MECHANICAL FACE SEALS

Abstract: A mechanical face seal comprises a first seal face member l2 associated in fixed relationship and sealed with respect to one component l0; a second seal face member l8 associated in fixed rotational relationship and sealed with respect to a second component ll and a third seal face member 2l interposed between the first and second seal face members l2, l8. Spring means 20 is provided to urge the second seal face member l8 towards the first seal face member l2 and maintain the first, second and third seal face members l2, l8, 2l in sealing engagement. The sealing faces 22, 23, 24, 25 of the first, second and third seal face members l2, l8, 2l are inclined, so that the first and second seal face members l2 and l8 impose a radial load on the third seal face member 2l. Two such seal assemblies may be provided co-axially of one another to provide a double seal.

Description: The present invention relates to mechanical face seals. According to one aspect of the present invention a mechanical face seal for providing a fluid tight seal between a pair of relatively rotatable components comprises; a first annular seal face member mounted in fixed rotational relationship and sealed with respect to one of said components; a second annular seal face member mounted in fixed rotational relationship and sealed with respect to said other component, said second seal face member being moveable axially with respect to the two components; a third annular seal face member disposed between and free to rotate relative to the first and second seal face members; and spring means associated with the second seal face member to urge it axially towards the first seal face member, so as to maintain opposed sealing faces of the third seal face member in sealing engagement with sealing faces of the first and second seal face members respectively, characterised in that the sealing faces of the first, second and third seal face members are inclined so that the first and second seal face members impose a radial load on the third seal face member. The inclined sealing faces of the first and second seal face members will thus exert a radial force on the third seal face member, which will centralise the third seal face member and provide radial stability. Preferably the inclined sealing faces of the first and second seal face members will be oppositely inclined and exert an inward radial load on the third seal face member. Two such mechanical face seal assemblies may be mounted coaxially of one another to provide a double seal. Preferably in a double seal of such configuration the sealing faces of the first seal face members are oppositely inclined, the sealing faces of the second seal face members are oppositely inclined and each pair of sealing faces of the axially opposed first and second seal face members are oppositely inclined. The inner and outer first seal face members may be defined by a single annular component. However, each pair of second seal face members and each pair of third seal face members are preferably defined by separate annular components. Separate spring means may be provided to urge each of the second seal face members towards the opposed sealing faces of the first seal face members. With the double seal assembly disclosed above, a chamber is defined between the pair of the third seal face members, one or more passages passing between the concentric sealing faces of the first or second seal face members may be provided to this chamber, so that fluid leaking past the sealing faces may be drained from the chamber, or fluid may be introduced into the chamber to provide a barrier and for lubricating and/or cooling purposes. Several embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings, in which: Figure l shows in part section, a mechanical face seal formed in accordance with the present invention; Figure 2 shows in part section, a modified version of the seal shown in Figure l; and Figure 3 shows in sectional elevation a double seal formed in accordance with the present invention. Figure l illustrates a mechanical face seal which provides a seal between a housing l0 and a rotatable shaft ll at the point where the shaft ll penetrates the housing l0. A first annular seal face member, or seat l2, is located within a recess l3 in the housing l0, around the periphery of the bore through which the shaft ll passes. The seat l2 is sealed to the housing l0 by means of an elastomeric O-ring l4 or other conventional methods. A sleeve member l5 is mounted upon the shaft ll adjacent to but spaced axially from the housing l0 and is clamped thereto by clamping ring l6 carrying a plurality of radially disposed clamping screws (not shown). The sleeve l5 is sealed to the shaft ll by means of elastomeric O-ring l7. A second annular seal face member l8 is slidingly located on the sleeve l5 and is sealed thereto by means of elastomeric O-ring l9. A plurality of axially extending circumferentially spaced compression springs 20 acting between the clamping ring l6 and the seal face member l8 urge the seal face member l8 towards the seat l2. A pin, or similar driving device, not shown, engages in opposed bores in the