Variable back-up ring and a sealing structure having the same

A sealing structure comprising:

• a first connector body having a groove;
• a second connector body encompassing the first connector body;
• an O-ring partially received in the groove of the first connector body;
• and
• a variable back-up ring partially received in the groove of the first connector body and holding the O-ring,
• wherein the variable back-up ring is deformable in a radial direction depending on a magnitude of a fluid pressure applied between the first connector body and the second connector body,
• wherein the back-up ring includes a first half shell extending in an annular shape, a second half shell symmetrically connected to the first half shell, and an inner cavity defined by the first half shell and the second half shell, and
• wherein the inner cavity is a closed cavity.