GB2037380A - Seals - Google Patents

Abstract

A seal 16 between axially aligned casings 13, 14 of a jet engine compressor remains effective when axial and/or radial relative movements occur due to differential thermal comparison of the casings. The seal comprises a support member 17 having an integral sealing element 19 urged by a spring 28 into engagement with a radial face 23 of one casing 13, the member 17 having riveted thereto a sealing element 18 which, under its own resilience, bears on the periphery of the other casing 14. External gas loads which are greater than internal gas loads enhance the sealing pressures. <IMAGE>

Description

SPECIFICATION Sealing Means This invention relates to sealing means and in particular to sealing means suitable for effecting a seal between two duct members.

When two duct members adapted to contain a fluid flow are joined so that they share a common fluid flow, it is difficult to effect a seal between them which allows for a limited amount of relative movement between the members. For example an axial flow compressor for a gas turbine often comprises a number of separate casings which contain the various stages of aerofoil blades necessary to achieve air compression. It is important that no leakage should occur between the casings otherwise the efficiency of the compressor would be impaired. However, it is equally important that some limited degree of relative movement between the casings should be permitted in order to allow for the different rates of thermal expansion encountered during engine operation cycles.Thus both relative axial and radial movement between adjacent casings may be observed as an engine runs up to its normal operating temperature.

It is an object of the present invention to provide sealing means adapted to maintain a seal between two duct members which seal permits a limited degree of relative movement between the duct members without the seal being broken.

According to the present invention, sealing means suitable for effecting a seal between adjacent first and second duct members comprises a support member carrying primary and secondary sealing elements, said primary sealing element being adapted to surround and be resiliently urged into sealing engagement with the first of said duct members, said secondary sealing element being adapted to be resiliently urged into sealing engagement with the second of said duct members in a direction generally normal to that in which said primary sealing element is urged.

Said primary sealing element is preferably of substantially U-shaped cross-section and formed from a resilient material.

Said secondary sealing element preferably comprises a rib located on said support member, resilient means being provided to urge said support member in such a direction that said rib is urged in turn into sealing engagement with said second duct member.

Said second duct member preferably has a mouth provided with a generally channel-shaped lip having opposed faces substantially normal to the axis of said second duct, said support member being situated within said lip at least partially between said opposed faces so that said rib is resiliently biassed into sealing engagement with one of said opposed faces by the action of said resilient means betweenthe other of said opposed faces of said support member.

Said support member is preferably provided with a member adapted to locate across the open end of said U-shaped cross-section primary sealing element so as to define an enclosed chamber therewith, said so-defined chamber being supplied in operation with pressurised fluid whereby the chamber distorts in such a manner that sealing engagement between said primary sealing element and said first duct member is enhanced.

Said U-shaped cross-section primary sealing element is preferably attached to said support member in such a manner that when said primary sealing element is pressurised and thus distorted, it additionally exerts a force upon said support member which enhances the force exerted by said resilient means upon said support member in urging said rib into sealing engagement with said second duct member.

Said generally channel-shaped lip on the mouth of said second duct member may be detachable therefrom.

The invention will now be described by way of example with reference to the accompanying drawing which is a partially sectioned side view of part of the compressor of an axial flow gas turbine.

With reference to the drawing, the compressor 10 of an axial flow gas turbine engine comprises alternate stages of rotary and stationary aerofoil blades 11 and 12 contained within casings 13, 14 and 1 5. Under engine operating conditions some degree of relative movement, both in axial and radial directions, occurs between the casings 13 and 14. This is the inevitable result of temperature changes which occur during typical engine operating cycles. In order to ensure that the leakage of air into the compressor 10 is prevented, a seal 1 6 in accordance with the present invention is provided between the casings 13 and 14.

The seal 1 6 comprises an annular support member 1 7 which carries primary and secondary sealing elements 1 8 and 1 9 respectively. The primary sealing element 18 is an annular substantially U-shaped cross-section member having an extended flange-like portion 20 by means of which it is attached to one face of the support member 17 by rivets. An annular piece 21 also riveted to the same face of the support member 1 7 extends across the open end of the primary sealing element 1 8 so as to define an annular chamber 22 therewith. The primary sealing element 18 is formed from a resilient material so that it is urged by its inherent resilience into sealing engagement with the radially outer surface of the casing 14.

The secondary sealing element 19 is constituted by a rib provided on the opposite face of the support member 1 7 to that which the primary sealing element 18 and annular piece 21 are attached.

