Think You Can Supply Air to Trailer Tanks? Take the CDL Air Brakes Quiz!
Air braking takes more time than hydraulic braking because air? Dive in to find out!
This CDL Air Brakes quiz helps you practice how to supply air to trailer tanks the right way. Answer quick, real-world items on brake chamber fill time, safety checks, and why spring brakes stay released with air; use it to spot gaps before the exam and review how spring brakes create stopping force and key CDL basics .
Study Outcomes
- Supply Air to Trailer Tanks -
Apply the correct procedure to you supply air to the trailer tanks by using the tractor protection valve, trailer air supply knob, and monitoring gauge readings to achieve proper pressure before driving.
- Explain Air vs. Hydraulic Braking Response -
Explain why air braking takes more time than hydraulic braking because air compresses, affecting brake response and requiring drivers to anticipate stopping distances.
- Identify Spring Brake Holdback -
Describe how during normal driving spring brakes are usually held back by air pressure, preventing premature activation and ensuring consistent braking performance.
- Use Parking Brakes Properly -
Demonstrate when and how with air brake vehicles the parking brakes should be used to secure parked rigs and prevent unintended movement.
- Assess Front Wheel Brake Performance -
Evaluate why front wheel brakes are good under all conditions, delivering reliable stopping power and stability across various road surfaces.
- Master Air Brake System Operations -
Apply the knowledge gained from the quiz to confidently inspect, test, and operate air brake systems ahead of the real CDL Air Brakes exam.
Cheat Sheet
- Supplying Air to Trailer Tanks -
When you supply air to the trailer tanks by pushing in the trailer air supply control, you open the tractor protection valve and allow compressed air to fill the trailer reservoirs from the tractor's supply lines. Always confirm a full charge by watching the green "supply" light and listening for the air build-up, which typically takes around 45 - 60 seconds in a dual-circuit system. Mnemonic: "Pull In, Press Out, Tanks Fill with a Shout!" helps you remember the correct push - pull sequence.
- Air vs. Hydraulic Braking -
Air braking takes more time than hydraulic braking because air must be compressed before pressure builds enough to actuate the brake chambers, so drivers need to anticipate stops early and maintain larger following distances. The compressibility of air adds a slight delay, meaning fully loaded rigs can require 20 - 40% more stopping distance compared to hydraulic systems. Pro tip: add one second of following distance for every ten feet of vehicle length at speeds above 40 mph.
- Spring Brake Holdback Mechanics -
During normal driving spring brakes are usually held back by air pressure acting against a powerful spring in the brake chamber, preventing the brake shoes from engaging until service brake pressure drops. If air pressure falls below 20 - 45 psi, the spring forces expand, automatically applying the brakes for emergency or parking functions. Remember the phrase "Air In, Spring Free; No Air, Spring Stops Me" to recall how spring-brake holdback works.
- Proper Use of Parking Brakes -
With air brake vehicles the parking brakes should be used every time you park by pulling the yellow control knob out, which vents the air and lets the spring brakes engage mechanically, securing your vehicle. Always wait until system pressure drops and the dash indicator confirms spring-brake activation before exiting the cab. This vital step is emphasized in FMCSA regulations and most state CDL manuals to prevent dangerous rollaways.
- Front Wheel Brake Application -
Front wheel brakes are good under all conditions thanks to weight transfer during braking, which increases traction on the front axle, but over-applying them can still cause wheel lockup on slick surfaces. Apply pressure smoothly and avoid sudden, hard pushes; a handy mnemonic is "Squeeze, Don't Snatch" to maintain control and prevent skids. According to SAE research, balanced brake usage optimizes stopping distance and vehicle stability.