by BT Alo
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In a vehicle, the thermal energy of the engine is converted into kinetic energy to allow it to move. When it comes to stopping movement, the same must be done in reverse: kinetic energy must be converted into thermal energy, stopping the vehicle. This is accomplished using friction devices called brakes. Most of today’s light vehicles use hydraulic fluid brakes while most heavy duty vehicles use brakes that work with compressed air.
A hydraulic brake contains a special brake fluid in the cylinders that compresses when the brake pedal is depressed, delivering pressure to friction components near the wheels which then press against each other to stop the vehicle. This process has a serious drawback: if there is a leak in the brake system that results in a partial or total loss of brake fluid, the efficiency of the brake system is significantly reduced or even completely lost. Air brakes solve this problem by using air instead of any special brake fluid to apply pressure to the braking components. Since air is freely available everywhere on the earth’s surface, this significantly reduces the chance of brake failure due to leaks in the braking system. This is the main reason why the use of air brakes is mandatory under government regulations for vehicles that exceed a certain size or that carry passengers for commercial purposes.
Air brakes are much more reliable than hydraulic brakes. First of all, most modern air brakes operate on a principle known as a triple valve system, as explained in the SDRM.org Train Air Brake Description and History article, which is designed in the opposite way. to hydraulic brakes or even to previously used types of air brakes. In a conventional braking system, the brake is in its default released position and is activated only when the brake fluid is compressed. However, the air brakes of the triple valve system are in the activated state by default and are released only with compressed air pressure. When the vehicle is started, compression begins and the brakes are released when the vehicle is put in motion. Therefore, if there is a leak or even if the compression mechanism fails completely, the brakes return to their default activated position and the vehicle comes to a stop.
The special brake fluid used in hydraulic brakes is quite expensive. Air, on the other hand, is freely available. While this doesn’t make much of a difference in small vehicles that require little hydraulic brake fluid, it does matter significantly in larger vehicles like heavy trucks and locomotives that would require large amounts of fluid if hydraulic brakes were used.