Hydraulic system

Claim 1

A HYDRAULIC SYSTEM FOR OPERATING A FLUID MOTOR FROM A PUMP COMPRISING: A CLOSED-CENTER SPOOL VALVE COMPRISING A VALVE BODY HAVING A BORE THEREIN AND A PLURALITY OF RECESSES INTERSECTING SAID BORE AT SPACED LOCATIONS THEREALONG AND INCLUDING PUMP RECESS MEANS FOR CONNECTING TO THE PUMP AND RETURN RECESS MEANS FOR CONNECTION TO A LOW PRESSURE RETURN LINE AND ADDITIONAL RECESSES, AND A SPOOL SLIDABLY RECEIVED IN SAID BORE AND HAVING A PLURALITY OF LONGITUDINALLY SPACED LANDS THEREON FOR SEALING ENGAGEMENT WITH THE BORE AND HAVING REDUCED DIAMETER PORTIONS BETWEEN ITS LANDS; A FIRST NORMALLY-CLOSED CHECK VALVE CONNECTED TO ONE OF SAID ADDITIONAL RECESSES IN THE SPOOL VALVE BODY AND HAVING A PORT FOR CONNECTION TO ONE SIDE OF THE FLUID MOTOR, A FIRST PRESSURE RESPONSIVE MEMBER CONNECTED TO ANOTHER OF SAID ADDITIONAL RECESSES IN THE SPOOL VALVE BODY AND MOVABLE IN RESPONSE TO FLUID PRESSURE THEREAT TO OPEN SAID CHECK VALVE; A SECOND NORMALLY-CLOSED CHECK VALVE CONNECTED TO ANOTHER OF SAID ADDITIONAL RECESSES IN THE SPOOL VALVE BODY AND HAVING A PORT FOR CONNECTION TO THE OPPOSITE SIDE OF THE FLUID MOTOR, A SECOND PRESSURE RESPONSIVE MEMBER CONNECTED TO ANOTHER OF SAID ADDITIONAL RECESSES IN THE SPOOL VALVE BODY AND MOVABLE IN RESPONSE TO FLUID PRESSURE THEREAT TO OPEN SAID SECOND CHECK VALVE; SAID SPOOL IN A FIRST POSITION THEREOF ALONG THE BORE IN THE SPOOL VALVE BODY BLOCKING SAID PUMP RECESS MEANS FROM BOTH CHECK VALVES AND CONNECTING THE RESPECTIVE PRESSURE RESPONSIVE MEMBERS IN BOTH CHECK VALVES TO THE LOW PRESSURE RETURN THROUGH THE SPOOL VALVE BODY TO MAINTAIN BOTH CHECK VALVES CLOSED TO BLOCK THE FLOW OF HYDRAULIC LIQUID FROM EITHER SIDE OF THE FLUID MOTOR;