Patent ID: 7607383
Filing Date: 2009-10-27
Classification: F15B,F16J

Abstract:
1. A hydraulic cylinder having a cylinder tube and a cylinder head defining a working chamber, a piston being disposed for linear reciprocable movement within the working chamber and connected to a piston rod projecting outwardly through the cylinder head, and a rod sealing system capable of being adjusted so as to place back-up rod sealing protection in service when its primary seal becomes worn, wherein the rod sealing system comprises: a primary seal acting between the cylinder head and the piston rod; a secondary seal acting between the cylinder head and the piston rod; a back-up seal acting between the cylinder head and the piston rod; and a bypass valve located in a bypass channel in the cylinder head, said bypass channel fluidically connecting the working chamber with a chamber in the cylinder head between the back-up seal and the primary seal, wherein flow of hydraulic fluid through the bypass channel is selectively allowed or prevented with the bypass valve; wherein the bypass valve is configured such that it places the primary seal in service when the cylinder is first put into operation when said bypass valve is placed in its open position, thereby allowing the flow of hydraulic fluid through the bypass channel, so that the chamber in the cylinder head is maintained at substantially the same pressure as a piston rod portion of the working chamber such that the primary seal acts as the sealing member to control leakage of hydraulic fluid around the piston rod, and pressurized hydraulic fluid at substantially identical pressure is present on both sides of the back-up seal such that the back-up seal is not in service to control leakage of hydraulic fluid around the piston rod, and the bypass valve is further configured such that it places the back-up seal in service when said bypass valve is placed in its closed position, such that the back-up seal controls leakage of hydraulic fluid around the piston rod.