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What are vacuum pipes for?

Vacuum pipes can be seen on the front and rear of many older railway locomotives and rolling stock. They are usually located either on or around the buffer beam and are used to provide a 'through' vacuum to operate the train's braking system.
Vacuum brakes were introduced in the 1860s. Before then, trains were braked using a basic handbrake system which was slow to apply and required a member of railway staff per wagon. Needless to say, that setup meant accidents were commonplace and a more sophisticated system was needed.
Using vacuum as the power to operate individual brake cylinders was a natural choice as the ejectors (already used on steam locomotives) can be used to generate vacuum without complicated or moving parts. The vacuum pipes on the ends of locos, wagons and coaches are connected when a train is marshalled to provide a vacuum supply to all of the brakes throughout a train. 
Although the new system now gave drivers the ability to apply the brakes to a whole train with the use of a single valve, it still required the locomotive to be attached and operational to operate. That was a problem as coupling breakages were commonplace back then and a runaway section of the train would lose its vacuum supply (and therefore its braking) when the train separated.
To combat the problem, engineers started using the vacuum to hold brakes off as opposed to pulling them on. This method became known as automatic vacuum braking and was advantageous because if a pipe was to separate mid-journey, the vacuum would be lost and the spring-loaded brakes would automatically apply, thus stopping the train.

The system worked and was failsafe, however, it was also expensive and railway companies were reluctant to install it voluntarily. It wasn't until a horrific rail crash at Armagh in 1889 that automatic vacuum brakes became mandatory and remained the standard until air brakes replaced them in the 1970s.

Posted in: Rolling stock

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