Turbo-type fluid machine and a stepped seal apparatus to be used therein

1. A turbo-type fluid machine comprising a rotating shaft arranged in a pump casing, an impeller mounted on the rotating shaft, and a mouth ring part provided between a shroud of the impeller and the pump casing and having a seal function, and

wherein the mouth ring part comprises an impeller ring on a side of the shroud of the impeller and a casing ring provided on a side of a non-rotating body wall surface of the casing,

the impeller ring is structured to have a stepped portion that is in the form of a staircase with at least two steps to be small in diameter toward a suction side of the impeller and large in diameter toward an outlet of the impeller, and

the casing ring is labyrinth-shaped to have a projection and a recess, a narrow clearance part having a narrow radial clearance is formed between the projection and the impeller ring, and a flow passage spatial portion defining an enlarged portion of the narrow radial clearance is formed by the recess and the stepped portion of the impeller ring.

2. A turbo-type fluid machine according to claim 1 , wherein axial positions of a radial wall portion of the stepped portion of the impeller ring and a radial wall portion of the labyrinth-shaped recess on the side of the non-rotating body coincide with or substantially coincide with each other.

3. A turbo-type fluid machine according to claim 1 , wherein the flow passage spatial portion formed by the stepped portion of the impeller ring and the labyrinth-shaped recess on the side of the non-rotating body is made substantially rectangular-shaped, and a radial position of the narrow clearance part with the narrow radial clearance is radially outward from a radially central position of the flow passage spatial portion, which is formed by the stepped portion and the labyrinth-shaped recess and provided downstream of the narrow clearance part.

4. A turbo-type fluid machine according to claim 3 , wherein a radial position of the narrow clearance part is radially outward from a bottom surface of the flow passage spatial portion, which is formed by the stepped portion and the labyrinth-shaped recess, to be in the range of a height of ½ to ¾ as high as the flow passage spatial portion.

5. A turbo-type fluid machine comprising a rotating shaft arranged in a casing, an impeller mounted on the rotating shaft, and a mouth ring part provided between a shroud of the impeller and the casing and having a seal function, and

wherein the mouth ring part comprises an impeller ring on a side of the shroud of the impeller and a casing ring provided on a side of a non-rotating body wall surface of the casing,

the impeller ring is structured to have a stepped portion with at least three steps to be small in diameter toward a suction side of the impeller and large in diameter toward an outlet of the impeller, and

the casing ring includes a labyrinth-shaped projection and a labyrinth-shaped recess, a narrow clearance part is formed between the labyrinth-shaped projection and the impeller ring, a flow passage spatial portion defining an enlarged portion of a radial clearance is formed by the labyrinth-shaped recess and the stepped portion of the impeller ring, so that a secondary flow (D) directed radially outwardly of the narrow clearance part from radially inwardly of the narrow clearance part is generated.

6. A turbo-type fluid machine according to claim 1 , wherein a material of the casing ring is a thermoplastic resin.

7. A turbo-type fluid machine according to claim 1 , wherein a plurality of shallower labyrinth grooves than a depth of the recess are formed on an inner wall surface of the projection of the casing ring that defines the narrow clearance part.

8. A stepped seal apparatus comprising a narrow staircase-shaped clearance formed between a rotating body and a stationary body of a turbo-type fluid machine to provide for sealing therebetween, and

wherein a seal surface on a side of the rotating body is structured to be small in diameter on a suction side and large in diameter on a discharge side and to comprise a stepped portion of at least three stages, and

a seal surface of the stationary body is structured to include a labyrinth-shaped projection and a labyrinth-shaped recess, a narrow clearance part is formed between the labyrinth-shaped projection and the seal surface on the side of the rotating body, a flow passage spatial portion defining an enlarged portion of a radial clearance is formed by the labyrinth-shaped recess and the stepped portion of the seal surface on the side of the rotating body so that and a secondary flow directed radially outwardly of the narrow clearance part from radially inwardly of the narrow clearance part is generated in the flow passage spatial portion.

9. A turbo-type fluid machine according to claim 8 , wherein a material of a member that defines the seal surface on the side of the stationary body is a thermoplastic resin, and a radial position of the narrow clearance part is radially outward from a bottom surface of the flow passage spatial portion formed by the stepped portion and the labyrinth-shaped recess to be in the range of a height of ½ to ¾ as high as the flow passage spatial portion.