Which air-brake system does the foot pedal normally operate when you slow for traffic?
Correct answer: The service brake system
The service brakes provide normal braking through the foot pedal. Parking and emergency functions have different roles.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1, physical PDF 79, printed 5-1. ↗
What supplies compressed air to the brake reservoirs while the engine is running?
Correct answer: The air compressor
The engine-driven compressor supplies air to the storage tanks. The other parts do not replenish the air supply.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.1, physical PDF 79, printed 5-1. ↗
Tank pressure falls to the compressor's specified cut-in point. What should the governor allow next?
Correct answer: The compressor to resume pumping air
The governor starts air pumping at cut-in and stops it at cut-out. Use the pressure specifications for the vehicle rather than assuming every system has identical settings.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.2, physical PDF 79, printed 5-1. ↗
Why can properly charged air brakes still make several applications after the compressor stops?
Correct answer: The reservoirs hold a reserve of compressed air
Air already stored in the reservoirs permits a limited number of brake uses. It is a reserve, not permission to keep driving with a failed compressor.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.3, physical PDF 79, printed 5-1. ↗
Water has collected in a brake air tank before freezing weather. What is the main brake-system risk?
Correct answer: It can freeze and interfere with brake operation
Compressed air can carry water that collects in tanks. Frozen moisture can make brake components fail, which is why tank drainage matters.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.4, physical PDF 79, printed 5-1. ↗
Your truck has manually operated air-tank drains, not automatic drains. When does the guide tell you to drain the tanks?
Correct answer: At the end of each day of driving
Manual drains must be operated at the end of each driving day to remove collected water and oil. Follow the equipment's safe draining procedure.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.4, physical PDF 79, printed 5-1. ↗
A truck has an alcohol evaporator and manual air-tank drains. Does the evaporator eliminate the need for daily draining?
Correct answer: No; water and oil still need to be drained
An alcohol evaporator helps reduce freezing in the air system. It does not remove the daily drainage requirement for manually drained tanks.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.5, physical PDF 80, printed 5-2. ↗
The brake-system safety relief valve begins releasing air. How should you treat this?
Correct answer: As a fault that needs a mechanic's attention
The relief valve protects the system against excessive pressure. Air release from it indicates a problem; do not block this safety device.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.6, physical PDF 80, printed 5-2. ↗
Why should a driver avoid repeatedly pressing and releasing the air-brake pedal when it is unnecessary?
Correct answer: It can use stored air faster than it is replaced
Releasing the brakes exhausts air. Unnecessary repeated applications can deplete the supply faster than the compressor restores it.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.7, physical PDF 80, printed 5-2. ↗
In an S-cam drum brake, what does the turning cam make the brake shoes do?
Correct answer: Move outward against the inside of the drum
The S-shaped cam spreads the shoes against the drum's inner surface. Friction at that contact slows the wheel.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.8, physical PDF 80, printed 5-2. ↗
You want to check the air available in the reservoirs, not the force of your current brake application. Which gauge provides that information?
Correct answer: The supply pressure gauge
Supply gauges show stored air pressure. A dual system has indications for both sides, sometimes through two needles in one gauge.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.9, physical PDF 80, printed 5-2. ↗
On a truck equipped with an application pressure gauge, what does its reading describe?
Correct answer: Air pressure being applied to the brakes
An application gauge shows the pressure used for a brake application. It is different from a supply gauge that indicates reservoir pressure.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.10, physical PDF 80, printed 5-2. ↗
