Importance

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Abstract

A hydraulic control system for excavators includes a variable displacement pump for producing a variable volume of pressurized working fluid, a hydraulic swing motor rotatably driven by the working fluid and a flow control valve operable to control flow of the working fluid with respect to the swing motor. The first flow control valve comprises a valve body and a valve spool slidably fitted into the valve body for selective shifting movement between a first operative position, a second operative position and a neutral position. The valve body has first and second control pressure chambers arranged at opposite ends thereof in an opposing relationship with each other, the first control pressure chamber adapted to receive a part of the working fluid headed for the swing motor to urge the valve spool toward the second operative position in response to the shifting movement of the valve spool into the first operative position, the second control pressure chamber adapted to receive a part of the working fluid headed for the swing motor to bias the valve spool toward the first operative position in response to the shifting movement of the valve spool into the second operative position.

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First Claim