Patent ID: 6490962
Filing Date: 2002-12-10
Classification: F15B

Abstract:
A hydraulic tool switchable between an open center mode and a closed center mode and having a work mode and a neutral mode, comprising:a cylinder defining a chamber; a piston within the chamber and operable in the neutral mode and the work mode, the piston defining a drive chamber and a retract chamber within the chamber; a valve operable to selectively supply hydraulic fluid to the drive chamber to thereby drive the piston to a first position when the tool is in the work mode, and to selectively supply the hydraulic fluid to the retract chamber to thereby move the piston to a second position when the tool is in the neutral mode; a fluid inlet and a fluid outlet in fluid communication with the valve; an oil tube in fluid communication with the valve and extending through the piston and being in communication with the retract chamber, the oil tube including opposite ends and at least one hole between said ends; and a mode selector being positionable between a first position in which the tool can operate in the open center mode in which the tool can utilize a constant volume fluid delivery source, and a second position in which the tool can operate in the closed center mode in which the tool can utilize a constant pressure fluid delivery source; wherein, in the open center work mode the valve is configured to supply the hydraulic fluid through the oil tube to the drive chamber to drive the piston to the first position, and wherein when the tool is moved to the neutral mode, the valve is configured to supply the hydraulic fluid through the oil tube to the retract chamber such that movement of the piston to the second position can allow communication between the inlet and outlet through the at least one hole in the oil tube.