Hydraulic system and valve arrangement therein

Claim 1

A HYDRAULIC SYSTEM FOR CONTROLLING THE HEIGHT OF A CUTTING HEAD ON A VEHICLE HAVING GROUND-ENGAGING FEELER MEANS, SAID SYSTEM COMPRISING: A RESERVOIR FOR HYDRAULIC LIQUID; A PUMP CONNECTED TO SAID RESERVOIR TO PUMP LIQUID THEREFROM; A HYDRAULIC MOTOR FOR RAISING AND LOWERING SAID CUTTING HEAD; AN OPEN-CENTER VALVE HAVING AN INLET PORT CONNECTED TO THE PUMP OUTLET, A MOTOR PORT CONNECTED TO SAID MOTOR, A RETURN PORT CONNECTED TO THE RESERVOIR, AN ADDITIONAL PORT, AND A RECIPROCABLE VALVE SPOOL POSITIONED BETWEEN SAID INLET, RETURN, MOTOR AND ADDITIONAL PORTS AND CONTROLLING THE RESPECTIVE LIQUID FLOWS BETWEEN SAID PORTS, SAID VALVE SPOOL HAVING A NEUTRAL POSITION IN WHICH IT CONNECTS SAID INLET PORT TO SAID RETURN PORT, SAID VALVE SPOOL HAVING A "RAISE" POSITION AT ONE SIDE OF SAID NEUTRAL POSITION IN WHICH IT CONNECTS SAID INLET PORT TO SAID MOTOR PORT AND BLOCKS SAID RETURN PORT FROM BOTH SAID INLET PORT AND SAID MOTOR PORT AND CONNECTS SAID ADDITIONAL PORT TO SAID RETURN PORT, SAID VALVE SPOOL HAVING A "LOWER" POSITION AT THE OPPOSITE SIDE OF SAID NEUTRAL POSITION IN WHICH IT CONNECTS SAID MOTOR PORT TO SAID RETURN PORT AND BLOCKS SAID INLET PORT FROM BOTH SAID RETURN AND MOTOR PORTS AND CONNECTS SAID INLET PORT TO SAID ADDITIONAL PORT, AND SPRING MEANS IN SAID VALVE BIASING SAID VALVE SPOOL TO ITS "LOWER" POSITION; A NORMALLY-CLOSED COUNTERBALANCE VALVE CONNECTED BETWEEN SAID MOTOR PORT AND THE HYDRAULIC MOTOR AND PREVENTING RETURN FLOW FROM THE MOTOR IN SAID NEUTRAL POSITION OF SAID RECIPROCABLE VALVE MEANS, SAID COUNTERBALANCE VALVE BEING RESPONSIVE TO LIQUID PRESSURE AT SAID MOTOR PORT TO OPEN IN SAID "RAISE" POSITION OF SAID RECIPROCABLE VALVE MEANS, AND A MOVABLE PRESSURE-RESPONSIVE MEMBER CONNECTED TO SAID ADDITIONAL PORT AND OPERABLE BY LIQUID PRESSURE THEREAT IN SAID "LOWER" POSITION OF SAID RECIPROCABLE VALVE MEANS TO HOLD SAID COUNTERBALANCE VALVE OPEN FOR RETURN FLOW FROM SAID MOTOR TO SAID MOTOR PORT AND THENCE TO SAID RETURN PORT AT A RATE PROPORTIONAL TO THE LIQUID PRESSURE AT SAID ADDITIONAL PORT ACTING ON SAID MOVABLE PRESSURE-RESPONSIVE MEMBER; A MOVABLE RIGID MODULATING MEMBER OPERATED BY SAID GROUND-ENGAGING FEELER MEANS AND ENGAGING SAID RECIPROCABLE VALVE MEANS IN OPPOSITION TO SAID SPRING MEANS, SAID MODULATING MEMBER BEING MOVABLE INWARDLY AGAINST THE URGING OF SAID SPRING MEANS TO POSITION SAID VALVE SPOOL IN ITS "RAISE" POSITION AND BEING MOVABLE OUTWARDLY TO PERMIT SAID SPRING MEANS TO POSITION SAID VALVE SPOOL IN ITS "LOWER" POSITION; AND A MANUAL CONTROL MEMBER SELECTIVELY ENGAGEABLE WITH SAID VALVE SPOOL IN OPPOSITION TO SAID SPRING MEANS TO POSITION SAID VALVE SPOOL IN ITS "RAISE" POSITION INDEPENDENT OF THE POSITION OF SAID MODULATING MEMBER.