System for backup rod seal for hydraulic cylinder

A method of providing back-up rod sealing protection in a hydraulic cylinder when its primary seal becomes worn, the hydraulic cylinder having a cylinder tube and a cylinder head defining a working chamber and a piston disposed for linear reciprocable movement within the working chamber and connected to a piston rod projecting outwardly through the cylinder head, wherein the method comprises:

• providing a primary seal acting between the cylinder head and the piston rod;
• providing a back-up seal acting between the cylinder head and the piston rod;
• providing a bypass channel with a bypass valve therein fluidically connecting the working chamber with a chamber in the cylinder head between the back-up seal and the primary seal,
• placing the primary seal in service when the cylinder is first put into operation by opening the bypass valve thereby allowing the hydraulic fluid to flow 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;
• and
• placing the back-up seal in service when the primary seal becomes worn by closing the bypass valve such that the back-up seal controls leakage of hydraulic fluid around the piston rod.

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 back-up seal acting between the cylinder head and the piston rod;
• and
• means for placing the primary seal in service when the cylinder is first put into operation 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, said means also configured to selectively place the back-up seal in service when the primary seal becomes worn such that the back-up seal controls leakage of hydraulic fluid around the piston rod.