What is the air compressor’s job in an air brake system?
Correct answer: Pump air into the storage tanks
The compressor supplies compressed air to the reservoirs used by the brake system.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.1 Air Compressor, printed page 5-1 (physical PDF page 79) ↗
At approximately what tank pressure does the governor normally cut out the air compressor?
Correct answer: 125 psi
The governor normally stops compressor loading near 125 psi, although manufacturer specifications may vary.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.2 Air Compressor Governor; 5.3.3 manufacturer specifications on printed 5-6, printed page 5-1 (physical PDF page 79) ↗
At approximately what pressure does the governor normally allow the compressor to cut in again?
Correct answer: 100 psi
The governor normally restarts compressor loading near 100 psi. Check the manufacturer specifications for the particular vehicle; the final air-brake check uses those specified pressures.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.2 Air Compressor Governor; 5.3.3 manufacturer specifications on printed 5-6, printed page 5-1 (physical PDF page 79) ↗
Why must moisture and oil be removed from air storage tanks?
Correct answer: Water can freeze and interfere with braking
Water and oil collect in the tanks; frozen water can obstruct the system and cause brake failure.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.4 Air Tank Drains, printed page 5-1 (physical PDF page 79) ↗
When should manually drained air tanks normally be emptied?
Correct answer: At the end of each driving day
Manual tank drains should be opened completely at the end of each day of driving.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.4 Air Tank Drains, printed page 5-1 (physical PDF page 79) ↗
What does the air-system safety valve protect against?
Correct answer: Excessive pressure
The valve protects the first tank and the rest of the system from overpressure and usually opens near 150 psi.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.6 Safety Valve, printed page 5-2 (physical PDF page 80) ↗
Why should a driver avoid unnecessary repeated brake-pedal applications?
Correct answer: Air use may exceed compressor output
Each release exhausts compressed air, so repeated applications may lower pressure to an unsafe level.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.7 The Brake Pedal, printed page 5-2 (physical PDF page 80) ↗
What can increasing application pressure needed to hold the same speed indicate?
Correct answer: The brakes may be fading
A rising application-pressure requirement can signal brake fade, poor adjustment, leaks, or mechanical trouble.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.10 Application Pressure Gauge (continued), printed page 5-3 (physical PDF page 81) ↗
In the Florida handbook section 5.3.3 low-pressure warning check, the warning must activate before pressure falls below what threshold?
Correct answer: 55 psi
Section 5.3.3 specifies that the warning must come on before pressure falls below 55 psi in the tank, or the lowest-pressure tank of a dual system. Some vehicles warn earlier. Stop safely when a low-air warning occurs; do not wait for spring brakes.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Test Low Pressure Warning Signal, printed page 5-7 (physical PDF page 85) ↗
What holds spring brakes off while a vehicle is being driven normally?
Correct answer: Air pressure
Air pressure compresses the powerful springs; loss of pressure lets the springs apply the brakes.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.14 Spring Brakes, printed page 5-3 (physical PDF page 81) ↗
At what approximate pressure range do tractor and straight-truck spring brakes come fully on?
Correct answer: 20 to 45 psi
Spring brakes normally apply automatically as pressure falls into the 20-45 psi range.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.14 Spring Brakes, printed page 5-3 (physical PDF page 81) ↗
On a newer air-brake vehicle, how is the parking brake normally applied?
Correct answer: Pull out the yellow diamond-shaped control
Pulling out the yellow push-pull knob releases air from the spring brakes so they apply.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.15 Parking Brake Controls, printed page 5-3 (physical PDF page 81) ↗
Why should the foot brake not be pressed while spring brakes are already applied?
Correct answer: Combined spring and air forces may damage the brakes
Some systems can be damaged when air pressure adds to the force of applied spring brakes.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.15 Parking Brake Controls, Caution, printed page 5-3 (physical PDF page 81) ↗
If the ABS malfunction lamp stays on, what braking capability remains?
Correct answer: Normal braking remains, but ABS needs service
An ABS fault does not remove normal brakes; drive normally and arrange service promptly.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.4.2 Braking with Antilock Brakes, printed page 5-8 (physical PDF page 86) ↗
On a reachable S-cam slack adjuster, what manually pulled movement at the push-rod connection suggests a need for adjustment?
Correct answer: More than about one inch
With wheels chocked and parking brakes released, manually pulling a reachable S-cam slack adjuster more than about one inch at the push-rod connection signals trouble. This is not a universal applied push-rod stroke limit. Have faults repaired; routinely adjusting automatic adjusters is not a substitute for repair.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.2 Check Slack Adjusters on S-cam Brakes, printed page 5-6 (physical PDF page 84) ↗
During a one-minute applied leakage test, what is the maximum pressure drop for a single vehicle?
Correct answer: 3 psi
Secure the vehicle, charge the system, shut off the engine, and release the parking brakes. Fully apply the foot brake and let the initial pressure drop stabilize before timing one minute. A single vehicle must not then lose more than 3 psi.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Test Air Leakage Rate (continued from printed 5-6), printed page 5-7 (physical PDF page 85) ↗
During a one-minute applied leakage test, what is the maximum drop for a two-vehicle air-brake combination?
Correct answer: 4 psi
With both vehicles air-braked, secure the combination, charge the system, shut off the engine, and release parking brakes. Fully apply the foot brake. After the initial drop stabilizes, loss must not exceed 4 psi in one minute.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Test Air Leakage Rate (continued from printed 5-6), printed page 5-7 (physical PDF page 85) ↗
In the Florida section 5.3.3 static leakage check, what loss rate should a single vehicle stay below?
Correct answer: 2 psi in one minute
Secure the vehicle against rolling, fully charge the system, stop the engine and release the brakes. The chapter specifies a loss rate of less than 2 psi per minute for a single vehicle. This is the brakes-released test, not the applied test.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Test Air Leakage Rate, brakes released, printed page 5-6 (physical PDF page 84) ↗
At operating engine rpm, what buildup does Florida section 5.3.3 specify for a typical dual air system?
Correct answer: 85 to 100 psi within 45 seconds
Check at operating rpm. The handbook allows longer buildup for vehicles with larger-than-minimum air tanks; consult the manufacturer specifications. Do not apply the older single-system idle-speed test to this dual system.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Check Rate of Air Pressure Buildup, printed page 5-7 (physical PDF page 85) ↗
How should service brakes be checked after normal air pressure is restored?
Correct answer: Move forward slowly at about 5 mph and apply them firmly
A low-speed firm application can reveal pulling, unusual feel, or delayed stopping.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Test Service Brakes, printed page 5-7 (physical PDF page 85) ↗
