Pressure activated non-contact seals and seal assemblies

Abstract

Pressure activated non-contact seal for a shaft 10 between high-pressure HP region and low-pressure LP region, having carrier 12 radially surrounding shaft 10 supporting seal 22 moveable radially. Bet

Description

Field

[0001] This invention relates to seals and seal assemblies. In particular, the invention relates to pressure activated non-contact seals. The invention also relates to seal assemblies comprising an arrangement of multiple seals. Background

[0002] Seals can be used to provide a pressure barrier around a rotating shaft, such as the shaft of a turbine. In turbines such as gas turbines, it is often necessary to have a shaft that extends through regions of differing fluid pressure, and that seal are provided to maintain the pressure in these regions. One form of seal is a brush seal in which a bunch of filaments extends between the seal and the rotating shaft to maintain a small spacing to ensure a pressure barrier is maintained. As the filaments wear, sealing performance is degraded and eventually the seals must be replaced.

[0003] Wear is a problem for any form of contact seal.

[0004] An object of this invention is to provide a non-contact seal, i.e. one which maintains a small separation between the seal and the shaft that is sufficient to allow rotation while still ensuring an appropriate pressure barrier. It is also desirable that the seal be pressure activated, i.e. that the seal is formed when the pressure across the seal raises to a given level. Summary

[0005] A first aspect of the invention comprises a pressure activated non-contact seal for sealing around the outside of a rotating shaft between a high-pressure region and a low-pressure region, comprising: a seal member carrier spaced radially from the shaft and defining a seal member chamber in fluid communication with the high-pressure region; a seal member supported by the seal member carrier so as to be moveable in a radial direction of the shaft; and a secondary seal mounted between the outer surface of the seal member and an inner surface of the seal member chamber to provide a pressure barrier around the outside of the seal member between the high-pressure region and the low-pressure region; wherein the seal member comprises side walls extending in the radial direction towards the shaft and defining a seal cavity, the radially inner ends of the side walls defining noncontact seal surfaces; and the seal member further comprises a bleed port extending between the seal cavity and the seal member chamber outside the seal member on the high-pressure side of the secondary seal such that in use, high pressure in the seal member chamber urges the seal member towards the shaft until balanced by the pressure in the seal cavity to maintain the non-contact seal surfaces in a non-contact sealing relationship with the shaft.

[0006] In use, a high pressure in the seal member chamber urges the seal member towards the shaft, moving the seal surfaces closer to the shaft. The pressure in the seal cavity also rises due to pressure communication through the bleed port until the pressure in the seal cavity balances the pressure in the seal member chamber to hold the seal surface away from the shaft.

[0007] The seal member side walls can be located at opposite ends of the seal member (i.e. at the high-pressure and low-pressure ends), and one or more intermediate walls can be located between the side walls to define multiple seal cavities. The seal can further comprise a bleed port extending between each seal cavity and the seal member chamber outside the seal member on the high-pressure side of the secondary seal. The sealing behaviour of the seal can be tuned by selecting the size of the seal cavities and bleed port(s).

[0008] The secondary seal can be mounted on the seal member and urged against an inner wall of the seal member chamber (i.e. outwardly sprung). Alternatively, the secondary seal can be mounted on the inner wall of the seal member chamber and urged against an outer surface of the seal member (i.e. inwardly sprung).

[0009] The secondary seal can be located at a position between the high-pressure end and the-low pressure end of the seal member. The exact position will determine how much of the outer surface of the seal member is exposed to high pressure.

[0010] The seal member carrier can comprise an end wall located at the low-pressure end of the seal member carrier and extending towards the shaft such that the low-pressure end of the seal member abuts against the end wall. This can resist axial movement of the seal member due to the pressure drop across the seal.

[0011] The end wall can have a pocket formed facing the low-pressure end of the seal member carrier, wherein the pocket is in pressure communication with the seal member chamber outside the seal member on the high-pressure side of the secondary seal. A pressure port can extend between the pocket and the seal member chamber outside the seal member on the high-pressure side of the secondary seal, or between the pocket and a seal cavity having a bleed port extending to the seal member chamber outside the seal member on the high-pressure side of the secondary seal.

[0012] Alternatively, the seal member carrier can comprise an end wall located at the high-pressure end of the seal member carrier and extending towards the shaft, and a leaf spring extends between the end wall and the high-pressure end of the seal member. The leaf spring can resist the axial load due to pressure drop across the seal and can guide the movement of the seal member.

[0013] The leaf spring can comprise a pair of leaf springs spaced apart in a radial direction.

[0014] A second aspect of the invention comprises a seal assembly comprising multiple seals arranged circumferentially around the shaft.

