Air Brake Test System Components & Functions 2

Question 1

What is the function of the relay valve in a combination vehicle air brake system?

Accepted Answer

To speed up brake application and release at the trailer axles by responding to tractor brake line signals locally

Answer

To regulate air pressure supplied to the compressor

Answer

To connect the tractor and trailer air lines at the fifth wheel

Answer

To prevent air from flowing back into the supply tanks from the primary circuit

Question 2

What does the double check valve do in an air brake system?

Accepted 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

Answer

It allows air to flow in two directions simultaneously

Answer

It prevents pressure from exceeding the governor cut-out level

Answer

It equalizes pressure between the primary and secondary circuits

Question 3

What is the purpose of the foot valve (brake valve) in an air brake system?

Accepted Answer

To modulate and control the air pressure delivered to the service brakes in proportion to how hard the driver presses the pedal

Answer

To direct air to the spring brakes when the pedal is fully depressed

Answer

To release air from the wet tank directly to the brake chambers

Answer

To maintain constant pressure regardless of pedal position

Question 4

What does the spring brake modulating valve (also called the hand control valve or inversion valve) do?

Accepted Answer

It allows the driver to partially apply the spring brakes to control the vehicle if service brakes fail

Answer

It converts foot brake signals into hand brake applications automatically

Answer

It prevents spring brakes from applying when service brake air pressure is lost

Answer

It balances air pressure between front and rear axles during braking

Question 5

What is the function of the drain cock (manual drain valve) on an air tank?

Accepted Answer

To release accumulated water and oil from the tank to prevent corrosion and freezing

Answer

To manually adjust system operating pressure

Answer

To vent air when pressure exceeds governor cut-out

Answer

To connect the tank to the service brake circuit

Question 6

What is the difference between the primary and secondary air circuits in a dual air brake system?

Accepted Answer

The primary circuit typically operates the rear (drive) axle brakes and the secondary circuit operates the front axle and trailer brakes

Answer

The primary circuit is for service brakes and the secondary for spring brakes only

Answer

The secondary circuit supplies air only when the primary fails

Answer

There is no difference — both circuits supply the same brake groups