Spool valve assembly

Claim 1

A SPOOL VALVE ASSEMBLY COMPRISING A HOUSING FORMED WITH A BORE INTERSECTED AXIALLY THEREALONG BY A PRESSURE INLET PORT, A TANK PORT, AND A PAIR OF SERVICE PORTS ADAPTED FOR CONNECTION WITH A HYDRAULIC CYLINDER ASSEMBLY TO RAISE AND LOWER A LOAD ON THE PISTON THEREOF; A HOLLOW VALVE SPOOL AXIALLY RECIPROCABLE IN SUCH BORE AND FORMED WITH ALTERNATE LANDS AND GROOVES AND WITH OPENINGS THROUGH CERTAIN LANDS THEREOF TO PROVIDE A NEUTRAL POSITION WHEREAT SAID INLET AND TANK PORTS ARE IN FLUID COMMUNICATION AND SAID SERVICE PORTS ARE BLOCKED BY LANDS OF SAID SPOOL, TWO OPERATING POSITIONS WHEREAT SAID INLET AND TANK PORTS ARE COMMUNICATED SELECTIVELY WITH SAID SERVICE PORTS TO ACTUATE SUCH CYLINDER ASSEMBLY IN EITHER DIRECTION; AND A FLOAT POSITION WHEREAT SAID SERVICE PORTS ARE COMMUNICATED WITH EACH OTHER AND SAID INLET AND TANK PORTS ARE COMMUNICATED WITH EACH OTHER; AND RESTRICTOR MEANS EFFECTIVE, IN ONE OPERATING POSITION ONLY, TO BUILD UP A BACK PRESSURE IN ONE SERVICE PORT WHEN THAT SERVICE PORT IS COMMUNICATED WITH SAID TANK PORT; SAID RESTRICTOR MEANS COMPRISING A PERFORATE SLEEVE MOUNTED IN SAID HOUSING TO CONSTITUTE AN EXTENSION OF SUCH BORE AND THROUGH WHICH FLUID FLOWS FROM SAID ONE SERVICE PORT TO SAID TANK PORT.