Static pressure non-contact gas seal

A static pressure-type non-contact gas seal comprising:

• a seal casing having an inner cylinder portion, a circular inner circumferential portion concentrically surrounding said inner cylinder portion, and a ring-shaped wall portion connecting said two portions,
• a rotary seal ring fixed to a rotary shaft concentrically running through said inner cylinder portion of the seal casing,
• a stationary seal ring whose outer circumferential portion is held on the inner circumferential portion of the seal casing via a first O-ring and a second O-ring, said two O-rings arranged side by side with a specific interval therebetween, whose inner circumferential portion is held on said inner cylinder portion of the seal casing via a third O-ring, and which is slidable in the axial direction in a state where the stationary seal ring is opposite to the rotary seal ring, wherein the diameter of the second outer circumferential portion in contact with the inner circumferential portion of said second O-ring is smaller than the diameter of the first outer circumferential portion in contact with the inner circumferential portion of said first O-ring which is closer to said rotary seal ring than said second O-ring,
• springs placed between the stationary seal ring and said casing wall portion to thrust said stationary seal ring onto said rotary seal ring,
• a rotary seal end face and a stationary seal end face, both with the same inside diameter and outside diameter and each formed on the respective opposing ends of the two seal rings,
• a plurality of static pressure generating grooves formed on the seal end face of the stationary seal ring, arranged to cooperate to form a ring concentric with said end face of the stationary seal ring,
• a first closed space formed in the shape of a ring between the inner circumferential portion of the seal casing and the outer circumferential portion of said stationary seal ring and sealed by said first O-ring and said second O-ring,
• a second closed space formed in the shape of a ring between said casing wall portion and the back face portion of said stationary seal ring and sealed by said second O-ring and said third O-ring,
• a continuous seal gas supply channel formed in the seal casing and the stationary seal ring which supplies the seal gas to said static pressure generating grooves through said first closed space, said seal gas compressed to a higher pressure than the pressure in the sealed fluid region at the outer circumferential side of the two seal end faces, and
• a back pressure lead-in path connecting the sealed fluid region and the second closed space.