A packing stack comprising: a plurality of V-shaped packing rings (34A, 34B) arranged in a stack, wherein each of the V-shaped packing rings has an annular convex front rib portion and an annular concave groove portion; wherein the annular convex front rib portion includes an annular front apex surface, an annular outer front angled surface, an annular inner front angled surface, an annular outer side surface, and an annular inner side surface; wherein the annular concave groove portion includes an annular trench surface, an annular outer rear angled surface, an annular inner rear angled surface, an annular outer rear rim surface, and an annular inner rear rim surface; wherein the annular front apex surface is wider than the annular trench surface; wherein the annular outer front angled surface extends between the annular front apex surface and the annular outer side surface; wherein the annular inner front angled surface extends between the annular front apex surface and the annular inner side surface; wherein the annular outer rear angled surface extends between the annular trench surface and the annular outer rear rim surface; wherein the annular inner rear angled surface extends between the annular trench surface and the annular inner rear rim surface; wherein the annular outer rear rim surface extends between the annular outer rear angled surface and the annular outer side surface; wherein the annular inner rear rim surface extends between the annular inner rear angled surface and the annular inner side surface; wherein the annular outer front angled surface and the annular inner front angled surface form a first angle; wherein the annular outer rear angled surface and the annular inner rear angled surface form a second angle; characterized in that the second angle is greater than the first angle; and wherein gaps are located in the packing stack between adjacent annular outer front angled and outer rear angled surfaces (110, 122), and between adjacent annular inner front angled and inner rear angled surfaces (112, 124). a plurality of V-shaped packing rings (34A, 34B) arranged in a stack, wherein each of the V-shaped packing rings has an annular convex front rib portion and an annular concave groove portion; wherein the annular convex front rib portion includes an annular front apex surface, an annular outer front angled surface, an annular inner front angled surface, an annular outer side surface, and an annular inner side surface; wherein the annular concave groove portion includes an annular trench surface, an annular outer rear angled surface, an annular inner rear angled surface, an annular outer rear rim surface, and an annular inner rear rim surface; wherein the annular front apex surface is wider than the annular trench surface; wherein the annular outer front angled surface extends between the annular front apex surface and the annular outer side surface; wherein the annular inner front angled surface extends between the annular front apex surface and the annular inner side surface; wherein the annular outer rear angled surface extends between the annular trench surface and the annular outer rear rim surface; wherein the annular inner rear angled surface extends between the annular trench surface and the annular inner rear rim surface; wherein the annular outer rear rim surface extends between the annular outer rear angled surface and the annular outer side surface; wherein the annular inner rear rim surface extends between the annular inner rear angled surface and the annular inner side surface; wherein the annular outer front angled surface and the annular inner front angled surface form a first angle; wherein the annular outer rear angled surface and the annular inner rear angled surface form a second angle; characterized in that the second angle is greater than the first angle; and wherein gaps are located in the packing stack between adjacent annular outer front angled and outer rear angled surfaces (110, 122), and between adjacent annular inner front angled and inner rear angled surfaces (112, 124).