[0015] The seal assembly can further comprise a seal carrier, and each seal can comprise a formation that engages with a corresponding formation on the seal carrier to resist rotational movement of the seal. This can assist in preventing the seals rotating with the shaft.

[0016] The seal assembly can further comprise springs, such as coil springs or leaf springs between adjacent seals arranged to urge the adjacent seals apart. This will cause the seals to be pushed away form the shaft when not activated by high pressure.

[0017] The edges of adjacent seals can be stepped and the stepped edges interengaged to prevent a direct path extending between adjacent seals. The steps can be in the radial and / or axial directions.

[0018] Further aspects of the invention are described below in relation to the drawings. Description of the Drawings

[0019] Figures 1 and 2 show a first embodiment of a seal in an inactivated state and an activated state.

[0020] Figures 3 and 4 show alternative forms of a sealing member for the embodiment of Figures 1 and 2.

[0021] Figures 5 and 6 show further alternative forms of a sealing member for the embodiment of Figures 1 and 2.

[0022] Figures 7and 8 show still further alternative forms of a sealing member for the embodiment of Figures 1 and 2.

[0023] Figure 9 shows an end view of sealing members as shown in Figure 7 or 8.

[0024] Figure 10 shows a partial view of a seal assembly according to the invention.

[0025] Figures 11 and 12 show alternative embodiments of the seal assembly of Figure 10.

[0026] Figures 13 and 14 show axial and radial partial views of adjacent seals in an assembly.

[0027] Figures 15 and 16 show a second embodiment of a seal in an inactivated state and an activated state.

[0028] Figures 17 and 18 show an alternative form of the embodiment of Figures 15 and 16.

[0029] Figure 19 shows details of the embodiment of Figures 15 to 18. Detailed Description

[0030] The seal shown in Figures 1 and 2 is a cross-section through a seal for use with a rotating shaft 10 such as a shaft extending through a gas turbine between a high-pressure region HP and a low-pressure region LP that rotates about an axis X-X. The seal comprises a seal member carrier 12 spaced from the shaft 10. The inner part of the seal member carrier 12 defines a seal member chamber 14. The low-pressure end of the seal member carrier 12 has an end wall 16 extending towards the shaft 12. A locating grove 18 is provided in the inner wall of the seal member chamber 14 and an inwardly sprung secondary sealing ring 20 is mounted in the groove 18. Figure 2 shows an embodiment in which the seal member carrier 12 is made in two parts for ease of assembly. In this case, the groove 18 can be formed at the interface between the two parts.

[0031] A seal member 22 is located in the seal member chamber 14 so as to be moveable in the radial direction r-r. The secondary sealing ring 20 is urged into contact with the outer surface 24 of the seal member 22 to form a pressure barrier part way along the seal member chamber 14. The seal member carrier is open to the high-pressure fluid at one end 26, and to low-pressure fluid at the other end 28. Consequently, the seal member chamber 14 has a high-pressure zone on the high-pressure side of the secondary seal 20 and a low-pressure zone on the low-pressure side of the secondary seal 20.

[0032] The seal member 22 has end walls 30, 32 that extend towards the shaft 10. Intermediate walls 34, 36 are located between the end walls 30, 32. The intermediate walls are substantially parallel to the end walls 30, 32. The ends 38, 40, 42, 44 of the end walls 30, 32 and intermediate walls 34, 36 are level with each other and define non-contact seal surfaces. The end walls 30, 32 and intermediate walls 34, 36 define seal cavities 46, 48, 50.

[0033] Each cavity 46, 48, 50 communicates with the high-pressure zone of the seal member chamber 14 via a respective bleed port 52, 54, 56.

[0034] In use, the seal is in the configuration shown in Figure 1 due to the effect of springs in the mounting (described below). The pressure at the high-pressure end HP builds. While the spaces between the ends 38, 40, 42, 44 and the bleed ports 52, 54, 56 allow fluid to pass across the seal, the spaces and port sizes are sufficiently small that there is resistance to fluid flow and a pressure drop is created. The effect of this pressure drop is that the higher pressure acting on the outer surface of the seal member 22 urges it towards the shaft 10, closing the space between the ends 38, 40, 42, 44 and the outer surface of the shaft 10. The fluid continues to enter the cavities 46, 48, 50 through the bleed ports 52, 54, 56 but pressure rises due to the reduced spacing of the ends 38, 40, 42, 44 from the shaft 10 until the pressure in the cavities 46, 48, 50 balances the pressure in the high-pressure zone acting on the outer surface of the seal member 22. At this point (Figure 2), the ends 38, 40, 42, 44 are separated from the shaft 10 by a very small distance so there is no contact but still sufficient resistance to fluid flow to maintain the pressure difference across the seal. The seal is self-adjusting; if the space between the ends 38, 40, 42, 44 becomes too small, the pressure in the cavities 46, 48, 50 builds, lifting the seal member 22 away from the shaft until the pressure drops due to the wider spacing.

