OPERATION - Schematic of Vacuum Brake Circuit with the Brakes Shown in the On Position

• The ejector or vacuum pump draws the air from the train pipe, the brake cylinder and the reservoir (via the none-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 none 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.

PNP Railways are able to offer a complete vacuum braking system, which includes: Vacuum Actuator Kits, Vacuum Reservoir Kits, Brake Blocks, Limiting and Release Valves, Progressive Brake Valve, Vacuum Gauges, Vacuum Ejectors and Vacuum Pump.