Noncontacting face seal

Abstract: A noncontacting face seal has a stationary sealing ring (4) and a rotating sealing ring (3) with opposed radially extending sealing surfaces (3S,4S) for restricting a fluid flow from a high pressure fluid side (H) to a low pressure fluid side (L). The rotating sealing ring (3) is brought out of contact with the stationary sealing ring (4) under hydrostatic force from fluid. The noncontacting face seal comprises spiral grooves (33) formed in one of the sealing surfaces (3S,4S) and extending from a low pressure fluid side (L) to a high pressure fluid side (H) in a radial direction so as to pump fluid in the low pressure fluid side (L) towards the high pressure fluid side (H), and a spaced portion (31,38) formed in one of the sealing surfaces (3S,4S) and extending inwardly from one circumference of the sealing surface at the high pressure fluid side (H) so as to introduce fluid in the high pressure fluid side (H) between the sealing surfaces (3S,4S).

Description: BACKGROUND OF THE INVENTION The present invention relates to a noncontacting face seal, and more particularly to a noncontacting face seal in which an end face of a rotating sealing ring rotatable with a rotating shaft and an end face of a stationary sealing ring facing the rotating sealing ring form sealing surfaces for restricting a fluid flow from a high pressure side to a low pressure side. A noncontacting end face seal (hereinafter referred to as end face seal) is used for sealing the space between a rotating shaft and a housing thereof. The end face seal is incorporated in, for example, gas turbines or compressors which handle high pressure. In general, there are two types of noncontacting end face seals, one of which is a hydrostatic end face seal using the pressure of sealing fluid, the other of which is a hydrodynamic end face seal with shape causing hydrodynamic action such as spiral grooves. Next, the conventional hydrostatic end face seal will be described below with reference to Figs. 12 and 13. The end face seal comprises two annular sealing rings facing with each other, one of which is a rotating sealing ring 3, the other of which is a stationary sealing ring 4. A rotating shaft 1 accommodated in a housing 9 is provided with a sleeve 2. The sleeve 2 is connected to the rotating sealing ring 3 through a pin. The stationary sealing ring 4 is pressed against the rotating sealing ring 3 by urging force of springs 10 interposed between a sealing ring retainer 5 and a spring retainer 6. In the end face seal, the radially outer region of the rotating sealing ring 3 is located at high pressure fluid side H and the radially inner region thereof at low pressure fluid side L. The rotating sealing ring 3 is provided with an outwardly tapered surface 31 which makes the gap between the rotating sealing ring 3 and the stationary sealing ring 4 wider gradually. That is, the tapered surface 31 provides the necessary wedge-shaped space between the rotating sealing ring 3 and the stationary sealing ring 4 at the radially outer regions thereof for introducing fluid between two sealing rings. The rotating sealing ring 3 is further provided with a flat surface 32 inside the tapered surface 31. In the end face seal of this type, when fluid enters into the wedge-shaped space between the rotating sealing ring 3 and the stationary sealing ring 4, the sealing surfaces become noncontact by hydrostatic forces from fluid pressure. The distance e between the outer edge of the tapered surface 31 of the rotating sealing ring 3 and the sealing surface of the stationary sealing ring 4, the inner diameter 2r t of the tapered surface 31, the inside diameter 2r 1 of the sealing surface and the outside diameter 2r 2 of the sealing surface are properly arranged so that the gap of the sealing surfaces become small to the utmost extent and the stiffness of fluid film formed on the sealing surfaces enhances. In the conventional end face seal as shown in Figs. 12 and 13, in order to reduce leakage of fluid from the sealing surfaces, it is necessary to make the gap of the sealing surfaces small. However, there is a limit to reduction of the gap. Therefore, in the end face seal of this type, it is difficult to reduce the leakage of fluid to a certain extent or less. On the other hand, another type of end face seal with spiral grooves is disclosed in U.S. Pat. No. 3,499,653. In U.S. Pat. No. 3,499,653 the end face seal comprises a rotating sealing ring and a stationary sealing ring as well as the end face seal in Figs. 11 and 12. One of the sealing rings has spiral grooves and a tapered surface to provide the necessary wedge-shaped space at the radially outer regions thereof. The spiral grooves extend from a high pressure fluid side to a low pressure fluid side so as to pump fluid from the high pressure side to the low pressure side. In the normal