[0035] The seal member carrier end wall 16 prevents axial movement of the seal member 22 due to the pressure drop across the seal by abutting engagement with the low-pressure end wall 32 of the seal member 22.

[0036] In the embodiment of Figures 1 and 2, there are three approximately equal cavities. In other embodiments the number and relative sizes of the cavities can be varied. Figure 3 shows an embodiment with a seal member 22a having one intermediate wall 58 and two cavities 60, 62. In this case, the intermediate wall 58 is spaced towards the low-pressure end of the seal member 22a so that the cavities are of dissimilar sizes. In addition, instead of the groove 18 in the seal member carrier 12 with an inward sprung seal 20, the seal member 22a has a groove 64 in its outer surface with an outward sprung sealing ring 66 which engages the inner wall of the seal member carrier chamber 14.

[0037] Figure 4 shows an alternative sealing member 22b for use in the embodiment of Figure 3. In this case there are no intermediate walls and only a single cavity 68.

[0038] It is not necessary that a bleed port is provided for each cavity. Also, the dimension of the bleed ports need not be identical. The number and relative sizes of the cavities and bleed ports can be adjusted according to requirements.

[0039] The position of the secondary seal between the ends of the seal member carrier chamber defines the size of the high-pressure zone and hence the force that can be applied to the seal member 22.

[0040] Figure 5 shows another embodiment similar to that of Figure 2. As before, the seal member carrier end wall 16 prevents axial movement of the seal member 22 due to the pressure drop across the seal by abutting engagement with the low-pressure end wall 32 of the seal member 22. In use, friction between the end walls 16, 32 might inhibit free movement of the sela member 22. In the embodiment of Figure 5, the seal member end wall 32 has a pressure balance pocket 70 that faces the seal member carrier end wall 16. The pressure balance pocket 70 is connected to the high-pressure zone of the carrier chamber 14 by means of a pressure balance feed port 72. This reduces the friction between the contact surfaces when pressure is applied across the seal.

[0041] An alternative form of seal member 22 is shown in Figure 6 in which the pressure balance feed port 72 is replaced by an end wall port 74 which connects the pressure balance pocket 70 to the adjacent cavity 50 which in turn is connected to the high-pressure zone of the carrier chamber 14 by means of the bleed feed port 56.

[0042] Figures 7 and 8 show further variants of the seal member 22 shown in Figures 5 and 6. In each case the seal member end wall 32 is replaced by an enlarged end wall 76. This in turn allows for an enlarged pressure balance pocket 78 which has approximately the same area as that of the upstream end wall 30 of the seal member 22. The enlarged pressure balance pocket 78 is connected to the high-pressure zone of the carrier chamber 14 by means of a pressure balance feed port 72 or by an end wall port 74 which connects the pressure balance pocket 70 to the adjacent cavity 50 which in turn is connected to the high-pressure zone of the carrier chamber 14 by means of the bleed feed port 56.

[0043] While Figures 5 to 8 only show one pressure balance feed port 72 of end wall port 74, more than one can be provided. Figure 9 shows an end view of the seal member 22 having two pressure balance fed ports 72 opening into enlarged pressure balance pocket 78.

[0044] The invention also provides a seal assembly as shown in part in Figure 10. The seals described above are intended to fit around a rotating shaft. This is achieved by using a plurality of arcuate seal segments 100, 102, 104, each of which comprises a seal such one of those described above and that is held in a circumferential arrangement around the shaft by a seal carrier 106. Each seal has a lug 108 that engages in a slot 110 in the seal carrier 106. The inter-engagement of these formations prevents rotation of the seals with the shaft.

[0045] In order to maintain the seals paced away from the shaft at start up, springs are provided between adjacent seals 100, 102, 104 to urge each other apart. These can be coil springs 112 (Figure 11) or wishbone / leaf springs 114 (Figure 12).

[0046] In order to prevent leakage in the gaps between adjacent seals 100, 102, 104, the edges of the seals can be provided with inter-engaging stepped formations. The steps can be in the radial direction 116 (Figure 13) and / or in the axial direction 118 (Figure 14).

[0047] Figures 15 and 16 show a second embodiment of a seal according to the invention. In this embodiment, the seal member 170 has generally the same configuration as that of Figure 1. In this embodiment, the seal member carrier 172 has a different configuration. The low-pressure end 174 of the seal member carrier 172 has a groove 176 mounting the inwardly sprung secondary sealing ring 178. The high-pressure end 180 of the seal member carrier 172 is spaced from the high-pressure end 182 of the seal member 170. A pair of leaf springs 184, 186 extends through the seal member carrier chamber 188 between the high-pressure end 180 of the seal member carrier 172 and the high-pressure end 182 of the seal member 170. The leaf springs 184, 186 are spaced in the radial direction.

