CDL Air Brakes flashcards
CDL Air Brakes · 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.
- Air compressor
- Engine-driven pump that builds and maintains air pressure in the storage tanks. It is cooled and lubricated by the engine and runs whenever the governor calls for air.
- Governor
- Valve that controls the compressor by cutting it out at about 125 psi and cutting it back in at about 100 psi, keeping system pressure within a safe range.
- Safety valve
- Pressure-relief valve mounted on an air tank that releases air at about 150 psi, protecting the system if the governor fails and pressure keeps rising.
- Air storage tanks
- Tanks that hold compressed air for braking. Each has a drain valve at the bottom used to remove accumulated water and oil from the system.
- Alcohol evaporator
- Device that puts alcohol vapor into the air system so that moisture in the lines and valves will not freeze and block air flow in cold weather.
- Slack adjuster
- Lever linking the brake chamber pushrod to the brake shoe. It transfers and multiplies braking force, and its free play reveals whether adjustment is correct.
- Dual air brake system
- Two separate air circuits, primary and secondary, each with its own reservoir and check valves. If one circuit fails, the other still provides braking.
- Primary circuit
- The circuit in a dual air brake system that operates the rear brakes. It has its own reservoir and is protected by check valves from the other circuit.
- Secondary circuit
- The circuit in a dual air brake system that operates the front brakes, providing backup braking if the primary circuit loses its air pressure.
- Check valve
- One-way valve that lets air flow in a single direction only, preventing backflow and stopping air from escaping through a failed circuit or compressor.
- Tractor protection valve
- Valve that closes automatically when trailer air lines separate or the trailer is uncoupled, trapping air in the tractor so the driver can still stop.
- Static air leak check
- With the system fully charged and the engine off, air loss should not exceed 2 psi per minute for a single vehicle or 3 psi per minute for a combination.
- Applied air leak check
- With the brake pedal held down and the system charged, leakage should not exceed 3 psi per minute on a single vehicle or 4 psi per minute on a combination.
- Compressor build-up check
- At fast idle with a charged system, pressure should climb from 85 psi to 100 psi in 45 seconds or less, showing the compressor works properly.
- Low air pressure warning
- A light and buzzer that must activate before system pressure drops below 60 psi, warning the driver that spring brakes will soon apply automatically.
- Slack adjuster free play
- With the parking brake released, pull each slack adjuster by hand. Movement of more than about one inch indicates the brake is out of adjustment.
- Air tank draining
- Daily procedure of opening the drain valve at the bottom of each air tank to remove water and oil; only air and slight moisture should come out.
- Controlled braking
- Applying the brakes as hard as possible without locking the wheels while holding the steering wheel straight, then keeping pressure until the vehicle stops.
- Stab braking
- Technique for vehicles without ABS: apply the brakes fully, release the moment the wheels lock, and reapply. Never use stab braking on a vehicle with ABS.
- Brake fade
- Loss of braking power caused by heat from continuous or repeated brake use, which makes the pedal feel hard and stops the vehicle more slowly.
- Snub braking
- Downgrade technique of braking firmly to cut speed by about 5 to 10 mph, then releasing, and repeating instead of riding the brakes continuously.
- ABS braking technique
- Hold steady, firm pressure on the pedal and do not pump it. ABS prevents wheel lockup so you can steer while braking hard.
- Spring brake application range
- Spring brakes begin to apply automatically when system air pressure falls into the 20 to 45 psi range, and they stop the vehicle as pressure drops further.
- ABS malfunction lamp
- A yellow lamp that stays on to show the anti-lock system is not working. Normal service brakes still operate, but the wheels may lock under hard braking.
- Trailer breakaway braking
- If the trailer separates from the tractor, the emergency line loses pressure and the trailer spring brakes apply automatically to stop the trailer.
- Total air pressure loss
- When pressure is completely lost the spring brakes apply and the vehicle stops. It cannot be moved again until air pressure is restored.
- Modulating control valve
- A dash control that lets the driver apply the spring brakes gradually instead of all at once, useful for a controlled emergency stop.
- Parking brake on hill
- Set the parking brake, turn the front wheels toward the curb when facing downhill, and use wheel chocks so the vehicle cannot roll.
- Downgrade gear selection
- Shift into a low gear before the grade begins and stay in it all the way down, using the brakes only to control the vehicle's speed.
- Wet brake recovery
- After driving through deep water, drive slowly and apply light, steady brake pressure to heat and dry the linings until braking returns to normal.
- Escape ramp
- A gravel or sand-filled ramp built on a downgrade to stop a vehicle whose brakes have failed. Keep the vehicle straight and enter at speed.
- Stopping on slippery roads
- Release the brakes if the wheels lock, and use light, gentle applications plus engine braking to slow down without losing steering control.