operation, the fluid film is formed on the sealing surfaces by hydrostatic action and hydrodynamic action, thereby restricting a fluid flow from the high pressure side to the low pressure side. However, in the above end face seal, the spiral grooves extend from the high pressure side to the low pressure side so as to pump fluid in the high pressure side towards the low pressure side. Therefore, under dynamic conditions, the spiral grooves serves to leak fluid from the high pressure side to the low pressure side. That is, the total leakage rate of fluid from the sealing surfaces is equal to the leakage rate caused by pressure difference between high pressure and low pressure plus the leakage rate caused by pumping action of the spiral grooves. Consequently, in the end face seal of this type, it is difficult to reduce leakage of fluid to a certain extent or less as well as the end face seal in Figs. 12 and 13. Further, attention is drawn to EP-A-0 297 381 which relates to a rotary mechanical seal of the gap type. A rotor and a sealing washer having a sealing surface is provided, said sealing surface being adjacent to and confronting a sealing surface on said rotor. The sealing surface is made slightly convex to provide a wedge-shaped space at the radially outer regions of the sealing washer to initiate and maintain the separation of the sealing surfaces under operating conditions. It is therefore an object of the present invention to provide a noncontacting face seal which can reduce leakage of fluid from a high pressure side to a low pressure side. In accordance with the present invention a noncontacting face seal as set forth in claim 1 is provided. Preferred embodiments of the invention are disclosed in the dependent claims. With the structure as defined in claim 1, fluid having a high pressure is introduced into the spaced portion comprising the tapered surface or the recess, the rotating sealing ring is brought out of contact with the stationary sealing ring under hydrostatic force from fluid pressure. Further, when the rotating sealing ring is rotated, under dynamic conditions, the end face seal is exposed to hydrostatic forces from fluid pressure and hydrodynamic forces from the spiral grooves, whereby a fluid film is formed on the sealing surfaces and a gap is formed between the sealing surfaces. The leakage of fluid is restricted by keeping the gap between the sealing surfaces small. That is, the spiral groove pattern pumps fluid (gas) from the low pressure fluid side to the high pressure fluid side to thereby render resistance to fluid flow by pressure difference from the high pressure side to the low pressure side, thus reducing the leakage flow of fluid from the sealing surfaces. The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Fig. 1 is a cross-sectional view showing a noncontacting face seal according to an embodiment of the present invention; Fig. 2 is an end view showing spiral grooves formed on a rotating sealing ring of the noncontacting face seal according to the embodiment of the present invention; Fig. 3 is an enlarged cross-sectional view showing the rotating sealing ring and a stationary sealing ring of the noncontacting face seal according to the embodiment of the present invention; Fig. 4 is a cross-sectional view showing an operation of the noncontacting face seal according to the embodiment of the present invention; Fig. 5 is a graph showing the pressure distribution in a radial direction on the sealing surfaces; Fig. 6 is a cross-sectional view showing a noncontacting face seal according to a second embodiment of the present invention; Fig. 7 is a cross-sectional view showing a noncontacting face seal according to a third embodiment of the present invention; Fig. 8 is a cross-sectional view showing a noncontacting face seal according to a fourth embodiment of the present invention; Fig. 9 is a cross-sectional view showing a noncontacting face seal according to a fifth embodiment of the present invention; Fig. 10 is a cross-sectional view showing a noncontacting face seal according to a sixth embodiment of the present invention; Fig. 11 is a cross-sectional view showing a noncontacting face seal according to a seventh embodiment of the present invention; Fig. 12 is a cross-sectional view showing a conventional end face seal without spiral grooves; and Fig. 13 is an end view showing a sealing surface of the conventional end face seal. DETAILED DESCRIPTION OF THE INVENTION A noncontacting face seal of the present invention will be described below with reference to Figs. 1 through 5. In Fig. 1, a sleeve 2 is fixedly secured to a rotating shaft 1 accommodated in a housing 9. A rotating sealing ring 3 is connected to the sleeve 2 through a pin 20. The rotating sealing ring 3 faces a stationary sealing ring 4 and contacts the stationary sealing ring 4 in a state of surface contact at