GB2293215A

GB2293215A - Shaft seal

Info

Publication number: GB2293215A
Application number: GB9416842A
Authority: GB
Inventors: Norman Kenneth Bowers
Original assignee: James Walker and Co Ltd
Current assignee: James Walker and Co Ltd
Priority date: 1994-08-19
Filing date: 1994-08-19
Publication date: 1996-03-20
Also published as: GB9416842D0

Abstract

Sealing apparatus for a rotating shaft, comprising a housing 12, and one or more main sealing rings 14 mounted in the housing, in which the or each main sealing ring is mounted in an annular cage 22 positioned within an annular recess in the housing and able to move radially relative to the recess, a first face of the cage on the low-pressure side sliding against a first face of the recess, and a second face of the cage on the high-pressure side sliding against a second face of the recess, and in which there is provided a first annular seal 50 between the first face of the cage and the first face of the recess, a second annular seal 54 between the second face of the cage and the second face of the recess, a third annular seal 58, of larger diameter than the second seal, between the second face of the cage and the second face of the recess, first passage means to allow the fluid to be sealed to enter the space between the cage and the recess in the housing, in the region radially outwards of the first and third seals, so that the pressure of the fluid to be sealed is applied to the cage in that region, and second passage means connecting the space between the second and third seals to the low-pressure side of the housing, the area of the second face of the cage between the second 54 and third seals 58, being substantially equal to the area of the first face of the cage radially inwards of the first seal 50, so that the pressure of the fluid to be sealed produces a net axial force on the cage which is zero or very low. <IMAGE>

Description

Shaft seal This invention relates to sealing apparatus for rotating shafts.

The invention relates more particularly to sealing apparatus for use with rotating shafts are subject to high working pressure.

It is an object of this invention to provide an improved sealing apparatus.

This invention consists in sealing apparatus for a rotating shaft, comprising a housing, and one or more main sealing rings mounted in the housing, in which the or each main sealing ring is mounted in an annular cage positioned within an annular recess in the housing and able to move radially relative to the recess, a first face of the cage on the low-pressure side sliding against a first face of the recess, and a second face of the cage on the high-pressure side sliding against a second face of the recess, and in which there is provided a first annular seal between the first face of the cage and the first face of the recess, a second annular seal between the second face of the cage and the second face of the recess, a third annular seal, of larger diameter than the second seal, between the second face of the cage and the second face of the recess, first passage means to allow the fluid to be sealed to enter the space between the cage and the recess in the housing, in the region radially outwards of the first and third seals, so that the pressure of the fluid to be sealed is applied to the cage in that region, and second passage means connecting the space between the second and third seals to the low-pressure side of the housing, the area of the second face of the cage between the second and third seals being substantially equal to the area of the first face of the cage radially inwards of the first seal, so that the pressure of the fluid to be sealed produces a net axial force on the cage which is zero or very low.

Preferably, each of the first, second and third seals is a sealing ring, such as an O-ring or D-ring mounted in a recess in the associated face of the cage, and the second passage means1 comprises one or more passages extending through the body of the cage from the region of the second face of the cage between the recesses for the second and third seals to a face of the cage in the region between the first seal and the main sealing ring.

Suitably, the main sealing ring is of the kind energised by the pressure of the fluid to be sealed, the fluid entering a space between the radially outer face of the sealing ring and the cage, and the first passage means comprises one or more passages in the cage connecting the said space to the space between the radially outer face of the cage and recess in which the cage moves.

The main sealing ring may, for example, be of the type described in European patent EP-O 125 896.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-section through a sealing apparatus in accordance with the invention, and Figure 2 shows an embodiment similar to that of Figure 1, but employing multiple sealing rings.

Referring to the drawings, a sealing apparatus is provided for sealing the space between a shaft 10 and metalwork surrounding the shaft. The apparatus consists of a housing 12 containing a main sealing ring 14. A metal shaft sleeve 16 fixed to the shaft 10 provides a wear-resistant cylindrical surface 18 against which the sealing ring 14 acts. It will be appreciated that in some applications the sealing ring could act directly against the shaft.

The main sealing ring 14 is contained in a recess 20 in a cage 22 in the housing 12. The main sealing ring 14 consists of a sleeve 24 of plastics, such as the bonded rubber composite sold under the name Texilon (registered trade mark), surrounded by an elastomeric energising ring 26. The elastomeric ring has lips engaging the axial end face 28 of the recess 20 in which it is contained. Ports 28 in the elastomeric ring 26 on the high pressure side allow the working fluid to flow into the space 30 between the sealing ring 14 and the radially outer face of the recess 20, so that a radially inward pressure is exerted on the sealing ring. Each sealing ring 14 may be of the same type as that described in the above-mentioned European patent EP-0125896.

