Empty-load changeover valve for railway car

A changeover valve device interposed between a control valve and a vehicle brake cylinder for adjusting the brake cylinder pressure according to the vehicle load condition comprising:

• (a) load sensing means for providing a load setting of said changeover valve device when the load of said vehicle exceeds a predetermined value and for providing an empty setting of said changeover valve when the load of said vehicle is less than said predetermined value;
• (b) an inlet passage connected to said control valve and an outlet passage connected to said brake cylinder;
• (c) proportioning valve means including:
• (i) a first valve seat between said inlet and outlet passages;
• (ii) a first valve element between said first valve seat and said outlet passage, said first valve element being engageable with said first valve seat in a closed position to interrupt fluid pressure communication between said inlet and outlet passages and disengageable therefrom in an open position to establish fluid pressure communication between said inlet and outlet passages;
• and
• (iii) a balance piston to which said first valve element is connected having equal opposing pressure areas, one of said pressure areas being subject to the fluid under pressure effective at said inlet passage;
• (d) empty/load valve means for supplying the fluid under pressure at said inlet passage to the other of said pressure areas of said balance piston in said load setting of said changeover valve device to establish a force balance across said piston member, and for venting fluid under pressure acting on said other pressure area in said empty setting of said changeover valve device to establish a differential force across said balance piston in the direction of engagement of said first valve element with said first valve seat;
• and
• (e) lock-out means for interrupting said supply and venting of fluid under pressure effective at said other pressure area of said balance piston when said differential force across said balance piston is sufficient to cause said balance piston to effect said engagement of said first valve element with said first valve seat.