In turn the master brake cylinder develops hydraulic pressure in the wheels.

However, soon joined the brake cylinder, and still in use.

On the conventional side, the control valve set a reference pressure in a volume, which set brake cylinder pressure via a relay valve.

Braking force was translated into pressure that was sent to the rear brake cylinder.

These valves responded to a rise in train pipe pressure as the brake was applied, and admitted atmospheric air directly to the underside of the brake cylinder.