Fluid controller and improved backflow prevention therefor

A fluid controller operable to control the flow of fluid from a source of pressurized fluid to a fluid pressure operated device, the controller being of the type including housing means including an inlet port for connection to the source of fluid, a return port for connection to a reservoir, first and second control fluid ports for connection to the fluid pressure operated device, valve means disposed in said housing means and defining a neutral position (FIG. 3) and at least one operating position (FIG. 5);

• means for imparting follow up movement to bias said valve means toward said neutral position in response to the flow of fluid to or from the fluid pressure operated device;
• said valve means cooperating with said housing means to define a first flow path communicating between said inlet port and said follow up means, a second flow path communicating between said follow up means and one of said control fluid ports, and a third flow path communicating between the other of said control fluid ports and said return port, said first, second, and third flow paths including first, second, and third variable flow control orifices, respectively, having a gradually increasing flow area as said valve means is moved towards said operating position (FIG. 5);
• said first variable orifice begins to open at a displacement X, and said second variable orifice begins to open at a displacement Y as said valve means moves from said neutral position toward said operating position, Y being greater than X;
• characterized by:
• (a) said valve means defines an additional second variable orifice disposed in said second fluid path, said additional second variable orifice begins to open at a displacement Y', said displacement Y' being less than said displacement X;
• and
• (b) said valve means including means operable to prevent fluid flow through said additional second variable orifice unless the fluid pressure in said first flow path is greater than the fluid pressure in said first control fluid port, said flow prevention means being operable to prevent reverse fluid flow from said first control fluid port through said additional second variable orifice to said follow up means.