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Air Pressure?

Discussion in 'Questions From New Drivers' started by FatBird11, Mar 5, 2019.

  1. Mar 5, 2019 #1
    FatBird11

    FatBird11 Bobtail Member

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    My CDL study book says, "Pushing the pedal down harder applies more air pressure."

    Then it goes on to say, "Letting up on the brake pedal reduces the air pressure and releases the brakes. "

    I was under the impression that the "more air pressure," the more relaxed the brakes.

    I thought the "reduction of air pressure," leads to the engagement of brakes.

    Doesn't the higher air pressure keep the brakes from engaging? If that's true, shouldn't the first sentence of this post read that "Pushing the pedal down harder applies less air pressure"?

    Maybe I'm just having a moment.

    Thanks,
    Bird
     
    FatBird11, Mar 5, 2019
    FatBird11, Mar 5, 2019
    #1
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  3. Mar 5, 2019 #2
    Ridgeline

    Ridgeline Road Train Member

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    OK there are two parts to this, the first is the parking brake and the other is the service brake.

    The parking brake needs air applied to release the brakes, it is a "safety" feature.

    Parking brake chambers are piggybacked onto the service chambers.

    Service cambers work when air is applied, it pushed the same connecting rod to the adjusters to apply the brakes, the more pressure on the brake pedal, the more pressure in the service chambers.

    You should have an illustration in your CDL manual that shows you how it works.
     
    Ridgeline, Mar 5, 2019
    Ridgeline, Mar 5, 2019
    #2
    bottomdumpin, FatBird11 and brian991219 Thank this.
  4. Mar 5, 2019 #3
    Tombstone69

    Tombstone69 Road Train Member

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    Picture your brake pedal as a water spicket,as you open the spicket more water comes out, same with a brake pedal pressing down on the pedal allows more air to go to the brake chambers.When you let up on the pedal, air is released through the release valves, can't make it any simpler than that.
     
    Tombstone69, Mar 5, 2019
    Tombstone69, Mar 5, 2019
    #3
    bottomdumpin and FatBird11 Thank this.
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