Pressure controllable packing

In an elastic packing installed at a packing groove formed at an edge of a cover so as to isolate an inner space defined by a vessel and the cover from an outer space, a pressure controllable packing comprising:

• first and second rims extending in opposite axial direction pushed by a pressure of the inner space in directions tending to adhere closely to a surface of the packing groove and an edge surface of the vessel;
• a support part installed at a circumference end of the packing groove so as to be contacted with the circumference end and connecting the first and second rims to each other;
• and
• at least one long groove formed at a portion of the support part at which the first and second rims are connected to the support part and having an open end toward the first rim;
• at least one second long groove formed at portion of the support part at which the first and second rims are connected to the support part and having an open end toward the second rim,
• wherein the first or second rim at a portion where the long groove is formed is pushed in a circumferential direction so as to generate a distorted portion if a pressure of the inner space increases to exceed a predetermined value, and wherein a gap is generated from the distorted portion between surfaces of the first and second rim and the long groove or the edge surface of the vessel so as to reduce the pressure of the inner surface through the gap.