vacuum brake

noun1

1. •
   A brake used on trains, working on the principle of keeping up a vacuum in a continuous pipe or pipes extending under the train, and in brake-cylinders connected to them under each vehicle, the air being sucked out by ejectors or pumps on the locomotive.

   • Compressed air is used for the operation of certain contactors, the sanders, the horn, and the re-fuelling equipment, but vacuum brakes are fitted to the locomotive. — 1951