Servo operated hydraulic valves

Claim 1

A SERVO-OPERATED HYDRAULIC SLIDE VALVE, COMPRISING A VALVE HOUSING HAVING A CYLINDRICAL BORE CLOSED AT EACH END BY AN END WALL HAVING A BORE COAXIAL WITH SAID CYLINDRICAL BORE, A CYLINDRICAL SPINDLE EXTENDING THROUGH THE HOUSING AND SEALINGLY MOUNTED IN THE BORES OF SAID END WALLS FOR ROTATION WITHOUT AXIAL MOVEMENT, SAID SPINDLE HAVING, INSIDE THE HOUSING, TWO HELICAL GROOVES OF EQUAL MAGNITUDE AND SENSE OF HELICAL PITCH RESPECTIVELY COMMUNICATING WITH A CLOSED BORE AND, A SPOOL-TYPE SLIDEVALVE SLEEVE HAVING TWO INNER AND TWO OUTER EXTERNAL LANDS AXIALLY SPACED FROM EACH OTHER AND SLIDABLY AND SEALINGLY FITTED IN THE BORE OF THE HOUSING AND SEALINGLY ENGAGING THE SPINDLE THROUGHOUT THE LENGTH OF THE SLEEVE, AND TWO DIAMETRICALLY OPPOSITE APPROXIMATELY RADIAL BORES APPROXIMATELY HALF-WAY BETWEEN THE TWO INNER LANDS, SAID SLEEVE BEING FREELY MOVABLE INSIDE THE HOUSING BORE FOR A LIMITED STROKE AND INCLUDING MEANS TO PREVENT ITS FREE ROTATION ABOUT ITS AXIS, THE HOUSING HAVING FIVE PORTS COMMUNICATING WITH THE HOUSING BORE AT AXIALLY SPACED POSITIONS SO CHOSEN THAN WHEN THE SLEEVE IS IN A CENTRAL POSITION, THE INNERMOST POST IS ABOUT HALF-WAY BETWEEN THE INNER LANDS, THE TWO OUTERMOST PORTS ARE EACH HALF-WAY BETWEEN ONE OF SAID INNER LANDS AND THE ADJACENT OUTER LAND, AND THE TWO INTERMEDIATE PORTS ARE RESPECTIVELY BLANKED BY THE TWO INNER LANDS OF THE SLEEVE, THE HELICAL GROOVES BEING SO ARRANGED ON THE SPINDLE THAT FOR EACH ROTATIONAL POSITION OF THE SPINDLE THERE IS A LONGITUDINAL POSITION OF THE SLEEVE IN WHICH THE TWO RADIAL BORES HAVE EACH PART OF ITS CROSS-SECTION OPEN TO THE TWO GROOVES RESPECTIVELY AND ANOTHER PART COVERED BY PART OF THE SPINDLE ADJACENT TO THE EDGE OF SUCH GROOVE AND THAT ROTATION OF THE SPINDLE IN EITHER DIRECTION WITHOUT MOVEMENT OF THE SLIDE WILL PROGRESSIVELY INCREASE THE COVERED PART OF ONE AND DECREASE THE COVERED PART OF THE OTHER BORE, THE HOUSING HAVING A FIRST EXTERNAL CONNECTION COMMUNICATING WITH THE INNERMOST PORT, A SECOND EXTERNAL CONNECTION COMMUNICATING WITH THE TWO OUTERMOST PORTS IN PARALLEL, AND TWO SERVICE CONNECTIONS RESPECTIVELY COMMUNICATING WITH THE TWO INTERMEDIATE PORTS, THE VALVE ALSO HAVING TWO PASSAGES, EACH HAVING A METERING RESTRICTION, RESPECTIVELY CONNECTING THE PARTS OF THE HOUSING BORE AT THE TWO SIDES OF THE TWO OUTER LANDS OF THE SLEEVE THROUGHOUT THE STROKE OF THE SLEEVE.