Radial separation seal

A seal ring for a radial separation seal, the seal ring comprising:

• a first ring segment comprising a male portion;
• and
• a second ring segment comprising a female portion, wherein the female portion is configured to engage the male portion in the manner of a tongue and groove joint, the joint having:
• an inner interface at which the first ring segment abuts the second ring segment, the inner interface comprising two inner sealing surfaces;
• and
• an outer interface at which the first ring segment abuts the second ring segment the outer interface comprising two outer sealing surfaces;
• wherein the outer interface is radially outward from the inner interface, wherein the first and second ring segments are moveable relative to one another so that they can be in either a contracted or expanded position, wherein in the contracted position the inner sealing surfaces are in contact and the outer sealing surfaces are not and wherein when a fluid flow is provided to the inner interface, fluid pressure from the fluid flow moves the first and second ring segments into the expanded position by pushing the inner sealing surfaces of the inner interface apart to seal the outer sealing surfaces of the outer interface together.