the sealing surfaces comprising a sealing surface 3S and a sealing surface 4S. Incidentally, the rotating sealing ring 3 is fixedly secured to the sleeve 2 by a sleeve 7 and a retaining nut 8. A stationary sealing ring 4 is pressed against the rotating sealing ring 3 by urging force of coiled springs 10 interposed between a sealing ring retainer 5 and a spring retainer 6. Reference numerals 42, 44, 46, 48, 49 are sealing members such as O ring in Fig. 1. The rotating ring 3 is provided with an outwardly tapered surface 31 which makes the gap between the rotating sealing ring 3 and the stationary sealing ring 4 wider gradually. That is, the tapered surface 31 constitutes a spaced portion and provides the necessary wedge-shaped space between the rotating sealing ring 3 and the stationary sealing ring 4 at the radially outer regions thereof for introducing fluid between two sealing rings 3, 4. The rotating sealing ring 3 is further provided with a flat surface 32 at the central portion of the sealing surface 3S and spiral grooves 33 at the radially inner region of the sealing surface 3S. Fig. 2 shows the sealing surface 3S of the rotating ring 3. In Fig. 2 the tapered surface 31 at the radially outer region (denoted at RO) is located at the high pressure fluid side H, the spiral grooves 33 at the radially inner region (denoted at RI) is located at the low pressure fluid side L. The spiral grooves 33 are open to the low pressure fluid side L and extend from the low pressure fluid side L to the high pressure fluid side H as shown in Fig. 2 so as to pump fluid in the low pressure fluid side L towards the high pressure fluid side H. In Figs. 1 and 3 reference e is the distance between the outer edge of the tapered surface 31 of the rotating sealing ring 3 and the sealing surface 4S of the stationary sealing ring 4 when two sealing rings contact with each other. The dimension e of the tapered surface 31, the inner diameter 2r t of the tapered surface 31, the inside diameter 2r 1 of the sealing surface, the outside diameter 2r 2 of the sealing surface and the balance diameter 2r b are properly arranged so that the gap of the sealing surfaces become small to the utmost extent and the stiffness of fluid film formed on the sealing surfaces enhances. Next, operation of the spiral groove face seal thus constructed will be described below with reference to Fig. 4. When fluid at the high pressure side H enters into the wedge-shaped space between the rotating sealing ring 3 and the stationary sealing ring 4, the sealing surface 3S of the rotating sealing ring 3 is brought out of contact with the sealing surface 4S of the stationary sealing ring 4 by hydrostatic forces from fluid pressure. Relative motion of the rotating sealing ring 3 and the stationary sealing ring 4 is caused by rotating the rotating shaft 1. At this time, the end face seal of the present invention keeps the gap h between two sealing rings 3, 4 small to the utmost extent as shown in Fig. 4 and enables the stiffness of fluid film to enhance. Further, according to the present invention, since the end face seal is provided with the spiral grooves 33 on the sealing surface 3S, the spiral groove pattern pumps fluid (gas) outwardly from the low pressure fluid side L to the high pressure fluid side H. Therefore, fluid flow by pressure difference from the high pressure fluid side H to the low pressure fluid side L meets with resistance by the pumping action of the spiral grooves, thereby reducing the leakage rate of fluid. Fig. 5 shows the pressure distribution in a radial direction on the sealing surfaces. On the graph, the pressure P kgf/cm 2 is plotted on the vertical axis, and the radius r mm on the horizontal axis. In Fig. 5, the noncontacting face seal of the present invention (hereinafter the noncontacting face seal I) is shown using solid line, the conventional noncontacting face seal in Fig. 12 (hereinafter the noncontacting face seal II) using broken line and the noncontacting face seal in U.S. Pat. No. 3,499,653 (hereinafter the noncontacting face seal III) using alternate long and short dash line. In the case of the noncontacting face seal I, the spiral grooves 33 extend to the inner diameter 2r t of the tapered surface 31. The pressure P of the noncontacting face seal I is lower than those of the noncontacting face seals II and III between r 1 and r x in the vicinity of r g (r t ). Therefore, in the noncontacting face seal I, pressure difference between each point and the low pressure side L is small compared with the noncontacting face seals II and III. Thus the leakage rate of the noncontacting face seal I from the high pressure side H to the low pressure side L is smaller than those of the noncontacting face seals II and III. Next, other embodiments of the present invention will be described below with reference to Figs. 6 through 11. Those parts and