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Pressure control mechanism for a grapple skidder

  • US 4,431,365 A
  • Filed: 01/27/1981
  • Issued: 02/14/1984
  • Est. Priority Date: 07/13/1977
  • Status: Expired due to Fees
First Claim
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1. A hydraulic control system for a self propelled log grapple skidder having a boom arm operated by a first double acting hydraulic cylinder, a grapple operated by a second double acting hydraulic cylinder, and a hydraulic pump for operating both hydraulic cylinders, the system comprisinga first three position valve having neutral, extend and retract positions,first conduit means interconnecting said first valve with said first hydraulic cylinder for selectively operating the first hydraulic cylinder independently of said second hydraulic cylinder,a second three position valve having neutral, extend and retract positions,second conduit means interconnecting said second valve with said second hydraulic cylinder for selectively operating the second hydraulic cylinder independently of said first hydraulic cylinder,first interconnecting means between a rod end of said first cylinder and a base end of said second cylinder, operable when said first and second valves are in neutral, for selectively causing said second cylinder to maintain a hydraulic pressure in the base end of the second cylinder not less than the pressure in the rod end of the first cylinder, andsecond interconnecting means which is open at all times comprising a hydraulic conduit joining the rod end of said second cylinder and the base end of first boom cylinder.

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