Importance

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Abstract

A pilot-operated pressure relief valve is provided for a hydrostatic transmission. The override valve is in the closed circuit loop, which includes a pair of multi-function valves and a displacement control valve. The pressure override valve includes a spool slideably mounted within a body so as to be responsive to a pressure differential created by pilot flow through the override valve. The spool is biased to a normal position which provides fluid communication between a pressure charge source and the displacement control valve. As the pressure differential in the override valve increases, the spool shifts so as to close such communication from the charge source to the control valve, thereby defeating the pressure signal from the control valve to the servos of the hydrostatic transmission pump. As the pressure differential increases further, the spool of the override valve shifts further so as to provide communication between the control valve and tank, thereby allowing the fluid in the high side servo to flow backwards through the control valve to tank. The close circuit loop includes a plurality of plugs which are selectively opened and closed to provide different loop configurations.

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First Claim