Valve for controlling pressure medium actuated brakes for railway and other vehicles

Claim 1

A control valve for pressure medium actuated brakes for a railway or other vehicle and comprising a multi-stage axially displaceable stepped piston valve member having a plurality of annular radial surfaces thereon with a predetermined surface area ratio to one another, a double valve connected between a supply of pressure medium, a vent and a brake and operable by said piston valve member so that the pressure medium at the brake is controlled in response to the position of said double valve, a plurality of control valves selectively operable to subject said radial surfaces individually or in combination to said pressure medium at the brake in response to a selected pressure stage, and thereby exerting an axial force upon said piston valve member directed to open said vent via said double valve, and spring means acting upon said piston valve member for applying an axial force against said piston valve member independently of the pressure medium at the brake and in opposition to the force exerted by the pressure medium against said radial surfaces and directed to open a connection from said supply of pressure medium via said double valve to said pressure medium at the brake, such that said applied force and the force by said pressure medium are constant and balance each other at all stages of braking, said piston valve member has a radial surface opposed to said plurality of radial surfaces and said axial force applying means acts upon said opposed radial surface.