Unloading relief valve

Claim 1

AN UNLOADING RELIEF VALVE DEFINING A VALVE CHAMBER HAVING INLET AND OUTLET PASSAGES COMMUNICATING THEREWITH, A SPOOL VALVE MEMBER IN SAID CHAMBER HAVING FIRST AND SECOND BOSSES CONNECTED BY A STEM, SAID INLET PASSAGE COMMUNICATING WITH SAID VALVE CHAMBER BETWEEN THE INNER ENDS OF SAID BOSSES, MEANS YIELDABLY URGING SAID SPOOL MEMBER TO A CLOSED POSITION IN WHICH SAID SECOND BOSS OVERLIES SAID OUTLET TO BLOCK FLOW THERETO, A PLUNGER CONNECTED TO THE OUTER END OF SAID FIRST BOSS, MEANS SLIDABLY ENGAGING SAID PLUNGER TO SEPARATE THE AREA AT THE END OF SAID PLUNGER FROM THE REMAINING AREA ON SAID OUTER END OF SAID FIRST BOSS, A FIRST PASSAGE MEANS FOR APPLYING FLUID PRESSURE FROM SAID INLET PASSAGE TO THE AREA ON THE END OF SAID PLUNGER, A FLOW RESTRICTING DEVICE IN SAID OUTLET PASSAGE FOR PRODUCING A PRESSURE DROP THEREACROSS CORRELATIVE WITH THE RATE OF FLOW OF FLUID FROM SAID INLET TO SAID OUTLET, A SECOND PASSAGE MEANS COMMUNICATING WITH SAID OUTLET PASSAGE UPSTREAM OF SAID RESTRICTING DEVICE FOR APPLYING THE PRESSURE THEREAT TO THE REMAINING AREA AT SAID OUTER END OF SAID FIRST BOSS, AND A THIRD PASSAGE MEANS COMMUNICATING WITH THE OUTLET PASSAGE DOWNSTREAM OF SAID RESTRICTING DEVICE FOR APPLYING THE PRESSURE THEREAT TO THE OUTER END OF SAID SECOND BOSS.