components in Figs. 6 through 11 which are structurally and functionally identical to those shown in Figs. 1 through 4 are denoted using the same reference numerals. Figs. 6 through 11 show sealing surfaces 3S, 4S of the rotating sealing ring 3 and the stationary sealing ring 4 schematically. Fig. 6 is a cross-sectional view showing a noncontacting face seal according to a second embodiment of the present invention. According to this embodiment, the rotating sealing ring 3 is provided with a recess 38 at the radially outer region thereof in place of the tapered surface 31 of Fig. 3. The recess 38 serves as a spaced portion for introducing fluid between two sealing rings 3, 4. The area where the recess 38 is formed is the same area as the tapered surface 31 of Fig. 3. The second embodiment has the same function and effect as the first embodiment in Figs. 1 through 4. Fig. 7 is a cross-sectional view showing a noncontacting face seal according to a third embodiment of the present invention. According to this embodiment, the rotating sealing ring 3 is provided with a tapered surface 31 in Fig. 7(a), or a recess 38 in Fig. 7(b). The spiral grooves 33 extend beyond the flat surface 32 to the tapered surface 31 (Fig. 7(a)) or the recess 38 (Fig. 7(b)). The pumping action of the spiral grooves 33 of this embodiment is higher than that of the first embodiment in Figs. 1 through 4. Fig. 8 is a cross-sectional view showing a noncontacting face seal according to a fourth embodiment of the present invention. According to this embodiment, the rotating sealing ring 3 is provided with a tapered surface 31 in Fig. 8(a), or a recess 38 in Fig. 8(b). The spiral grooves 33 extend beyond the flat surface 32 to the outer edge of the tapered surface 31 (Fig. 8(a)) or the outer edge of the recess 38 (Fig. 8(b)). The pumping action of the spiral grooves 33 of this embodiment is higher than that of the third embodiment. In a brief summary, the spiral groove area extends to the high pressure fluid side H in the order of Fig. 6, Fig. 7 and Fig. 8, and the pumping action caused by the spiral grooves 33 is higher in the order of Fig. 6, Fig. 7 and Fig. 8. The spiral groove area should be decided in accordance with requirement for thickness of fluid film on the sealing surfaces, the film stiffness and the leakage rate of high pressure fluid. Fig. 9 is a cross-sectional view showing a noncontacting face seal according to a fifth embodiment of the present invention. According to this embodiment, the rotating sealing ring 3 is provided with a tapered surface 31 in Fig. 9(a), or a recess 38 in Fig. 9(b). The spiral grooves 33 extend from inner positions spaced away from the inner circumference of the sealing surface 3S and are located in an area of a flat surface 32 adjacent to the tapered surface 31 (Fig. 9(a)) or the recess 38 (Fig. 9(b)). In this embodiment, a flat surface area A without the spiral grooves 33 is provided on the sealing surface 3S. Therefore, in the case where fluid has low pressure when the machine incorporating the end face seal is stopped, the sealing surfaces do not become noncontact only by hydrostatic force from fluid and thus prevent fluid from leaking out by a contacting portion of the flat surface area A and the sealing surface 4S. Fig. 10 is a cross-sectional view showing a noncontacting face seal according to a sixth embodiment of the present invention. According to this embodiment, the rotating sealing ring 3 is provided with a tapered surface 31 in Fig. 10(a), or a recess 38 in Fig. 10(b). The spiral grooves 33 extend from inner positions spaced away from the inner circumference of the sealing surface 3S. The spiral grooves 33 extend beyond the flat surface 32 to the tapered surface 31 (Fig. 10(a)) or the recess 38 (Fig. 10(b)). In this embodiment, a flat surface area A without the spiral grooves 33 is provided on the sealing surface 3s as well as the fifth embodiment. Therefore, in the case where fluid has low pressure when the machine is stopped, the sealing surfaces do not become noncontact only by hydrostatic force from fluid and thus prevent fluid from leaking out by a contacting portion of the flat surface area A and the sealing surface 4S. Further, the pumping action of the spiral grooves 33 of this embodiment is higher than that of the fifth embodiment. Fig. 11 is a cross-sectional view showing a noncontacting face seal according to a seventh embodiment of the present invention. According to this embodiment, the rotating sealing ring 3 is provided with a tapered surface 31 in Fig. 11(a), or a recess 38 in Fig. 11(b). The spiral grooves 33 extend from inner positions spaced away from the inner circumference of the sealing surface 3S. The spiral grooves 33 extend beyond the flat surface 32 to the outer edge of the tapered surface 31 (Fig. 11(a)) or the outer edge of the recess 38 (Fig. 11(b)). In this