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2. Commercial driver's license - Wikipedia

   en.wikipedia.org/wiki/Commercial_driver's_license

   A commercial driver's license is required to operate a tractor-trailer for commercial use. A commercial driver's license (CDL) is a driver's license required in the United States to operate large and heavy vehicles (including trucks, buses, and trailers) or a vehicle of any size that transports hazardous materials or more than 15 passengers (including the driver).

3. Relay valve - Wikipedia

   en.wikipedia.org/wiki/Relay_valve

   A relay valve is an air-operated valve typically used in air brake systems to remotely control the brakes at the rear of a heavy truck or semi-trailer in a tractor-trailer combination. Relay valves are necessary in heavy trucks in order to speed-up rear-brake application and release, since air takes longer to travel to the rear of the vehicle ...

4. Engine braking - Wikipedia

   en.wikipedia.org/wiki/Engine_braking

   A compression release brake (also known as a Jacobs brake or "jake brake"), is the type of brake most commonly confused with real engine braking; it is used mainly in large diesel trucks and works by opening the exhaust valves at the top of the compression stroke, so the large amount of energy stored in that compressed air is not returned to ...

5. Johnson bar (vehicle) - Wikipedia

   en.wikipedia.org/wiki/Johnson_bar_(vehicle)

   A Johnson bar activated parking/emergency brake on a 1930s White transit bus. Johnson bar is the term for several different hand-operated levers used in vehicles. Their distinguishing feature is a positive latch, typically spring-loaded, to hold the lever in a selected position, capable of being operated with one hand.

6. Retarder (mechanical engineering) - Wikipedia

   en.wikipedia.org/wiki/Retarder_(mechanical...

   Exhaust brakes are simpler in operation than an engine brake.Essentially, the exhaust pipe of the vehicle is restricted by a valve.This raises the pressure in the exhaust system, forcing the engine to work harder on the exhaust stroke of its cylinders, so again the engine is acting as an air compressor, with the power required to compress the air being withheld from the exhaust pipe, retarding ...

7. S-cam - Wikipedia

   en.wikipedia.org/wiki/S-cam

   An S-cam is part of a braking system used in heavy vehicles such as trucks and wheeled machinery. It consists of a shaft, usually around 4 to 25 inches long, turned at one end by means of an air-powered brake booster and lever with an S-shaped cam at the wheel end.