Schematic of the Vacuum Braking System

How they Work:

  • The ejector or vacuum pump draws the air from the train pipe, the brake cylinder and the reservoir (via the non-return valve).
  • The brakes will then be off and the system will be in equilibrium.
  • The brakes will be kept off by being weight biased or lightly sprung. Please refer to the diagram.
  • Letting air back into the train pipe via the drivers brake valve or a pipe disconnection the air pressure acting on the underside of the piston or, in this case diaphragm, will push the piston up and pull on the brakes.
  • Since the vacuum on the upper side of the piston is trapped by the non-return valve the vacuum must be recreated in the train pipe to release the brakes.
  • Similarly when the loco is removed and the brakes need to be released to shunt the train this trapped vacuum can be destroyed by opening the release valve.