second seal face member l8 and clamping ring l6 to locate the second seal face member l8 rotationally with respect to shaft ll. The seat l2 and second seal face member l8 are provided with opposed mutually inclined frustroconical sealing faces 24, 25. A third annular seal face member 2l is positioned between the sealing faces 24, 25 and has corresponding sealing faces 22, 23 which engage the sealing faces 24, 25 respectively and are maintained in sealing engagement therewith by means of the axial force exerted by springs 20. The frustroconical surfaces 24, 25 also exert an inwardly radial force on the third seal face member 2l, to centre it with respect to said surfaces. In the seal arrangement described above, the third seal face member 2l floats between the seat l2 and second seal face member l8 and is not constrained rotationally with respect to either the shaft ll or housing l0. Under normal sealing conditions the third seal face member 2l will tend to rotate with the second seal face member l8, due to the small amount of drag that will exist between faces 23 and 25. However, if for some reason, for example temporary dry running, friction between one pair of faces 22 and 24 or 23 and 25 became exceptionally high, then relative movement between that pair of faces would stop and the relative movement would occur at the other pair of faces, thus avoiding the excessive wear that would otherwise occur at the high friction surfaces. In the seal described above, the third seal face member 2l may constitute the wear element and would be made of a softer material than the seat l2 and the second seal face member l8. For example, the third seal face member 2l could be made from graphite, carbon or plastics material and the seat l2 and second seal face member l8 from metal or a sintered refractory material, for example alumina. The seal face member 2l may however be made of similar or harder material than the seat l2 and second seal face member l8. Moreover, replaceable wearing faces may be provided on the seat l2 to define sealing face 24 and/or on member l8 to define sealing face 25. In order to facilitate removal and replacement of the third seal face member 2l when worn, this member may conveniently be split axially into a plurality of arcuate portions. Member 2l could then be removed and replaced merely be retracting the second seal face member l8. The various arcuate portions forming the third seal face member 2l will be held together when the seal is assembled by the inward radial forces applied by the conical faces 24, 25 of the seat l2 and second seal face member l8. The seat l2 and second seal face member l8 may also be split axially to facilitate removal and replacement. With such constructions, the portions of seat l2 will be held together by the surrounding housing l0; alternatively these portions may be bolted together using tangential bolts. The portions of the second seal face member l8 may be bolted together using tangential bolts or a suitable clamping ring. Provided the sealing faces 22, 23, 24 and 25 are machined to a reasonable finish, lapping of the faces is not necessary and a running in period could provide a fluid tight seal between the faces. This arrangement will also accommodate variations in eccentrics introduced, for example, by shaft radial or seal housing misalignments. However, where it may be necessary to accommodate large misalignments and/or sealing is required from start up, the faces 22, 23, 24 and 25 may be made semi-spherical as illustrated in Figure 2. With this arrangement the axial alignment of the third seal face member 2l with respect to the seat l2 and second seal face member l8 may vary considerably, whilestill maintaining full sealing engagement. Also as illustrated in Figure 2, an emergency sealing face 26 may be provided on the second seal face member l8, so that when wear of the third seal face member 2l reaches a certain limit or the third seal face member 2l collapses, for example as a result of accidental damage, the emergency sealing face 26 will engage the seat l2 to provide an emergency seal. In the double seal illustrated in Figure 3, a first annular seal face assembly or seat ll2, is bolted to a radially extending flange ll3 on the shaft lll, by means of a plurality of angularly spaced bolts ll4. The seat ll2 is sealed to the flange ll3 by means of an elastomeric O-ring ll5 or by other conventional methods. The seat ll2 defines a pair of oppositely inclined frustroconical sealing faces ll6 and ll7. A tubular support member l20 is bolted to the housing ll0 by means of a plurality of angularly spaced bolts l2l passing through a flange portion l22, so that the tubular portion of support member l20 extends coaxially of the shaft lll towards the seat ll2. The flange portion l22 of support member l20 is sealed with respect to the housing ll0, by means of an elastomeric O-ring l23. A pair of coaxial sealing rings l24 and l25 are slidingly mounted on the internal and external surfaces respectively, of the tubular portion of support member l20. The rings l24 and l25 are sealed with respect to the support member l20 by means of elastomeric O-rings l26. Keys l27 mounted on the