Air Brake Systems Flashcards
7 cards from real CLP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Air Brake Systems flashcards as text
What is the purpose of the tractor protection valve?
Answer: To protect the tractor's air supply if the trailer develops a large air leak or breaks away
The tractor protection valve closes automatically if trailer air pressure drops too low, preserving the tractor's air supply so the tractor brakes continue to function.
What is the 'applied stroke' of a brake chamber, and why does it matter?
Answer: The distance the push rod travels when brakes are fully applied; must stay within legal limits to ensure effective braking
Applied stroke is how far the push rod extends when brakes are applied; excessive stroke reduces braking efficiency and indicates brakes need adjustment.
What does the yellow diamond-shaped control in the cab control?
Answer: The tractor parking and spring brakes
The yellow diamond-shaped control is the trailer air supply valve, which when pulled out shuts off air to the trailer and applies the trailer emergency brakes.
During a pre-trip inspection, what is the minimum air pressure you should have before driving a vehicle with air brakes?
Answer: 100 psi
You should not move the vehicle until air pressure is at least 100 psi, which ensures the safety systems have adequate pressure to function properly.
What is the proper way to check for air leaks in the brake system during a pre-trip inspection?
Answer: Build air to operating pressure, shut off engine, apply brakes, and watch pressure gauge for excessive drop
With engine off and pressure at operating level, apply and hold the foot brake for one minute and check that pressure does not drop more than 3 psi (single) or 4 psi (combination).
What causes 'compressor knock' or excessive compressor cycling, and what does it indicate?
Answer: A significant air leak in the system causing the compressor to work overtime to maintain pressure
If the compressor cycles on and off too frequently, it indicates a leak somewhere in the system that is causing pressure to drop faster than normal.
What is 'rollback' in the context of spring brakes, and how can it be prevented?
Answer: Backward vehicle movement when releasing the parking brake on a hill before applying the service brake; prevented by coordinating brake and throttle
Rollback occurs on hills when spring brakes are released before service brakes are applied or throttle is engaged, causing brief backward movement.