Fluid control valve

A control system for controlling the supply of pressurized fluid to a working element, such as a pneumatic spring, which valve comprises a housing having a bore comprising first and second bore sections with a middle bore section of smaller diameter between the first and second sections;

• a first passage in the housing for connection to a source of said pressurized fluid and communicating with said first bore section;
• an outlet opening in the housing and communicating with said second bore section;
• a second passage in the housing for connection to said working element and communicating with said middle bore section;
• a valve stem sealingly guided in said middle bore section and displaceable in accordance with a controlled variable of said working element, the valve stem having a duct therethrough communicating at one end with said second bore section;
• a valve closure member which is slidably guided in said first bore section towards the said valve stem and towards a shoulder at the boundary between said first and middle bore sections, the closure member having seating means for closure of said duct in said valve stem and for seating against said shoulder;
• the said seating means of said closure member being movable away from said shoulder to open a path for conduction of the pressurized fluid from said first to said middle bore section along the surface of said middle bore section;
• a throttle in said conduction path, which throttle is operative in dependence upon the position of the valve stem, the throttle being operative for a small deviation of said controlled variable from a datum, but being inoperative for a large deviation, the end of said valve stem remote from said valve closure member being urged by spring pressure against an abutment which is adjustably attached to said working element;
• and said abutment being subject to a spring pressure which limits the control range in one direction.