1.1 INTRODUCTION TO BRAKES
Brakes are mechanical devices that increase the frictional resistance that retards the turning motion that is supplied to the wheels of the vehicle. In a vacuum assisted hydraulic brake system, a constant vacuum is kept maintained in the brake booster using the engine. When the brake pedal is pushed down, a poppet valve opens and air pushes/rushes into the pressure chamber on the driver’s side of the booster. In a vacuum braking system, vacuum is used for the application of brakes.
Braking the train is a very complex process, particularly to rail vehicles and is of great importance because of essential contribution on the safety of the moving vehicle. This complexity comes into picture from…show more content… It was invented in 1870 in the USA at the time of air brake, where it enjoyed popularity only for a short period primarily on narrow gauge railroads. The system took a greater hold in the United Kingdom and was being used there as the primary form of train braking until the 1970s. Vacuum braking is for all practical purposes now almost a dead technology; it is not in very large-scale use anywhere in the world, supplanted in the main by air brakes. Vacuum brakes have now been largely superseded by air brakes that work on a similar principle but use compressed air instead of a vacuum. This allows for more braking power, since the pressure differential between atmospheric pressure and a feasible vacuum is less than that between atmospheric pressure and a realistic brake-pipe pressure.…show more content… This was clearly unsatisfactory, but the existing technology did not offer an improvement. A chain braking system was developed, requiring a chain to be coupled throughout the train, but it was impossible to arrange equal braking effort along the entire train.
A major advance was the adoption of a vacuum braking system, in which flexible pipes were connected between all the vehicles of the train, and brakes on each vehicle could be controlled from the locomotive. The earliest scheme was a simple vacuum brake, in which vacuum was created by operation of a valve on the locomotive; the vacuum actuated brake pistons on each vehicle, and the degree of braking could be increased or decreased by the driver. Vacuum, rather than compressed air, was preferred because steam locomotives can be fitted with ejectors; venturi devices that create vacuum without moving parts.
The simple vacuum system had the major defect that in the event of one of the hoses connecting the vehicles becoming displaced (by the train accidentally dividing, or by careless coupling of the hoses, or otherwise) the vacuum brake on the entire train was