Variable load valve for railway vehicles

A variable load valve device for a railway vehicle comprising:

• (a) a supply passage to which a source of fluid under pressure is connected;
• (b) an output passage to which a fluid pressure operated brake cylinder device of the vehicle is connected;
• (c) an exhaust passage connected to atmosphere;
• (d) a valve assembly including:
• (i) a valve member;
• (ii) a supply valve seat between said supply passage and said output passage with which said valve member coacts to control the supply of fluid under pressure to said brake cylinder device;
• (iii) an exhaust valve seat between said output passage and said exhaust passage with which said valve member coacts to control the exhaust of fluid under pressure from said brake cylinder device;
• and
• (iv) means for urging said valve member toward engagement with said supply valve seat;
• (e) a balancing chamber to which said output passage is connected;
• (f) a piston member including:
• (i) said exhaust valve seat;
• (ii) a balancing piston having a first pressure area subject to said balancing chamber fluid under pressure to urge said piston member in a first axial direction to effect disengagement of said exhaust valve seat from said valve member;
• and
• (iii) a control piston having a second pressure area subject to a command fluid pressure to urge said piston member in a direction opposite said first axial direction to effect engagement of said exhaust valve seat with said valve member and to effect disengagement of said valve member from said supply valve seat, said valve assembly having a lap condition in which said valve member is engaged with said supply valve seat and said exhaust valve seat when a force balance exists across said piston member;
• (j) means for varying said first pressure area of said piston member in accordance with the axial position of said piston member in said lap condition of said valve assembly;
• (k) an intermediate member including said supply valve seat, said intermediate member being axially movable to accordingly change the axial position of said piston member in said lap condition of said valve assembly;
• and
• (l) advancing/retracting means for automatically effecting said axial movement of said intermediate member in response to different load conditions of said vehicle.