embodiment, a flat surface area A without the spiral grooves 33 is provided on the sealing surface 3S as well as the fifth embodiment. Therefore, in the case where fluid has low pressure when the machine is stopped, the sealing surfaces do not become noncontact only by hydrostatic force from fluid and thus prevent fluid from leaking out by a contacting portion of the flat surface area A and the sealing surface 4S. Further, the pumping action of the spiral grooves 33 of this embodiment is higher than that of the sixth embodiment. In the above embodiments, the radially outer region RO of the rotating sealing ring 3 is the high pressure fluid side H, and the radially inner region RI the low pressure fluid side L. However, it should be noted that the radially outer region RO of the rotating sealing ring 3 may be the low pressure fluid side L, and the radially inner region RI the high pressure fluid side H. Further, in the above embodiments, the spiral grooves 33 are provided on the sealing surface 3S of the rotating sealing ring 3, however, the spiral grooves 33 may be provided on the stationary sealing ring 4. As is apparent from the forgoing description, according to the present invention, pumping action is generated by the spiral grooves formed in one of the sealing surfaces so as to render resistance to leakage flow by pressure difference from the high pressure fluid side to the low pressure fluid side, thus reducing leakage rate of fluid from the sealing surfaces. Further, since the spaced portion is provided between two sealing rings by the tapered surface or the recess formed in one of the sealing surfaces, fluid in the high pressure side can enter into the spaced portion to thereby make the sealing surfaces noncontact.

Claims: A noncontacting face seal having a stationary sealing ring (4) and a rotating sealing ring (3) with opposed radially extending sealing surfaces (3S; 4S), said rotating sealing ring (3) being brought out of contact with said stationary sealing ring (4) when hydrostatic force from fluid having high pressure is applied, said seal comprising: spiral grooves (33) formed in one of said sealing surfaces (3S; 4S); and a spaced portion (31; 38) formed in one of said sealing surfaces, said spaced portion extending inwardly from one circumference of said sealing surface at a high pressure fluid side (H) so as to introduce fluid in said high pressure fluid side between said sealing surfaces (3S; 4S), characterized in that said spiral grooves (33) extend from a low pressure fluid side (L) to the high pressure fluid side (H) in a radial direction so as to pump fluid in said low pressure fluid side towards said high pressure fluid side, such that fluid introduced by said spaced portion (31; 38) and flowing from said high pressure fluid side (H) to said low pressure fluid side (L) meets with resistance by the pumping action of said spiral grooves (33). The noncontacting face seal according to claim 1, wherein said spaced portion comprises a tapered surface (31) which is inclined and makes a clearance between said sealing surfaces wider at said high pressure fluid side (H) than at said low pressure fluid side (L). The noncontacting face seal according to claim 1, wherein said spaced portion comprises a recess (38). The noncontacting face seal according to claim 1, wherein said spiral grooves (33) extend from one circumference of said sealing surface and are located in an area of a flat surface (32) adjacent to said spaced portion. The noncontacting face seal according to claim 4, further comprising said spiral grooves extending beyond said flat surface to said spaced portion. The noncontacting face seal according to claim 4, further comprising said spiral grooves (33) extending beyond said flat surface to entire area of said spaced portion. The noncontacting face seal according to claim 1, wherein said spiral grooves extend from inner positions spaced away from one circumference of said sealing surface and are located in an area of a flat surface adjacent to said spaced portion. The noncontacting face seal according to claim 7, further comprising said spiral grooves extending beyond said flat surface to said spaced portion. The noncontacting face seal according to claim 7, further comprising said spiral grooves (33) extending beyond said flat surface to entire area of said spaced portion. The noncontacting face seal according to claim 1, wherein said spiral grooves are formed on said rotating sealing ring (3). The noncontacting face seal according to claim 1, wherein said spiral grooves are formed on said stationary sealing ring (4).

Inventors: KIMURA YOSHIKAZU, TSUBOI HIDEO, KIMURA, YOSHIKAZU, TSUBOI, HIDEO, KIMURA, YOSHIKAZU, C/O EBARA RESEARCH CO., LTD., Tsuboi, Hideo, c/o Ebara Corporation
Applicants: EBARA CORP, EBARA CORPORATION
Application year: 1991
Main classification: F16J15
IPC codes: F16J15