GB2296052A - Mechanical face seals - Google Patents

Abstract

A mechanical face seal has a first seal ring (15) mounted in fixed axial and rotational relationship with respect to a shaft (11) and a second sealing ring (40) mounted in fixed rotational relationship but movable axially of a housing (12). The second sealing ring (40) is mounted with respect to the housing (12) by means of an annular retainer (25). The annular retainer (25) has an inner sleeve formation (32) and a radially separated coaxial outer sleeve formation (35). The second sealing ring (40) is located between the inner and outer sleeve formations (32, 35). The second sealing ring (40) is sealed with respect to the outer sleeve formation (35) by means of first and second sealing rings (50, 51), said first and second sealing means (50, 51) being located at axially separated locations. A radially extending passageway (60) is provided between the internal and external diameters of the second sealing ring (40) the passageway (60) opening to the external diameter of the second sealing ring (40) at a position axially located intermediate of the first and second sealing means (50, 51), sealing means (65) also being provided between the second sealing ring (40) and the inner sleeve formation (32) on the side of the passageway (60) axially remote from the first sealing ring (15). <IMAGE>

Description

MECHANICAL FACE SEALS The present invention relates to mechanical face seals and in particular to mechanical face seals which are subject to internal pressurisation.

Mechanical face seals comprise a pair of sealing rings which are urged axially into sealing engagement, so that one ring can rotate relative to the other while maintaining a fluid-tight seal between the opposed faces.

Conventionally, one or both sealing rings are made of low friction materials such as carbon or graphite or from hardwearing materials such as ceramics. Such materials have low tensile strength which will limit their capacity to withstand internal pressures. As a result, it is normal to design seals so that they are externally pressurised when the materials will be in compression.

For high pressure applications, it is common to use a double seal configuration, where in emergencies, the inboard seal which will normally be externally pressurised, may be subjected to internal pressurisation.

Alternatively, an internally pressurised single seal may be required for external mounting on a pump or agitator.

Hitherto, the problem of low strength when subject to internal pressurisation, has been overcome by shrinking metal rings onto the internal and external diameters of the sealing ring made of low strength material. However, this method of reinforcing the sealing rings makes optimisation of pressure balance and distortion difficult to control with resulting problems in control of the fluid film between the sealing faces.

The present invention provides a mechanical face seal in which sealing rings of homogeneous construction are capable of withstanding significant internal pressurisation.

According to one aspect of the present invention a mechanical face seal comprises a first sealing ring mounted in fixed axial and rotational relationship with respect to one of a pair of relatively rotatable components and a second sealing ring is mounted in fixed rotational relationship but movable axially of the second component and means are provided for urging the second sealing ring axially into sealing engagement with the first sealing ring, the second sealing ring being mounted with respect to said other component by means of an annular retainer, the annular retainer defining an inner sleeve formation and a radially separated coaxial outer sleeve formation, the second sealing ring being located between the inner and outer sleeve formations, first and second sealing means being provided between the second sealing ring and the outer sleeve formation at axially separated locations, a radially extending passageway being provided between the internal and external diameters of the second sealing ring the radially extending passageway opening to the external diameter of the second sealing ring at a position located axially intermediate of the first and second sealing means, sealing means also being provided between the second sealing ring and the inner sleeve formation on the side of the radial passageway axially remote from the first sealing ring.

\ith the seal described above, when the seal is internally pressurised, the pressure fluid will pass through the radial passageway, so that the external diameter of the second sealing ring between the first and second sealing means will be subjected to the same pressure as the internal diameter of the second sealing ring, that portion of the sealing ring being in pressure equilibrium. By suitable positioning and spacing of the first and second sealing means the pressure distortion and stress levels of the second sealing ring may be optimised to control the fluid film between the opposed surfaces of the first and second sealing rings and reduce the likelihood of fracture.

An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings in which: Figure 1 which illustrates in sectional side elevation, a seal in accordance with the present invention; and Figure 2 is a sectional elevation illustrating a modification to the embodiment illustrated in Figure 1.

As illustrated in Figure 1, a seal 10 for providing a fluid-tight seal between a shaft 11 and a housing 12, includes a first sealing ring 1 5 which is mounted on an annular recess 16 in a collar 17 which is secured to the shaft 11 for rotation therewith. The sealing ring 1 5 is sealed to the collar 1 7 by means of elastomeric 0-rings 1 8 and 1 9 and the collar 1 7 is sealed with respect to the shaft 11 by elastomeric 0-ring 20.

A metal retainer 25 includes an inner ring 26 which is a slide fit within a recess 27 in the housing 1 2. The ring 26 is sealed with respect to the housing 1 2 by means of elastomeric 0-ring 28 and is rotationally restrained with respect to the housing 1 2 by means of a plurality of angularly spaced axially extending pins 29 which engage in corresponding bores 30, 31 in the housing 12 and ring 26.