The seal 1 6 is positioned partially between the opposed faces 23 and 24 of a generally channelshaped lip 25 provided on the mouth 26 of the casing 13. The opposed faces 23 and 24 are normal to the axis of the casing 13. In this particular case, the lip 25 is attached to the mouth 24 by a series of boits 27 one of which can be seen in the drawing. It will be appreciated however that the lip 25 could in certain circumstances be at least partially formed from the mouth 24 so as to be partially integral therewith. For the purposes of the present invention the lip 25 is to be considered as a portion of the duct 1 3 whether it is at least partially integral therewith or is a separate member fixedly attached thereto.

An annular ripple spring 28 is provided within the lip 25 adjacent face 24. The ripple spring 28 is positioned so as to resiliently urge the annular support member 17 towards the opposite lip face 23 so that the secondary sealing element 1 9 is in turn resiliently biassed into sealing engagement with the lip face 23. The direction in which the secondary sealing element 1 9 is urged into sealing engagement is consequentiy generally normal to the direction in which the primary sealing element 1 8 is urged. This arrangement permits limited relative movement, both axial and radial (with respect to the axes of the casings 13 and 14) between the casings 1 3 and 14 without the seal 16 being broken.Thus whichever form of limited relative movement occurs between the casings 13 and 14 each of the seals provided by the sealing elements 1 8 and 19 will remain intact.

The clearances between the support member 20 and the lip 25 are arranged so as to allow limited relative movement without fouling.

The annular piece 21 is provided with a number of apertures 29 which permit the entry of pressurised air present in the area 30 outside the compressor 10 into the annular chamber 22.

Now the air pressure in the area 30 is, during engine operation, higher than the air pressure at 31 on the side of the primary sealing element 1 8 which is exposed to the air stream passing between the casings 13 and 14. Consequently the higher air pressure within the annular chamber 22 results in the primary sealing element 1 9 distorting. This in turn results in the pressure exerted by the primary sealing element 1 8 on the radially outer surface of the casing 14 due to its resilience being enhanced. Moreover this distortion of the primary sealing element 1 8 also results in a force being exerted by the sealing element 18 upon the annular support member 1 7 in a generally axial direction.This tends to enhance the force already exerted by the ripple spring 28 so that sealing between the secondary sealing element 19 and the lip face 23 is in turn enhanced. The force exerted by the ripple spring 28 is still further enhanced by the air pressure difference between the areas 30 and 31. Thus air pressure acting upon the assembly comprising the annular support member 1 7, the primary sealing element 18 and the annular piece 21 will result in an increase in the force with which the secondary sealing element 1 9 is urged into engagement with the face 23.

It will be seen therefore that the seal 1 6 provides a seal between the casings 1 3 and 14 at all times from engine starting up to engine cruise conditions despite limited relative movement between the casings as their temperatures alter.

In order to prevent excessive wear occurring, a suitable antifriction coating is provided on those portions of the casing 14 and lip face 23 which are abutted by the sealing elements 18 and 1 9.

Claims (8)

Claims

1. Sealing means suitable for effecting a seal between adjacent first and second duct members comprising a support member carrying primary and secondary sealing elements, said primary sealing element being adapted to surround and be resiliently urged into sealing engagement with the first of said duct members, said secondary sealing element being adapted to be resiliently urged into sealing engagement with the second of said duct members in a direction generally normal to that in which said primary sealing element is urged.

2. Sealing means as claimed in claim 1 wherein said primary sealing element is of substantially U-shaped cross-section and formed from a resilient material.

3. Sealing means as claimed in claim 1 or claim 2 wherein said secondary sealing element comprises a rib located on said support member, resilient means being provided to urge said support member in such a direction that said rib is urged in turn into sealing engagement with said second duct member.

4. Sealing means as claimed in any one of claims 1 to 3 wherein said second duct member has a mouth provided with a generally channelshaped lip having opposed faces substantially normal to the axis of said second duct, said support member being situated within said lip at least partially between said opposed faces so that said rib is resiliently biassed into sealing engagement with some of said opposed faces by the action of said resilient means between the other of said opposed faces and said support member.

5. Sealing means as claimed in any one of claims 2 to 4 wherein said support member is provided with a member adapted to locate across the open end of said U-shaped cross-section primary sealing element so as to define an enclosed chamber therewith, said so defined chamber being supplied in operation with pressurised fluid whereby the chamber distorts in such a manner that sealing engagement between said primary sealing element and said first duct member is enhanced.

6. Sealing means as claimed in claim 5 wherein said U-shaped cross-section primary sealing element is attached to said support member in such a manner that when said primary sealing element is pressurised and thus distorted, it additionally exerts a force upon said support member which enhances the force exerted by said resilient means upon said support member in urging said rib into sealing engagement with said second duct member.

7. Sealing means as claimed in any one of claims 4 to 6 wherein said generally channel shaped lip on the mouth of said second duct member may be detachable therefrom.

8. Sealing means substantially as hereinbefore described with reference to and as shown in the accompanying drawings.