System Components & Functions Flashcards
6 cards from real Air Brake Test practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 System Components & Functions flashcards as text
What is the function of the relay valve in a combination vehicle air brake system?
Answer: To speed up brake application and release at the trailer axles by responding to tractor brake line signals locally
Relay valves are located near the trailer axles and apply/release trailer brakes using local air supply rather than waiting for air to travel the full distance from the tractor, reducing brake lag.
What does the double check valve do in an air brake system?
Answer: It allows the highest of two incoming air pressures to pass through to operate a common component, such as stopping lights or spring brake release
Double check valves select the higher of two input pressures to supply a single output, commonly used so either the service brake application or the parking brake circuit can trigger the brake lights.
What is the purpose of the foot valve (brake valve) in an air brake system?
Answer: To modulate and control the air pressure delivered to the service brakes in proportion to how hard the driver presses the pedal
The foot valve is a graduated control device that delivers more or less air to the service brakes depending on the force applied to the pedal, allowing the driver to modulate braking.
What does the spring brake modulating valve (also called the hand control valve or inversion valve) do?
Answer: It allows the driver to partially apply the spring brakes to control the vehicle if service brakes fail
The spring brake modulating valve allows manual, graduated control of spring brake application, useful as a modulated emergency brake if the service brake system fails.
What is the function of the drain cock (manual drain valve) on an air tank?
Answer: To release accumulated water and oil from the tank to prevent corrosion and freezing
The drain cock is opened to expel water and oil that accumulate at the bottom of air tanks, preventing corrosion inside the tank and ice formation in cold weather.
What is the difference between the primary and secondary air circuits in a dual air brake system?
Answer: The primary circuit typically operates the rear (drive) axle brakes and the secondary circuit operates the front axle and trailer brakes
In a typical dual air system, the primary circuit serves the rear axles and the secondary circuit serves the front axle; if one fails, the remaining circuit can still provide braking on those axles.