Pressure activated non-contact seals and seal assemblies

A pressure activated non-contact seal for sealing against a rotating cylindrical surface between a high-pressure region and a low-pressure region, comprising:

• a seal member carrier spaced radially from the rotating cylindrical surface and defining a seal member chamber in fluid communication with the high-pressure region;
• a seal member supported by the seal member carrier so as to be moveable in a radial direction of the rotating cylindrical surface, and comprising non-contact seal surfaces adjacent to the rotating cylindrical surface;
• and
• a secondary seal mounted between a surface of the seal member facing the seal member carrier and an opposed surface of the seal member chamber to provide a pressure barrier around the seal member between the high-pressure region and the low-pressure region;
• wherein:
• the seal member comprises side walls extending in the radial direction towards the rotating cylindrical surface and defining a seal cavity, the ends of the side walls adjacent to the rotating cylindrical surface defining non-contact seal surfaces;
• and
• the seal member further comprises a bleed port extending between the seal cavity and the seal member chamber on the high-pressure side of the secondary seal such that in use, high pressure in the seal member chamber urges the seal member towards the rotating cylindrical surface until balanced by the pressure in the seal cavity to maintain the non-contact seal surfaces in a non-contact sealing relationship with the rotating cylindrical surface.