Ohio CDL Air Brakes Test flashcards
Ohio CDL Air Brakes Test · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Governor cut-out pressure
- The pressure at which the governor unloads the compressor, typically about 125 psi, stopping further air build-up in the system.
- Governor cut-in pressure
- The pressure at which the governor allows the compressor to reload, typically about 100 psi, beginning air build-up again.
- Safety valve function
- A spring-loaded valve on the supply tank that vents air at about 150 psi to prevent tank rupture if the governor fails to unload the compressor.
- Slack adjuster role
- Connects the brake chamber pushrod to the brake camshaft; it converts pushrod stroke into rotation of the S-cam to apply the brakes.
- Low-pressure warning threshold
- A buzzer and light must activate before system pressure falls below about 60 psi, warning the driver of insufficient air to stop safely.
- Dual air brake circuits
- Two separate circuits, primary and secondary, each with its own reservoir and check valve, so one failure still leaves braking capability.
- Primary circuit operation
- Typically operates the rear or drive axle brakes; it is one of the two independent circuits in a dual air brake system.
- Secondary circuit operation
- Typically operates the front or steering axle brakes; it provides braking if the primary circuit fails.
- Tractor protection valve
- A safety valve that closes automatically when tractor pressure drops below about 20-45 psi, preventing air loss and protecting tractor brakes.
- Trailer air supply valve
- The red push-pull button in the cab that controls the tractor protection valve to charge or release the trailer air lines.
- Static leak test limit
- With the engine off and system charged, pressure should not drop more than 3 psi per minute for a single vehicle or 4 psi for a combination.
- Compressor build-up test
- With the engine running, pressure should build from 85 to 100 psi within 45 seconds; slower build-up indicates a weak compressor or leak.
- TPV manual check
- With the system charged, close the TPV and open the trailer air supply valve; air must not escape from the tractor's trailer lines.
- Reservoir drain procedure
- Open the drain valve at the bottom of each tank daily to remove moisture and oil; the supply tank collects the most water.
- Applied leakage test
- With the engine off and brakes fully applied and held, pressure should not drop more than 3 psi per minute single or 4 psi combination.
- TPV automatic test
- Reduce tractor pressure while the trailer is charged; the TPV should close and the trailer spring brakes should apply automatically.
- Out-of-service criteria
- If leak rate, low-pressure warning, or TPV tests fail, the vehicle must be placed out of service until repairs are completed.
- Governor unload test
- Run the engine until the compressor unloads at about 125 psi, then verify it reloads at about 100 psi; continuous running indicates failure.
- Brake lag
- The delay of about 0.3 to 0.5 seconds between pressing the pedal and brake application in an air brake system, adding to stopping distance.
- Brake fade
- Loss of stopping power from overheated drums caused by repeated heavy braking; use engine braking and lower gears on downgrades to avoid it.
- Emergency stop technique
- Apply the brake pedal firmly and hold it; do not pump the brakes, which wastes air and reduces braking effectiveness.
- Following distance rule
- Allow at least one second per 10 feet of vehicle length, plus one second for speeds above 40 mph, to account for brake lag.
- Downgrade braking strategy
- Select a low gear before descending and use brakes intermittently rather than riding them, avoiding overheating and brake fade.
- Spring brake operation
- A heavy coil spring applies the brakes when air pressure is released; air pressure is required to release the spring and free the wheels.
- Parking brake control
- The yellow push-pull button releases air from the spring brake chambers to apply the brakes; pushing it in recharges the chambers to release.
- Automatic spring application
- If air pressure drops below about 20-45 psi, the spring brakes apply automatically as a fail-safe to stop the vehicle.
- Caging a spring brake
- Inserting and tightening the caging bolt to compress the spring manually, a temporary measure for towing or moving a disabled vehicle.
- ABS purpose
- Prevents wheel lock-up during braking by modulating air pressure to individual wheels, improving steering control and reducing stopping distance on slippery surfaces.
- ABS warning light
- The amber light should come on at ignition and go off after a few seconds; if it stays on, ABS is disabled but normal air brakes still work.
- Low-pressure while driving
- If the warning activates while driving, pull over safely, set the parking brake, and investigate; do not continue with low air pressure.
- Compressor failure symptom
- Pressure fails to build or drops continuously; the vehicle must not be driven until the compressor or governor is repaired.
- Trailer ABS check
- Inspect the trailer ABS light during the walk-around; a malfunction does not affect tractor brakes but should be reported and repaired.