MD CDL Air Brakes flashcards
MD 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.
- Governor cut-out pressure
- The pressure at which the governor unloads the compressor, typically between 100 and 125 psi, stopping further air compression.
- Safety valve setting
- A valve set to open at about 150 psi to release excess pressure and protect the air brake system from over-pressurization.
- Low air pressure warning
- A red light and audible buzzer that must activate before air pressure drops below 60 psi, warning of impending spring brake application.
- Spring brake application pressure
- Spring brakes apply automatically when air pressure drops to approximately 45 psi, providing emergency braking.
- Air compressor build-up test
- With the engine at fast idle, the compressor must build pressure from 85 to 100 psi within 45 seconds.
- Static leak test
- With the engine off and system charged, pressure loss must not exceed 3 psi per minute for a single vehicle or 4 psi for a combination.
- Applied leak test
- With the engine running and brakes fully applied, pressure loss must not exceed 3 psi per minute.
- Slack adjuster free play
- With brakes released, the slack adjuster should not move more than about 1 inch (25 mm) at the pushrod when pulled by hand.
- Wet tank
- The reservoir that receives air directly from the compressor and collects moisture and oil; it must be drained daily.
- Air dryer function
- Removes moisture and contaminants from compressed air before it enters the wet tank, preventing corrosion and freeze-ups.
- Foot valve
- The brake pedal valve that controls the amount of air pressure applied to the brake chambers, providing graduated braking.
- Relay valve
- A valve that uses a small control signal to open a larger air passage, speeding up application and release of trailer brakes.
- Quick release valve
- A valve that speeds up the release of air from brake chambers when the pedal is released, reducing lag time.
- Brake chamber
- Converts air pressure into mechanical force via a diaphragm and pushrod to apply the foundation brakes.
- Slack adjuster
- Converts the linear pushrod stroke from the brake chamber into rotary motion to apply the foundation brake, providing mechanical advantage.
- Tractor protection valve
- Closes automatically when pressure drops to about 45 psi, preventing air loss from the tractor and applying the trailer brakes.
- Parking brake control
- The yellow diamond-shaped knob that applies the spring brakes when pulled out and releases them when pushed in, if air pressure is sufficient.
- Emergency stop with spring brakes
- Pull the parking brake knob gradually to apply spring brakes; sudden application can cause wheel lock and skidding.
- Brake fade
- Loss of braking effectiveness caused by overheating from continuous or excessive brake use, common on long downgrades.
- Stab braking
- A technique on long downgrades: apply brakes firmly, release when speed drops, and repeat to control speed without overheating.
- Lag time
- The delay between pedal movement and brake application, especially in long combination vehicles, requiring longer following distance.
- Graduated braking
- Pressing the brake pedal harder increases air pressure to the brake chambers, producing more braking force; releasing reduces pressure.
- Pumping the brake pedal
- Repeatedly pressing and releasing the pedal, which wastes air pressure and is not a normal braking technique.
- Spongy brake pedal
- A pedal that feels soft or goes to the floor indicates a leak or air in the system; the vehicle must be taken out of service.
- Daily air tank draining
- Draining the wet tank and dry tanks daily removes moisture and oil, preventing corrosion and freeze-ups in the air system.
- One-way check valve
- A valve that allows air to flow in one direction only, protecting the dry tank from pressure loss if the wet tank fails.
- Tug test
- With trailer brakes applied, gently pull the tractor forward to ensure the trailer is securely coupled and brakes hold.
- Pre-trip air brake inspection
- A check of compressor build-up, leak rates, warning devices, spring brakes, and slack adjusters before driving.
- Emergency relay valve
- A trailer valve that provides emergency braking if the trailer air supply is lost, applying the trailer spring brakes.
- Parking on a grade
- Apply parking brake, place transmission in low gear or park, and use wheel chocks if necessary to prevent rolling.
- Spring brake release pressure
- Spring brakes will not release unless air pressure is at least 45-60 psi; the vehicle cannot move until pressure builds.
- Cold weather air brake precaution
- Drain air tanks daily to prevent moisture from freezing in lines and valves; use alcohol evaporators if equipped.