[0048] The leaf springs 184, 186 resist axial load on the seal member 170 and allow controlled radial movement of the seal member 170 when active by high-pressure so that is remains parallel to the shaft surface (Figure 16).

[0049] Figures 17 and 18 show an alternative embodiment to that shown in Figures 15 and 16. In this embodiment, the groove 176 in the carrier 172 and inwardly sprung secondary sealing ring 178 are replaced by a groove 190 in the outer surface of the seal member 170a mounting an outwardly sprung secondary sealing rung 192 which acts on the inner surface of the carrier 172 at the low-pressure end.

[0050] As is described in more detail below, the seal member 170 has an arcuate form. Figure 19 shows the mounting of the leaf springs 184, 186 on the seal member 170. The leaf springs 184, 186 are planar and act in one plane only.

[0051] Further changes can be made within the scope of the invention.

Claims

19 02 251. A pressure activated non-contact seal for sealing around the outside of a rotating shaft between a high-pressure region and a low-pressure region, comprising:a seal member carrier spaced radially from the shaft and defining a seal member chamber in fluid communication with the high-pressure region;a seal member supported by the seal member carrier so as to be moveable in a radial direction of the shaft; anda secondary seal mounted between the outer surface of the seal member and an inner surface of the seal member chamber to provide a pressure barrier around the outside of the seal member between the high-pressure region and the low-pressure region;whereinthe seal member comprises side walls extending in the radial direction towards the shaft and defining a seal cavity, the radially inner ends of the side walls defining non-contact seal surfaces; andthe seal member further comprises a bleed port extending between the seal cavity and the seal member chamber outside the seal member on the high-pressure side of the secondary seal such that in use, high pressure in the seal member chamber urges the seal member towards the shaft until balanced by the pressure in the seal cavity to maintain the non-contact seal surfaces in a non-contact sealing relationship with the shaft.

2. A seal as claimed in claim 1, wherein the seal member side walls are located at opposite ends of the seal member, and one or more intermediate walls are located between the side walls to define multiple seal cavities.19 02 253. A seal as claimed in claim 2, further comprising a bleed port extending between each seal cavity and the seal member chamber outside the seal member on the high-pressure side of the secondary seal.

4. A seal as claimed in claim 1,2, or 3, wherein the secondary seal is mounted on the seal member and is urged against an inner wall of the seal member chamber.

5. A seal as claimed in claim 1,2, or 3, wherein the secondary seal is mounted on the inner wall of the seal member chamber and is urged against an outer surface of the seal member.

6. A seal as claimed in any preceding claim, wherein the secondary seal is located at a position between the high-pressure end and the-low pressure end of the seal member.

7. A seal as claimed in any preceding claim, wherein the seal member carrier comprises an end wall located at the low-pressure end of the seal member carrier and extending towards the shaft such that the low-pressure end of the seal member abuts against the end wall.

8. A seal as claimed in claim 7, wherein the end wall has a pocket formed facing the low pressure end of the seal member carrier, wherein the pocket is in pressure communication with the seal member chamber outside the seal member on the high-pressure side of the secondary seal.

9. A seal as claimed in claim 8, wherein there is a pressure port extending between the pocket and the seal member chamber outside the seal member on the high-pressure side of the secondary seal, or between the pocket and a seal cavity having a bleed port extending to the seal member chamber outside the seal member on the high-pressure side of the secondary seal.

10. A seal as claimed in any of claims 1 to 6, wherein the seal member carrier comprises an end wall located at the high-pressure end of the seal member carrier and extending towards the shaft, and a leaf spring extends between the end wall and the high-pressure end of the seal member.19 02 2511. A seal as claimed in claim 10 wherein the leaf spring comprises a pair of leaf springs spaced apart in a radial direction.

12. A seal assembly comprising multiple seals as claimed in any preceding claim arranged circumferentially around the shaft.

13. A seal assembly as claimed in claim 12, further comprising a seal carrier, wherein each seal comprises a formation that engages with a corresponding formation on the seal carrier to resist rotational movement of the seal.

14. A seal assembly as claimed in claim 12 or 13, further comprising springs between adjacent seals arranged to urge the adjacent seals apart.

15. A seal assembly as claimed in claim 12, 13, or 14, wherein the edges of adjacent seals are stepped and the stepped edges are inter-engaged to prevent a direct path extending between adjacent seals.

16. A seal assembly as claimed in claim 15, wherein the steps are in the radial and / or axial directions.

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