CLP Air Brake Systems 5

Question 1

What is a 'modulating control valve' and in what situation would a driver use it?

Accepted Answer

A hand-operated valve that lets a driver gradually apply spring brakes when service brakes fail

Answer

A valve used to gradually apply trailer brakes when descending steep grades

Answer

An automatic valve that modulates ABS brake pressure at each wheel

Answer

A pressure regulator that keeps air pressure from exceeding safe limits

Question 2

What effect does cold weather have on air brake systems, and how should drivers prepare?

Accepted Answer

Moisture in the system can freeze, blocking valves and lines — drivers should drain tanks and use alcohol evaporators or air dryers

Answer

Cold air is denser, increasing pressure — drivers should reduce pressure by 10 psi in winter

Answer

Cold weather reduces compressor output — drivers need more warm-up time before driving

Answer

Brake drums contract in cold weather, making adjustment unnecessary until temperatures rise

Question 3

What is the correct maximum push rod stroke for a Type 30 brake chamber before adjustment is required?

Accepted Answer

2.0 inches

Answer

1.5 inches

Answer

2.5 inches

Answer

3.0 inches

Question 4

What does it mean when the brake pedal feels 'spongy' or requires more travel than usual on an air brake vehicle?

Accepted Answer

Brakes are out of adjustment or there is a problem such as air in the hydraulic portion of a system

Answer

The air dryer filter is clogged and needs replacement

Answer

Air pressure is too high — the governor needs to be reset

Answer

The brake lining has glazed from overheating and needs a cool-down period

Question 5

How do antilock braking systems (ABS) affect air brake operation on commercial vehicles?

Accepted Answer

ABS monitors wheel speed and modulates air pressure to prevent wheel lockup while keeping maximum braking force

Answer

ABS replaces the need for air brakes by using electronic actuators to stop the vehicle

Answer

ABS reduces maximum air pressure to 80 psi to prevent skids on wet roads

Answer

ABS allows the driver to steer while skidding by automatically applying opposite brakes

Question 6

When inspecting air brake hoses and lines during a pre-trip inspection, what conditions should cause you to take the vehicle out of service?

Accepted Answer

Hoses that are cracked, chafed, worn through, crimped, or leaking air

Answer

Hoses that have any color other than black

Answer

Hoses that show slight discoloration from engine heat exposure

Answer

Lines that are routed within 6 inches of the exhaust system

Question 7

What is the significance of the 'cut-in' and 'cut-out' pressures of the air compressor governor?

Accepted Answer

Cut-in (~100 psi) is when the compressor starts building pressure; cut-out (~125 psi) is when it stops to prevent over-pressurization

Answer

Cut-in is when spring brakes apply; cut-out is when they release

Answer

Cut-in is the minimum pressure for safe driving; cut-out is the pressure at which the warning light turns off

Answer

Cut-in and cut-out refer to when the primary and secondary circuits switch roles