An accelerator device for a three-pressure control valve of an air brake system on a railway vehicle has a control piston one side of which is subjected to air line pressure and the other side to pressure in a control chamber such that when the pressure in the control chamber predominates the control piston opens an accelerator valve between the air line pressure and a valve chamber. A monitor valve is between the valve chamber and a transfer chamber which continuously communicates to the atmosphere through a throttle orifice. A first piston operates the monitor valve and is subjected in the closing direction of the monitor valve to the action of braking pressure against the effect of a spring force. A second piston which is coupled to the first piston is loaded by air-line-pressure acting in the closing direction of the monitor valve against the pressure in a chamber which can be filled with air line pressure through a check valve opening in the direction of flow of the air line pressure and having a throttle orifice therein.
The acceleration apparatus for connection with a pilot operated compressed-air brake comprises a tap-off valve which vents the main air line or conduit at the beginning of the braking procedure. This tap-off valve is opened by an actuator or actuating mechanism via a disengageable intermediary member. By employing a rotationally symmetrical plunger or push rod which is pivoted into the operative position thereof by a spring and deflected by an interrupter piston, the construction of the disengageable intermediary member can be substantially simplified. The plunger or push rod possesses at the one end thereof a cam or pin and a substantially conical surface.
