the engine at an idle speed of 600-900 RPM. Check the manufacturerʼs specifications).
When the engine is at operating RPM, the pressure should build from 85 to 100 psi within 45 seconds in dual air systems (if the vehicle has larger than minimum air tanks, the buildup time can be longer and still be safe. This causes the spring brakes to come on. The “parking brake” knob should pop out when the air pressure falls to the manufacturerʼs specification, usually in a range between 20 and 45 psi. Step on and off the brake pedal to reduce the air tank pressure. Check that spring brakes come on automatically:Ĭhock the wheels, release the parking brakes when you have enough air pressure to do it and shut the engine off. Only limited braking can be done before the spring brakes come on. In dual systems the stopping distance will be increased. This could cause sudden emergency braking in a single circuit air system.
If the warning signal does not work, you could lose air pressure and not know it. The low air pressure warning signal must come on before the pressure drops to less than 60 psi in the air tank, or the tank with the lowest air pressure in dual air systems. Turn the electrical power on, and step on and off the brake pedal to reduce air tank pressure.
Shut the engine off when you have enough air pressure that the low-pressure warning signal is not on. You can find it here: High Road 2.0 5.3 Inspecting Air Brake Systems (continued) STEP 7: Final Air Brake Checkĭo the following checks instead of the hydraulic brake check described in Section 2: Step 7 - Check Brake System. New! High Road 2.0! We have a new version of this program.
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