support member l20 engage in axially extending key-ways l28 in the sealing rings l24 and l25, so as to permit axial but prevent rotational movement of the rings l24 and l25 relative to the support member l20. A plurality of angularly spaced axially extending grooves l30 and l3l of part circular cross section, are provided in the outer surface of ring l24 and the inner surface of ring l25, so that when aligned, the grooves l30 and l3l will provide locations for a plurality of helical compression springs l32. The grooves l30 and l3l open to the surface of the rings l24 and l25 that engage the support member l20 and are closed at their other end, so that the springs l32 may act between the end of support member l20 and the closed end of the grooves l30 and l3l, to urge the rings l24 and l25 axially towards the seat ll2. Alternate grooves l30 in ring l24 and alternate grooves l3l in ring l25 are of increased length relative to the intermediate grooves, and the shorter grooves l30 on ring l24 are aligned with the longer grooves l3l on ring l25, so that adjacent springs l32 will act between the support member l20 and either the end of groove l30 in ring l24 or the end of groove l3l in ring l25. In this manner, rings l24 and l25 will be independently loaded towards the seat ll2. Oppositely inclined frustroconical sealing faces l35 and l36 are provided on the ends of rings l24 and l25 respectively, sealing face l35 being axially aligned and of opposite inclination to the sealing face l6 on seat ll2, and sealing face l36 being axially aligned and of opposite inclination to sealing face ll7 on seat ll2. A pair of third seal face members l40 and l4l are positioned between the sealing faces of seat ll2 and rings l24 and l25, seal face member l40 having a pair of frustroconical sealing faces l42 and l43 corresponding to and engaging sealing face ll6 of seat ll2 and sealing face l35 of ring l24, respectively. Similarly the seal face member l4l has a pair of frustroconical sealing faces l44 and l45 corresponding to and engaging sealing face ll7 of seat ll2 and sealing face l36 of ring l25, respectively. The sealing faces ll6 and l42, l43 and l35, ll7 and l44, and l45 and l36 are maintained in sealing engagement by means of the axial force exerted by springs l32. The frustroconical surfaces ll6 and l35, and ll7 and l36 also exert radial loads on the seal face members l40 and l4l respectively to centre these with respect to said frustroconical surfaces. As with the embodiments described with reference to Figures l and 2, in the seal arrangement described above, the third seal face members l40 and l4l float between the seat ll2 and rings l24 and l25 of the second seal face assembly and are not constrained rotationally with respect to either the shaft lll or housing ll0, thus avoiding the excessive wear when one pair of faces is subjected to high friction running conditions. An annular chamber l50 is defined between the seal face members l40 and l4l. One or more passages l5l may be provided through the tubular portion of support member l20 and through the housing ll0, to communicate with this chamber l50. Where, for example, the seal is to be used to separate one service on the outside of ring l25 and member l4l from another service on the inside of ring l24 and member l40, the passage l5l may serve to remove any fluid which leaks past sealing faces ll6 and l42, l43 and l35, ll7 and l44 or l45 and l36, so that the fluid in one service will not be contaminated by the fluid in the other service, even if some leakage does occur across the sealing faces. Alternatively, if for example the seal is to be used to seal a potentially hazardous gas or vapour from atmosphere, the chamber l50 may be filled with a barrier liquid, which will also serve to lubricate and cool the sealing faces. As described with reference to Figures l and 2 the materials used to produce the members ll2, l24, l25, l40 and l4l may be selected for their wear properties or may be provided with wear inserts. The various annular members may be of split configuration to facilitate removal and replacement and the sealing faces may be of semi-spherical rather than frustro-conical configuration. Various modifications may be made, without departing from the present invention. For example the seat l2; 1l2 may be mounted with respect to the housing l0 and the members l8; l24 and l25 mounted with respect to the shaft ll; 1ll. Moreover the members l2; 1l2 may also be moveable axially with respect to the components. Furthermore, in the double seal, the sealing faces ll6 and ll7 of the seat ll2 may be formed on separate rings. While in the embodiment illustrated in Figure 3, rings l24 and l25 are of similar configuration, the configuration of these rings may be varied to adjust their pressure balance and hence the effect of the pressure of fluid on the inner and outer seals, so, that differential loading of the inner and outer seal face members may be achieved or to compensate for pressure differentials across the seal. Also the spring rates of the springs l32 acting on the rings l24 and l25 may differ to vary the axial loads applied to the inner and outer seal face members l40 and l4l.

