Hydrostatic transmission

Claim 1

IN A HYDROSTATIC TRANSMISSION INCLUDING A FLUID PUMP HYDRAULICALLY CONNECTED TO A FLUID MOTOR WHEREIN THE PUMP IS ADAPTED TO BE CONNECTED TO A POWER SOURCE AND THE MOTOR IS ADAPTED TO BE CONNECTED TO A DRIVE A LOAD, AT LEAST TWO FLUID PASSAGEWAYS INTERCONNECTING SAID PUMP AND MOTOR, ONE OF SAID PASSAGEWAYS BEING A HIGH PRESSURE PASSAGEWAY AND THE OTHER A LOW PRESSURE PASSAGEWAY, A PRESSURE RELIEF VALVE OPERATIVE TO PREVENT PRESSURES BEYOND A PREDETERMINED MAXIMUM FROM BEING DEVELOPED IN SAID PASSAGEWAYS COMPRISING A BODY HAVING A BORE THEREIN AND A VALVE SPOOL SLIDABLE WITHIN SAID BORE, A PAIR OF FLUID PASSAGES EACH COMMUNICATING WITH ONE OF SAID PASSAGEWAYS AND WITH SAID BORE, BIASING MEANS IN SAID BORE URGING SAID VALVE SPOOL TO A POSITION IN WHICH FLUID FLOW BETWEEN SAID PAIR OF PASSAGES IS BLOCKED, A FLUID PASSAGE CONNECTED TO SAID TWO PASSAGEWAYS TO SUPPLY FLUID PRESSURE FROM THE HIGH PRESSURE PASSAGEWAY TO BOTH ENDS OF SAID BORE, MEANS ADAPTED TO EXHAUST FLUID FROM SAID ONE END OF SAID BORE WHEN A PREDETERMINED FLUID PRESSURE IS REACHED WITHIN SAID ONE END, MEANS TO RESTRICT FLUID FLOW FROM SAID FLUID PASSAGE INTO ONE END OF SAID BORE, SAID FLOW RESTRICTING MEANS PRODUCING A PRESSURE UNBALANCE BETWEEN THE ENDS OF SAID BORE WHEN FLUID IS EXHAUSTED FROM SAID ONE END OF THE BORE AND THEREBY MOVING SAID VALVE SPOOL TO INTERCONNECT SAID PAIR OF FLUID PASSAGES AND REGULATE THE FLUID PRESSURE DEVELOPED TO A PREDETERMINED MAXIMUM, SAID FLUID EXHAUSTING MEANS AND SAID FLOW RESTRICTING MEANS PROVIDING FLUID PRESSURE REGULATION WITH SUBSTANTIALLY LESS FLUID FLOW THAN EXISTING IN SAID TWO PASSAGEWAYS.