Hydraulic positioner with bidirectional detenting action

An hydraulic positioner of the type in which a piston is movable within a fluid-filled cylinder, for adjustment to a given separation between its attachment points and for thereafter maintaining the given separation, having a bidirectional detenting action whereby the given separation can be altered only by application of a sufficiently large overriding force, said hydraulic positioner comprising:

• a cylinder, hollow and having a central axis, open at its first and second ends, and having an inwardly-facing bore surface;
• piston means, slidable axially within said cylinder, having a first side facing in a first axial direction and having a second side facing in a second axial direction opposite the first axial direction, and having a peripheral portion adjacent the bore surface of said cylinder but spaced from it;
• a first rod attached to the first side of said piston means and extending in said first axial direction;
• a second rod attached to the second side of said piston means and extending in said second axial direction;
• first stationary sealing means positioned in said cylinder near its first end, in slidable sealing engagement with said first rod and forming a first sealed chamber for containing fluid within said cylindrical between said first stationary sealing means and said piston means;
• second stationary sealing means positioned within said cylinder near its second end, in slidable sealing engagement with said second rod and forming a second sealed chamber for containing fluid within said cylinder between said second stationary sealing means and said piston means;
• first check valve means associated with said piston means for movement therewith, preventing fluid from passing through it from said second sealed chamber to said first sealed chamber, and passing fluid from said first sealed chamber to said second sealed chamber when a force in excess of a predetermined force is applied to said piston means in said first direction;
• second check valve means associated with said piston means for movement therewith, preventing fluid from passing through it from said first sealed chamber to said second sealed chamber, and passing fluid from said second sealed chamber to said first sealed chamber when a force in excess of a predetermined force is applied to said piston means in said second direction;
• a reservoir for fluid, including a closed chamber extending in the second direction beyond the second end of said cylinder;
• and,
• means for pressurizing fluid in said reservoir;
• said second rod extending through said second stationary sealing means and beyond the end of said cylinder into said reservoir, said second rod further comprising an internal passage extending through it between two ports spaced sufficiently far apart in the axial direction to permit communication of pressurized fluid through said second rod from said reservoir to said second sealed chamber so that said second sealed chamber is pressurized at a small positive pressure and so that pressurized fluid is supplied from said reservoir to said second sealed chamber to replace leakage.