Seals

A gas seal for providing a seal between a pair of relatively rotatable components comprising a first seal face member mounted in rotationally fixed relationship and sealed with respect to one of said components and a second seal face member mounted in rotationally fixed relationship and sealed with respect to the other component, the first and second seal face members being urged towards one another by spring means, grooves being provided in one of said first and second seal face members to create a hydrodynamic force opposing the load applied by the spring means, when one seal face member rotates relative to the other, and a stand-still seal acting between the relatively rotatable components, the stand-still seal comprising a sealing element mounted in sealing relationship with respect to one of said components and being displaceable into sealing engagement with the other component when the components are stationary with respect to one another.