Seal

A sealing device for making a seal against an annular surface, the device comprising at least one flexible seal ring having a relaxed position in which the seal ring is out of contact with the surface and an active position in which the seal ring is in sealing contact with the surface, an operating member movable relative to the seal ring in a direction substantially parallel to the annular surface to produce a substantially radial movement of the ring into the active position, and a plurality of elongate, substantially parallel shape-memory material actuators arranged around the annular surface so that a change of shape of the actuators produces the movement of the operating member which moves the seal ring into the active position wherein the actuators are in the form of rods, the axes of which extend substantially parallel to the surface and the actuators each have one threaded end and one end with a head, the threaded ends are screwed into threaded sockets in the main body and the heads engage the operating member.