Hydraulic position lock

Claim 1

A HYDRAULIC POSITION LOCK COMPRISING AN ELONGATED CYLINDER HAVING END WALLS, A PISTON MOUNTED FOR RECIPROCAL MOVEMENT WITHIN SAID CYLINDER AND IN SLIDABLE SEALING ENGAGEMENT THEREWITH, SAID PISTON HYDRAULICALLY DIVIDING SAID CYLINDER INTO TWO CLOSED COMPARTMENTS, TWO PISTON RODS INTEGRAL WITH SAID PISTON, EACH ROD EXTENDING THROUGH AN ADJACENT CYLINDER END WALL IN SLIDABLE SEALING ENGAGEMENT THEREWITH, AT LEAST ONE OF SAID RODS BEING TUBULAR, A PASSAGEWAY THROUGH SAID PISTON COMMUNICATING BETWEEN SAID COMPARTMENTS, SAID PASSAGEWAY INCLUDING A FIRST PORTION, A SECOND PORTION HAVING A CROSS SECTIONAL AREA SMALLER THAN THE CROSS SECTIONAL AREA OF THE FIRST PORTION, AND A SHUNT PORTION HAVING A CROSS SECTIONAL AREA LARGER THAN THE CROSS SECTIONAL AREA OF THE SECOND PORTION, SAID SHUNT PORTION BRIDGING THE SECOND PORTION, AN INCOMPRESSIBLE LIQUID FILLING SAID COMPARTMENTS AND SAID PASSAGEWAY, A MANUALLY CONTROLLABLE LOCK VALVE ASSOCIATED WITH THE PASSAGEWAY, SAID VALVE HAVING A MEMBER MOUNTED FOR MOVEMENT BETWEEN A CLOSED POSITION BLOCKING SAID PASSAGEWAY PREVENTING LIQUID FLOW AND IMMOBILIZING THE PISTON, AND AN OPEN POSITION UNBLOCKING SAID PASSAGEWAY PERMITTING LIQUID FLOW AND ALLOWING THE PISTON TO EXPERIENCE MOTION, SAID LOCK VALVE HAVING A FACE MOUNTED AND ARRANGED OPPOSE HYDRAULIC PRESSURE EXERTED BY ONLY ONE COMPARTMENT, A SPRING BIASING SAID LOCK VALVE TO ITS CLOSED POSITON SO THAT SAID PASSAGEWAY IS NORMALLY BLOCKED SAID SPRING BEING MOUNTED TO OPPOSE LOCK VALVE MOVEMENT CAUSED BY PRESSRUE ON THE VALVE FACE, AN ACTUATING MEMBER DISPOSED WITHIN SAID TUBULAR PISTON ROD TO ACT AGAINST SAID BIASING SPRING, SAID MEMBER BEING MOUNTED TO SELECTIVELY MOVE SAID LOCK VALVE TO ITS OPEN POSITION, AND A CHECK VALVE ASSOCIATED WITH THE SHUNT PORTION OF SAID PASSAGEWAY AND MOUNTED FOR MOVEMENT BETWEEN A CLOSED POSITION BLOCKING SAID SHUNT PORTION AND AN OPEN POSITION UNBLOCKING THE SHUNT PORTION, SAID CHECK VALVE BEING RESPONSVE OT UNIDIRECTIONAL LIQUID FLOW, SO THAT WHEN THE LOCK VALVE IS IN ITS OPEN POSITION, LIQUID FLOW IN ONE DIRECTION WILL OPEN THE CHECK VALVE AND FLOW THROUGH THE PASSAGEWAY INCLUDING THE SECOND PORTION AND THE SHUNT PORTION ALLOWING THE PISTON TO EXPERIENCE COMPARATIVELY FREE MOVEMENT, AND LIQUID FLOW IN THE OPPOSITE DIRECTION WILL CLOSE THE CHECK VALVE AND FLOW THROUGH THE PASSAGEWAY INCLUDING THE SECOND PORTION BUT NOT THE SHUNT PORTION ALLOWING THE PISTON TO EXPERIENCE COMPARATIVELY RESTRAINED MOVEMENT.