Carbon seal O-ring cavity sizing

A carbon seal assembly comprising:

• a carbon seal element disposed about a central axis and extending between a first end and a second end, the carbon seal element including an inner step surface, an outer step surface, an axial distance H1 from the first end to the inner step surface, an axial distance H2 from the first end to the outer step surface and an axial distance H3 from the first end to the second end, and H1 is greater than or equal to 35% of the axial distance H3 and H2 is greater than or equal to 60% of the axial distance H3.

A method for controlling leakage in a carbon seal assembly, the method comprising:

• providing a carbon seal element disposed about a central axis and extending between a first end and a second end, the carbon seal element including an inner step surface at an axial distance H1 with regard to the first end and an o-ring adjacent to the inner step surface, the o-ring including a cross-section diameter D2;
• and
• limiting leakage of a fluid by the o-ring by establishing a ratio H1/D2 that is between 1.60-1.73.