Sealing device

1. A sealing device comprising:

an impeller configured to rotate;

a casing configured to contact the impeller and comprising a groove portion on a surface facing the impeller;

a floating ring configured to float between the casing and the impeller, the floating ring comprising a protruding portion configured to be inserted into the groove portion;

a centering ring provided inside the groove portion and provided between the casing and the protruding portions; and

a retaining ring coupled to the casing, the retaining ring contacting a surface of the protruding portion inserted into the groove portion,

wherein the retaining ring is provided in an opposite side to a surface of the floating ring that contacts the casing, and the retaining ring is provided to cover the groove portion in order that the centering ring remains inside the groove portion.

2. The sealing device of claim 1 , wherein the centering ring is configured to be elastically deformed in response to the centering ring being pressed by the floating ring against the casing.

3. The sealing device of claim 2 , wherein the centering ring comprises an elastic material.

4. The sealing device of claim 1 , wherein the centering ring comprises a ring having a “C” or “O”-shaped cross-section.

5. The sealing device of claim 1 ,

wherein the impeller comprises a step surface on a surface facing the floating ring, and

wherein the floating ring comprises a step portion having a corresponding shape of the step surface on a surface facing the impeller.

6. The sealing device of claim 1 , wherein the protruding portion protrudes from a base portion of the floating ring, and

wherein the base portion is configured to contact the impeller.

7. The sealing device of claim 1 , wherein the centering ring is configured to contact the casing and the floating ring.