How should rear air-line shut-off valves be set in a doubles combination?
Correct answer: Lead trailer open; final trailer closed
Air must flow through intermediate units, while unused ends at the last trailer stay closed.
Source: Florida Commercial Driver's License Manual, July 2022, section 7.3.1 Double and Triple Trailers, shut-off valves, printed page 7-3 (physical PDF page 105) ↗
Which converter-dolly items require a secure inspection?
Correct answer: Pintle connections, chains, air lines, light cords
All dolly connections must be latched, supported, connected, and undamaged.
Source: Florida Commercial Driver's License Manual, July 2022, section 7.3.1 Double and Triple Trailers (continued), printed page 7-4 (physical PDF page 106) ↗
How is emergency-line airflow verified at the back of a doubles rig?
Correct answer: Charge the system and briefly open the last trailer’s emergency shut-off to hear escaping air
Secure the rig with the tractor parking brake and/or wheel chocks, charge the system, then briefly open and close the last emergency-line valve. Escaping air shows supply reaches the rear. Check service-line flow separately, and close each valve after testing.
Source: Florida Commercial Driver's License Manual, July 2022, section 7.4.1 Check That Air Flows to All Trailers, printed page 7-4 (physical PDF page 106) ↗
At approximately what pressure range does the trailer-air-supply control usually pop out during its test?
Correct answer: 20 to 45 psi
The exact value follows the manufacturer, but the handbook gives a usual 20-to-45-psi range.
Source: Florida Commercial Driver's License Manual, July 2022, section 7.4.1 Test Tractor Protection Valve, printed page 7-4 (physical PDF page 106) ↗
On a combination equipped with a trailer hand control, how should the trailer service brakes be tested?
Correct answer: Move forward slowly and apply the trailer hand control to feel the brakes engage
At normal air pressure with parking brakes released, move forward slowly and apply the hand control, if equipped. Feel the trailer brakes engage. Use the foot pedal for normal braking, not the hand control.
Source: Florida Commercial Driver's License Manual, July 2022, section 7.4.1 Test Trailer Service Brakes, printed page 7-4 (physical PDF page 106) ↗