The cage 22 consists of an annular body which fits into a recess 32 in the housing 12. The radially outer face 34 of the cage 22 has a diameter less than the diameter of the cylindrical face 36 of the recess 32, so that the cage can move radially relative to the housing 12. The radially inner face 38 of the cage 22 is lined, on the high pressure side of the recess 20, with a bearing 40, having a diameter slightly greater than the outside diameter of the shaft sleeve 16. The axial end face 42 of the cage 22, on the low pressure side, slides against face 44 of the recess 32 in the housing 12. The opposite axial end face 46 of the cage, on the high pressure side, slides against face 48 of the recess 32. A seal, such as an O-ring or D-ring 50, is mounted in a groove 52 formed in the axial end face 42 on the low pressure side of cage 22.A second seal 54 is mounted within a groove 56 in the axial end face 48 on the high pressure side of cage 22. A third seal 58, of diameter greater than that of seal 54, is mounted in a groove 60 in the end face 48 on the high pressure side of the cage 22. For a reason explained below, the area "B" of face 46 between the recesses 56 and 60 is substantially equal to the area "A" of face 44 between the recess 52 and the inner face 38 of the cage 22.

Ports 62 in the cage 22 connect the space 30 in the recess 20 radially outwards of the main sealing ring 14 with the space 64 between the radially outer face 34 of the cage 22 and the face 36 of the recess 32. A drain passage 66 in the cage 22 opens at one end into the face 46, in the region between the recesses 56 and 60 and opens at its other end into the inner face 38 of the cage 22, on the low pressure side of the main sealing ring 14.

In use, the pressure of the fluid to be sealed is communicated to space 30 through ports 28 in the main sealing ring 14, and through ports 62 to the space 64 in the recess 32 in housing 12. Leakage of the fluid from space 64 to the low pressure side of the recess 32 is prevented by the seal 50. The seals 54 and 58 on the high pressure side of the cage 22 prevent the pressure of the fluid being applied to the area of face 46 between the recesses 56 and 60, which is connected to the low pressure side of the main sealing ring 14 through passage 66. The pressure of the fluid is therefore applied to both axial end faces of the cage 22 except for the area "A" on the low pressure side and the area "B" on the high pressure side, which are subject to the pressure on the low pressure side of the main sealing ring 14.Since the areas "A" and "B" are substantially equal, so that the areas of the two axial end faces of the cage 22 to which the pressure of the fluid is applied are also substantially equal, the net axial force exerted on the cage 22 by the pressure of the fluid is substantially zero. This balancing of the pressure exerted on the cage 22 enables the sealing apparatus to withstand very high peak pressures.

Since the cage 22 can float radially relative to the housing 12, on the fluid lubricated bearing 40, the sealing apparatus can accommodate radial movements of the shaft. Rubber springs (not shown) may be provided between the cage 22 and the housing 12. In particular, rubber springs (not shown) may be provided at the bottom of the housing, to support the weight of the cage 22.

Since the housing 12 does not need to float radially, it can be connected rigidly to the surrounding metal-work by any suitable means. The housing can be made as massive as required to cope with any anticipated high transient pressure.

Figure 2 shows an embodiment similar to that of Figure 1, but having a series of main sealing rings 70, 72 and 74, each mounted in a separate cage 76, 78 and 80. Each cage fits into a corresponding recess 82, 84 and 86 in the housing 12, and is constructed to provide a pressure balance as in the embodiment of Figure 1. The housing 12 consists of separate components 88, 90 and 92 connected together and to the surrounding metal-work by a stud 94.

The radially inner face of cage 76 is lined with a bearing 77, on each side of the recess containing the sealing ring 70. The cages 78 and 80 are similarly lined with bearings 79 and 81. This has the advantage that the bearings act independently of one another, so that if the bearing on one of the cages fails, the bearings on the other two continue to function, enabling the housing 12 to move radially to accommodate radial movements of the shaft 10.

It will be appreciated that the invention could be applied to apparatus employing main sealing rings of types other than that of the described embodiments.

Claims

Claims:

1. Sealing apparatus for a rotating shaft, comprising a housing, and one or more main sealing rings mounted in the housing1 in which the or each main sealing ring is mounted in an annular cage positioned within an annular recess in the housing and able to move radially relative to the recess, a first face of the cage on the low-pressure side sliding against a first face of the recess, and a second face of the cage on the high-pressure side sliding against a second face of the recess, and in which there is provided a first annular seal between the first face of the cage and the first face of the recess, a second annular seal between the second face of the cage and the second face of the recess, a third annular seal, of larger diameter than the second seal, between the second face of the cage and the second face of the recess, first passage means to allow the fluid to be sealed to enter the space between the cage and the recess in the housing, in the region radially outwards of the first and third seals, so that the pressure of the fluid to be sealed is applied to the cage in that region, and second passage means connecting the space between the second and third seals to the low-pressure side of the housing, the area of the second face of the cage between the second and third seals being substantially equal to the area of the first face of the cage radially inwards of the first seal, so that the pressure of the fluid to be sealed produces a net axial force on the cage which is zero or very low.

2. Apparatus as claimed in claim 1, in which each of the first, second and third seals is a sealing ring, such as an O-ring or D-ring mounted in a recess in the associated face of the cage, and the second passage means, comprises one or more passages extending through the body of the cage from the region of the second face of the cage between the recesses for the second and third seals to a face of the cage in the region between the first seal and the main sealing ring.

3. Apparatus as claimed in claim 1 or claim 2 in which the main sealing ring is of the kind energised by the pressure of the fluid to be sealed, the fluid entering a space between the radially outer face of the sealing ring and the cage, and the first passage means comprises one or more passages in the cage connecting the said space to the space between the radially outer face of the cage and recess in which the cage moves.