page_title: Vacuum brake
section_title: Ejectors
hierarchical_section_title: Vacuum brake / Producing the vacuum / Ejectors
caption_attribution_description: English: Earl of Merioneth at Porthmadog Harbour railway station
context_page_description: The vacuum brake is a braking system employed on trains and introduced in the mid-1860s. A variant, the automatic vacuum brake system, became almost universal in British train equipment and in countries influenced by British practice. Vacuum brakes also enjoyed a brief period of adoption in the United States, primarily on narrow-gauge railroads. Its limitations caused it to be progressively superseded by compressed air systems starting in the United Kingdom from the 1970s onward. The vacuum brake system is now obsolete; it is not in large-scale usage anywhere in the world, other than in South Africa, largely supplanted by air brakes.
context_section_description: Vacuum brakes were initially favoured over air brakes because of the ease of producing the vacuum. A vacuum ejector was a simpler and reliable device, compared to the reciprocating pump.
  Typically two ejectors are fitted, large and small. The large ejector is used to 'blow off' the brakes, by producing the vacuum, and is then shut off. The small ejector is left running continuously in order to maintain it. The Gresham & Craven 'Dreadnought' ejector was a combination ejector, with both large and small ejectors within the same body. The vacuum produced depended on the total number of vehicles in the train and the sum of their various minor leaks. A train of stock due for maintenance could make it difficult to maintain a vacuum, even requiring intermittent use of the large ejector when running. The widely used Super-Dreadnought ejector combined a large ejector with two small ejectors in one. If needed, two of the smaller nozzles could produce more vacuum, yet were more efficient in their use of steam then  a single larger nozzle.
  The Great Western Railway was noted for its idiosyncrasies, including the use of a higher brake vacuum than other lines. To maintain this without excessive steam consumption in an ejector, they also favoured the use of a crosshead-driven mechanical pump.
caption: Driver's brake control on a combined control and ejector. The ejector steam nozzles, large and small, are beneath the hexagonal brass plugs on the left.
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