The Brake System – Adding Spring Brakes- Zhejiang Juda Electromechanical Technology Co., Ltd.

In the early days of air brakes, only "service Brakes" - the on-the-road brakes - were provided. Parking and/or "emergency" brakes were supplied by a drum or disk brake mounted on the drive shaft. Since total braking capacity is soon overwhelmed if heat buildup is allowed to occur, and since increasing total brake area is the major way to overcome this, it's best to use the rear service brakes as parking/emergency brake.

Enter the Spring Brake. These utilize the second system of brake actuation - only for the rear brakes - being applied by very strong springs, which duplicate the action of the otherwise air-operated brake chambers, by the addition of "Spring Brake Chambers".

Spring Brakes - Parking Brakes for Air-Equipped Vehicles

Since it would be ridiculous to expect an air chamber to maintain pressure over long periods of parking, the spring brake has just that - a spring applies the rear brakes, which are therefore always on unless the spring is "caged" by a second additional air chamber, "piggy-backed" onto the one already there for the regular service brakes. To de-apply the parking brakes, the system must first be brought up to pressure (the compressor), and then the spring chambers are charged with air by means of the dash-mounted parking brake valve. This offsets the springs and lets the vehicle move. (In most cases, there is also a mechanical means to cage the springs in case of emergencies - you get out and under, remove the dust cap, and screw the cage bolts up by hand.)

This kind of parking brake has a major difference from the brakes we're all used to - if the system loses its pressure, the de-application pressure is also lost, and the parking brakes will come on as the pressure decreases - providing an " automatic" setting of the parking brakes if system pressure is lost on the road. This is another reason we must pay attention to system pressure - if it drops to the danger level, you need to pull over in the first safe place, while you still have enough air to maintain control over your brakes, or you just may find yourself stopped in the middle of the freeway!

Important Safety Note!

Does this mean that you will always have an automatic emergency brake, which will come on every time you lose pressure? No, there is still one eventuality that will not - ever - be accounted for, and that is excessive adjuster slack! The final determinant in the airbrake equation is always the mechanical linkage between the air chamber/brake pot and the actuation lever - the slack adjuster. If an adjuster - or all of them - is too slack, no amount of spring or air pressure is going to put that brake on - the pushrod will move to its full extent, and 20,000 Lbs of coach will sail blithely on into whatever disaster awaits. NEVER let your adjusters get too slack! Check them daily, and more than that when you're using your brakes more than usual.

And don't ever forget, the rear brake slack must be done with the brake springs caged! - So you'll have to check your wheels and set your brake control to the "off" position.

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