A two-pressure brake control valve has a service brake portion which is connected to a brake line, an auxiliary reservoir,an emergency reservoir and a brake cylinder. A main piston in the service brake portion is subjected to brake line pressure on one side and on its other side is subjected to pressure...http://www.google.fr/patents/US4063784?utm_source=gb-gplus-shareBrevet US4063784 - Two-pressure brake control valve for airbrakes