Claims: 1. A mechanical face seal for providing a fluid tight seal between a pair of relatively rotatable components comprising; a first annular seal face member (l2; 1l2) mounted in fixed rotational relationship and sealed with respect to one of said components (l0; 1ll);a second annular seal face member (l8; 124, l25) mounted in fixed rotational relationship and sealed with respect to said other component (ll; 1l0), said second seal face member (l8; 124, l25) being moveable axially with respect to the two components, (l0, ll; 1l0, lll); a third annular seal face member (2l; 140, l4l) disposed between and free to rotate relative to the first and second seal face members (l2, l8; 1l2, l24, l25); and spring means (20; 132) associated with the second seal face member (l8; 124, l25) to urge it axially towards the first seal face member (l2; ll2), so as to maintain opposed sealing faces (22, 23; 142, l43, l44, l45) of the third seal face member (2l; 140, l4l) in sealing engagement with sealing faces (24, 25; 1l6, ll7, l35, l36) of the first and second seal face members (l2, l8; 1l2, l24, l25) respectively, characterised in that the sealing faces (22, 23, 24, 25; 142, l43, l44, l45, ll6, ll7, l35, l36) of the first, second and third seal face members (l2, l8, 2l; 1l2, l24, l25, l40, l4l) are inclined so that the first and second seal face members (l2, l8; ll2, l24, l25) impose a radial load on the third seal face member (2l; 140, l4l). 2. A mechanical face seal according to Claim l characterised in that the inclined faces (24, 25; 1l7, l36) of the first and second seal face members (l2, l8; 1l2, l25) exert an inward radial force on the third seal face member (2l; 14l). 3. A mechanical face seal characterised in that a pair of seal assemblies as claimed in Claim l or 2 are mounted coaxially of one another. 4. A mechanical face seal according to Claim 3 characterised in that a first seal face assembly (ll2) defines a pair of oppositely inclined sealing faces (ll6, ll7), a second seal face assembly (l20, l24, l25) defines a pair of oppositely inclined sealing faces (l35, l36), each pair of axially opposed sealing faces (ll6, l35 and ll7, l36) of the first and second seal face assemblies (ll2, l20, l24, l25) being oppositely inclined. 5. A mechanical face seal according to Claim 4 characterised in that the first seal face assembly (ll2) comprises a ring having a pair of inclined concentric annular sealing faces (ll6, ll7). 6. A mechanical face seal according to Claim 4 or 5 characterised in that the sealing faces (l35, l36) of the second seal face assembly (l20, l24, l25) and the third seal face members (l40, l4l) are defined by separate concentric seal face members (l24, l25, l40, l4l). 7. A mechanical face seal according to Claim 6 characterised in that the seal face members (l24, l25) of the second seal face assembly are slidingly mounted and sealed with respect to the internal and external diameters of a tubular support member (l20). 8. A mechanical face seal according to Claim 5 characterised in that keys (l27) mounted on the tubular support member (l20) engage in axially extending key-ways (l28) in the seal face members (l24, l25) of the second seal face assembly to prevent rotation of said seal face members (l24, l25) relative to the support member (l20) while permitting axial movement of the seal face members (l24, l25). 9. A mechanical face seal according to any one of Claims 6 to 8 characterised in that separate spring means (l32) are provided to urge the seal face members (l24, l25) of the second seal face assembly independently towards the first seal face assembly (ll2). l0. A mechanical face seal according to Claim 9 characterised in that a plurality of angularly spaced axially extending grooves (l30, l3l) are provided in the outer surface of the inner seal face member (l24) of the second seal face assembly and the inner surface of the outer seal face member (l25) of the second seal face assembly, so that when aligned, the grooves (l30, l3l) will provide locations for a plurality of angularly spaced compression springs (l32) which will act between the end of the tubular support member (l20) and the closed end of the axially extending grooves (l30, l3l), to urge the seal face members (l24, l25) of the second seal face assembly towards the first seal face assembly (ll2). 