The inner ring 26 defines an inner sleeve formation 32 which extends coaxially of the shaft 11.

A metal outer sleeve member 35 is slidably located coaxially of the ring 26 and inner sleeve formation 32. A cylindrical key 36 is located in a radial bore 37 in the ring 26 and engages in an elongate slot 38 in the outer sleeve member 35, in order to react torque between the outer sleeve member 35 and ring 26. The key 36 is biassed outwardly by spring 39, so that the key 36 may be depressed into the bore 37 to permit the outer sleeve member 35 to be assembled with respect to the ring 26. This design provides a sub-assembly in the form of a cartridge for ease of handling and fitting.

A second sealing ring 40 is located between the inner sleeve formation 32 of ring 26 and the outer sleeve member 35. An internal flange formation 41 on the outer sleeve member 35 abuts the rear end 42 of the second sealing ring 40 and a plurality of angularly spaced spring elements 43 which are located in angularly spaced bores 44 in the ring 26, act against the flange formation 41 to urge the sealing face 45 of sealing ring 40 into sealing engagement with the opposed sealing face 46 of sealing ring 15.

Elastomeric 0-rings 50, 51 located in circumferential grooves 52, 53 in the internal diameter of the outer sleeve member 35 sealingly engage the external diameter of the sealing ring 40. 0-ring 50 is located adjacent to the end of the sealing ring 40 defining the sealing face 45 and 0-ring 51 is located adjacent the rear end 42 of the sealing ring 40. A plurality of angularly spaced radial passageways 60 extend through the sealing ring 40 from the internal to the external diameter thereof. The radial passageways 60 are located axially intermediate of the sealing rings 50 and 51.

The second sealing ring 40 is sealed with respect to the inner sleeve formation 32 by means of an elastomeric 0-ring 65 which is located between a radial face 66 on the sealing ring 40 adjacent the rear end 42 thereof, and an opposed radial face 67 on the inner sleeve formation 32.

The surface 68 of the sleeve formation 32 against which 0-ring 65 seals may be coated with a hard wear resistant material, for example a ceramic or hard metal coating.

Seal 10 described above is intended to form the inboard seal of a double face-to-face seal which under normal operating conditions will be subjected to external pressurisation. Under such conditions, 0-ring 50 will be urged to the lefthand wall of groove 52, 0-ring 51 will be urged to the righthand wall of groove 53 and 0-ring 65 will be urged into engagement with the face 66 of the sealing ring 40, by the external pressure, as illustrated in Figure 1. Under these conditions, when the righthand wall of groove 53 coincides axially with face 66, the rear portion of the seal ring 40 which is disposed to the left of 0-rings 51 and 65, will be in pressure equilibrium and consequently this portion of the sealing ring 40 will not be subject to pressure distortion.

Between the 0-rings 50 and 51 the external diameter of the sealing ring 40 will be subject to the pressure internally of the sealing ring 40 and consequently this portion of the sealing ring 40 will also be in pressure equilibrium. The only pressure differential across the sealing ring 40 will therefore be across the portion from 0-ring 50 to the sealing face 45.

This portion may be dimensioned by suitable positioning of groove 52 to control the length of the portion and appropriate selection of the internal diameter of the sealing ring 40 in that region, in order to achieve the desired rotation of face 45 due to pressure distortion.

The pressure balance of the seal 10 when externally pressurised, that is the degree to which the external pressure will contribute to the axial loading of the sealing face 45 into engagement with sealing face 46, results from the location of the internal and exterenal diameters of end face 45 relative to the diameter of surface 68. The pressure balance may be adjusted as desired by suitable dimensioning of these diameters.

In an emergency, pressurisation of the seal 10 may be reversed, so that high pressure is applied to the internal diameter of the sealing ring 40.

Under these conditions, 0-ring 50 will move to the right of groove 52 and 0-ring 51 will move to the left of groove 53 under the pressure of fluid that is applied to the external diameter of the sealing ring 40 by means of the radial passageways 60. The 0-ring 65 will move against the radial face 67.

Under these conditions, the rear and central portions of the sealing ring 40 will again be in pressure equilibrium and consequently will not be under any tensile load. The only pressure imbalance will again be in the portion of the seal between 0-ring 50 and seal face 45. This portion of the sealing ring may be minimised by locating the groove 52 axially as close as possible to the sealing face 45. The tensile loads on the sealing ring 40 due to the internal pressurisation may consequently be minimised and the weakness of the material will be offset to some extent by the thickness of the sealing ring 40 in this region. Again the position of groove 52 may be selected to provide appropriate rotation of sealing face 45 due to pressure distortion.

Pressure balance when internally pressurised will depend on the location of the internal and external diameters of the end face 45 relative to the diameter of the external circumference of face 66, which again may be adjusted to provide the desired pressure balance.

