An automatic fluid control valve for maintaining a substantially constant fluid flow rate comprising:
- a valve casing having an inlet for the introduction of fluid thereinto and an outlet for discharge of fluid therefrom;
- a partition wall within said casing between said fluid inlet and fluid outlet, said partition wall subdividing said valve casing into an inlet chamber and an outlet chamber, said partition wall having a lower horizontally extending portion in which a valve port is formed, said valve port establishing communication between said fluid inlet and said fluid outlet, said partition wall also having an upper horizontally extending portion having an opening therethrough in vertical alignment with said valve port;
- a valve steam movable linearly within said casing and being slidable within said valve port and said opening, said valve stem having valve means thereon cooperable with said valve port to regulate the flow of fluids therethrough in response to changes in fluid pressure differential, the lower portion of said valve stem carrying thereon an inner valve member comprising a cylindrical valve plug which is cooperable with said valve port and the uper portion of said valve stem carrying thereon a slide member, a guide bushing being positioned within the opening in said upper horizontally extending portion of said partition wall and said slide member being slidable on the inner peripheral surface of said guide bushing, a strainer positioned beneath said guide bushing coaxial with said valve stem and having an axial opening dimensioned to permit movement of said valve stem therethrough;
- diaphragm means operatively connected to the upper end of said valve stem and separating a region within said valve casing into a pair of pressure-differential chambers, said diaphragm defining together with an upper portion of said valve casing one of said pressure-differential chambers;
- a fluids passageway of variable cross-sectional area settable to establish a predetermined fluid flow rate through the control valve located intermediate said fluid inlet and said outlet and thereby establishing first and second fluid pressures respectively on the upstream and downstream sides of said fluidspassageway;
- said fluids passageway being positioned in the outlet of said valve casing;
- and
- conduit means communicating said valve casing outlet downstream of said fluids passageway with said one pressure-differential chamber, said inner valve member having a lower portion of lesser diameter than that of the valve plug and comprising a mounting member for mounting the inner valve member on said valve stem, said valve casing having a bottom plate in which there is formed an opening, a tube member positioned in said bottom plate opening and the outer peripheral surface of said mounting member being slidable on the inner peripheral surface of said tube member, said other pressure-differential chamber being located beneath said diaphragm external of said partition wall, said other pressure-differential chamber being in open communication with the upstream side of said fluids passageway, said strainer being exposed to the fluids entering the inlet of said valve casing to permit the passage of a portion of said fluids therethrough and through a clearance opening between said slide member and said guide bushing for introduction into said other pressure-differential chamber.