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) ↗