Pressure distortion of the sealing ring 10 may also be controlled by appropriate adjustment to the relative position of the walls of groove 53 and the faces 66 and 67.

Figure 2 shows a partial view of a modified seal, the view being similar to that shown in Figure 1 but with internal pressurisation. In the modified seal illustrated in Figure 2, the retainer 25 is formed from a single annular component 26' which defines both the inner sleeve formation 32 and an outer sleeve formation 35'. The springs 43 act against a separate thrust member 41' which engages the rear end 42 of the sealing ring 40'.

The sealing ring 40' has an annular formation 70 projecting axially beyond the sealing face 45, the formation 70 extending the outer diameter of the sealing ring 40' so that the right hand wall of groove 52 may be aligned axially with the sealing face 45. In this embodiment, for internal pressurisation the whole of the sealing ring 40' will be in pressure equilibrium. According to a further modification, using a similar configuration to that illustrated in Figure 2, the right hand wall of groove 52 may be disposed to the right of the sealing face 45, so that a portion of the sealing ring 40 will be compressed by the excess pressure acting on its outer diameter, even though the seal is internally pressurised.

While the above embodiments show an outboard seal assembly for a face-to-face double seal arrangement, the invention is equally applicable to either the inboard or outboard seals of double, tandem or dual seal assemblies or to single seals, where equalisation of the pressure across the sealing ring will overcome the tensile loading problems of the materials used and assist control of pressure distortion, when the seal is subjected to internal pressurisation.

Various modifications may be made without departing from the present invention. In the embodiments described above relative rotation between the sealing ring 40 and the outer sleeve member 35 is resisted by the 0rings 50, 51 and 65. Interengaging formations may also be provided on the outer sleeve member 35 or formation 35' and said sealing ring 40 or on the inner sleeve formation 32 and the second sealing ring 40 to provide positive torque reaction therebetween.

It will be appreciated that the material from which the outer sleeve member 35 or formation 35' is formed must be of sufficient strength to withstand the internal pressurisation.

While in the above embodiments the axially movable sealing ring 40 is associated with the housing 12, the sealing ring associated with the shaft 11 may alternatively be axially movable. The elastomeric 0-rings used in the present invention may be replaced by other secondary sealing means, for example spring energised polymer seals.

Claims (11)

1. A mechanical face seal comprising a first sealing ring mounted in fixed axial and rotational relationship with respect to one of a pair of relatively rotatable components and a second sealing ring is mounted in fixed rotational relationship but movable axially of the second component and means are provided for urging the second sealing ring axially into sealing engagement with the first sealing ring, the second sealing ring being mounted with respect to said other component by means of an annular retainer, the annular retainer defining an inner sleeve formation and a radially separated coaxial outer sleeve formation, the second sealing ring being located between the inner and outer sleeve formations, first and second sealing means being provided between the second sealing ring and the outer sleeve formation at axially separated locations, a radially extending passageway being provided between the internal and external diameters of the second sealing ring the radially extending passageway opening to the external diameter of the second sealing ring at a position located axially intermediate of the first and second sealing means, sealing means also being provided between the second sealing ring and the inner sleeve formation on the side of the radial passageway axially remote from the first sealing ring.

2. A mechanical face seal according to Claim 1 in which the retainer is of integral construction.

3. A mechanical face seal according to Claim 1 in which the retainer is formed in two parts, an inner ring defining the inner sleeve formation being fixed axially and rotationally relative to the associated component and an outer sleeve member defining the outer sleeve formation, the outer sleeve member being movable axially of the inner ring and being arranged to move with the second sealing ring as the sealing faces of the first and second sealing rings wear.

4. A mechanical face seal according to Claim 3 in which a flange on the outer sleeve member abuts a rear face of the second sealing ring, biasing means acting between the first ring and the flange to bias the outer sleeve member and second sealing ring axially.

5. A mechanical face seal according to Claim 3 or 4 in which a formation on the inner sealing ring engages a corresponding formation on the outer sleeve member to react to torque therebetween.

6. A mechanical face seal according to Claim 5 in which a pin located in the radial bore in the inner ring engages in an axially elongate aperture in the outer sleeve member.

7. A mechanical face seal according to any one of the preceding claims in which the first and second sealing means comprise elastomeric 0-rings located in grooves in the internal diameter of the outer sleeve formation.

8. A mechanical face seal according to any one of the preceding claims in which the sealing means between the second sealing ring and the inner sleeve formation comprises an elastomeric 0-ring.

9. A mechanical face seal according to Claim 8 in which the elastomeric 0-ring is located between a radial face on the second sealing ring and a radial face on the inner sleeve formation.

1 0. A mechanical face seal according to any one of the preceding claims in which a plurality of angularly spaced radially extending passageways are provided through the second sealing ring.

11. A mechanical face seal substantially as described herein with reference to and as shown in Figures 1 and 2 of the accompanying drawings.