11. A mechanical face seal according to Claim l0 characterised in that alternate axially extending grooves (l3l) in the outer seal face member (l25) of the second seal face assembly and alternate axially extending grooves (l30) in the inner seal face member (l24) of the second seal face assembly are of increased length relative to the intermediate grooves, the shorter grooves (l3l) on the outer seal face member (l25) being aligned with the longer grooves (l30) on the inner seal face member (l24) so that adjacent springs (l32) will act between the support member (l20) and the end of the shorter groove (l3l) in the outer seal face member (l25) or the shorter groove (l30) in the inner seal face member (l24). 12. A mechanical face seal according to any one of Claims 9 to ll characterised in that the spring rate of the spring means (l32) acting upon the inner and outer seal face members (l24, l25) of the second seal face assembly differ. 13. A mechanical face seal according to any one of Claims 4 to l2 characterised in that the dimensions of the concentric seal face members (l24, l25) of the second seal face assembly differ, so that the pressure balance of the seal face members differ (l24, l25) . 14. A mechanical face seal according to any one of Claims 3 to l3 characterised in that an annular chamber (l50) is defined between the third seal face members (l40, l4l), a passage (l5l) being provided to said annular chamber between the sealing faces (ll6, ll7 or l35, l36) of the first or second seal face members (ll2, l24, l25) by means of which fluid may be removed from or introduced into the annular chamber (l50). 15. A mechanical face seal according to any one of the preceding claims characterised in that the or each third seal face member (2l; 140, l4l) is made of material which is softer than the materials used to define the sealing faces of the first and second seal face members (l2, l8; ll2, l24, l25). 16. A mechanical face seal according to Claim l5 characterised in that the or each third seal face member (2l; 140, l4l) is made from graphite, carbon or a plastics material and the first and second seal face members (l2, l8; 1l2, l24, l25) are made from metal or a sintered refractory material. 17. A mechanical face seal according to any one of the preceding claims characterised in that the sealing faces (24, 25; 1l6, ll7, l35, l36) of the first and second seal face members (l2, l8; 1l2, l24, l25) are defined by replaceable inserts. 18. A mechanical face seal according to any one of the preceding claims characterised in that one or more of the annular members (l2, l8, 2l; 1l2, l24, l25, l40, l4l) are split axially into a plurality of arcuate portions. 19. A mechanical face seal according to any one of the preceding claims characterised in that the sealing faces (22, 23, 24, 25; 1l6, ll7, l35, l36, l42, l43, l44, l45) of the seal face members (l2, l8, 2l; 1l2, l24, l25, l40, l4l) are of frustroconical configuration. 20. A mechanical face seal according to any one of Claims l to l8 in which the sealing faces (22, 23, 24, 25) of the seal face members (l2, l8, 2l) are of semi-spherical configuration 2l. A mechanial face seal according to any one of the preceding claims in which an emergency sealing face (26) is provided on the second seal face member (l8) for engagement with the first seal face member (l2) when wear on the third seal face member (2l) reaches a certain limit or the third seal face member (2l) collapses.

Inventors: KEMP, JOHN, LOWE, DAVID JAMES
Applicants: JOHN CRANE UK LIMITED
Application year: 1986
Main classification: F16J15
IPC codes: F16J15