Railway brake
In the United Kingdom, the Abbots Ripton rail accident in January 1876 was aggravated by the long stopping distances of express trains without continuous brakes, which – it became clear – in adverse conditions could considerably exceed those assumed when positioning signals.
In the words of a contemporary railway official, these showed that under normal conditions it required a distance of 800 to 1200 yards to bring a train to rest when travelling at 45½ to 48½ mph, this being much below the ordinary travelling speed of the fastest express trains.
Railway officials were not prepared for this result and the necessity for a great deal more brake power was at once admitted[3] Trials conducted after Abbots Ripton reported the following for an express train roughly matching conditions involved (such as a 1 in 200 downward run, but not braking under favorable conditions):[2] However, there was no clear technical solution to the problem, because of the necessity of achieving a reasonably uniform rate of braking effort throughout a train, and because of the necessity to add and remove vehicles from the train at frequent points on the journey.
The chief types of solution were: Note: there are a number of variants and developments of all these systems.
The Newark trials showed the braking performance of the Westinghouse air-brakes to be distinctly superior:[14] but for other reasons[15] it was the vacuum system that was generally adopted on UK railways.
These hand brakes were used where necessary when vehicles were parked but also when trains were descending a steep gradient.
[18] As train loads, gradients and speeds increased, braking became a more significant problem.
These continuous brakes can be simple or automatic, the essential difference being what happens should the train break in two.
Simple non-automatic brakes are thus useless when things really go wrong, as is shown with the Armagh rail disaster.
Most tractive units, passenger coaches and some freight wagons are equipped with a hand-operated parking brake (handbrake).
A manually operating parking brake is only suitable for securing static railway vehicles from rolling away.
Visual differences between the two systems are shown by air brakes working off high pressure, with the air hoses at the ends of rolling stock having a small diameter; vacuum brakes work off low pressure, and the hoses at the ends of rolling stock are of a larger diameter.
The brake works by using the cylinders as air compressors and converting kinetic energy into heat.
It also allows for faster brake application, as the electrical control signal is propagated effectively instantly to all vehicles in the train, whereas the change in air pressure which activates the brakes in a conventional system can take several seconds or tens of seconds to propagate fully to the rear of the train.
[citation needed] Electronically controlled pneumatic brakes (ECP) are an American development of the late 20th Century to deal with very long and heavy freight trains, and are a development of the EP brake with even higher level of control.
In addition, information about the operation of the brakes on each wagon is returned to the driver's control panel.
Electrical control signals are propagated effectively instantaneously, as opposed to changes in air pressure which propagate at a rather slow speed limited in practice by the resistance to air flow of the pipework, so that the brakes on all wagons can be applied simultaneously, or even from rear to front rather than from front to rear.
This causes the brake clips to be applied on individual wagons, assisted by a servo system which makes use of the rotation of the axle.
On the new Fortescue railway opened in 2008, wagons are operated in sets, although their direction changes at the balloon loop at the port.
