Automatic return mechanism for sliding door or window

Apparatus for automatically returning sliding closure to a predetermined position within a stationary frame, comprising:

• a cable anchor on said frame;
• a hollow housing on said sliding closure having a plurality of fixed partitions therein defining first and second axially aligned elongated compartments in said housing, said second compartment being more distant from said anchor and fluid-tight;
• a traveling block axially movably disposed in said first compartment;
• a cable from said anchor reeved through at least one sheave in said traveling block and secured to said partition closest to said anchor, such that as said closure is moved from said predetermined position, said traveling block is drawn toward said anchor;
• tensioning means connecting said traveling block with an intermediate partition between said first and second compartments and biasing said traveling block away from said anchor and adapted to prevent shock in the system when slack is introduced into the cable by manual movement of the closure;
• a longitudinal septum dividing said second compartment into first and second fluid-tight chambers having fluid communication conduits between their adjacent ends;
• a rod longitudinally movably disposed through said traveling block and said intermediate partition into said first chamber, travel of said rod bounded by the side of said traveling block away from said first chamber;
• biasing means biasing said rod and said traveling block away from said anchor;
• a movable valve mounted on said rod to regulate fluid flow between the opposite ends of said first chamber, said valve blocking or restricting longitudinal fluid flow within said first chamber when said closure moves from said predetermined position and permitting flow when said closure moves toward said predetermined position;
• and
• said valve and said fluid communication conduits cooperating to control the speed of movement of said rod urged by biasing of said second biasing means;
• whereby said closure is returned to said predetermined position at a preselected speed.