Abstract:
A mechanical shaft seal includes stationary and rotary assemblies providing mating seating faces  3, 11  such that first and second fluids are kept separate from each other. A barrier fluid system provides a third fluid between the first and second fluids and a flow inducer  13  promotes axial flow of the barrier fluid in the desired direction irrespective of the direction of rotation of the rotary assembly.

Description:
FIELD OF INVENTION 
     This invention relates to mechanical seals which may be used to separate a first liquid fluid from a second fluid. In the context of a pump, for example, the mechanical seal is mounted so as to extend between the pump shaft and the pump housing. 
     BACKGROUND OF THE INVENTION 
     A mechanical shaft seal for separating a first liquid fluid from a second fluid includes a rotary assembly for mounting on a rotatable shaft for rotation therewith and a stationary assembly for securing to a fixed structure within which the rotary assembly is located. Such a seal includes a “floating component” which forms part of either the rotary or the stationary assembly and which is axially moveable relative to the rotatable shaft. In addition, the seal includes a “static” component which forms part of the other of the rotary and stationary assemblies, this component being axially fixed relative to the rotatable shaft. The floating component has a flat angular end face or seal face which is directed toward the static component, usually by means of one or more springs, to close the seal faces together to form a sliding face seal. 
     A seal with a floating component forming part of the rotary assembly is described as a rotary seal and a seal whose floating component forms part of the stationary assembly is referred to as a stationary seal. 
     If the sliding seal between the rotary and stationary components is assembled and pre-set prior to despatch from the manufacturer, the seal is referred to as a “cartridge seal”. If the rotary and stationary components are despatched in unassembled form from the manufacturer, the seal is a “component seal”. 
     A mechanical seal may be single mechanical seal or a multiple mechanical seal, typically a double or triple mechanical seal. Furthermore a mechanical seal may include a barrier fluid system by means of which a third fluid, normally liquid, is fed to the seal and this third or barrier fluid acts to separate the first and second fluids and is intended to facilitate the removal of heat generated between the sliding seal faces, thereby helping to prolong the life of the seal. 
     In order for the barrier fluid system to be effective, the barrier fluid has to be fed to the seal and, within the seal, to one or more areas where cooling is to be effected and thence is fed away from the seal. This involves axial movement of the barrier fluid and to some extent this is affected by the forces induced as a result of the rotation of the rotary assembly relative to the stationary assembly. 
     STATEMENTS OF THE INVENTION 
     The present invention is based on the discovery that there may be located within the seal a means for promoting or enhancing the actual movement of the barrier fluid along a desired flow path, which means may be effective regardless of the direction of rotation of the rotary assembly relative to the stationary assembly. 
     According to the present invention there is provided a mechanical shaft seal for separating a first liquid fluid from a second fluid comprising: 
     (a) a rotary assembly for mounting on rotatable shaft for rotation therewith: 
     (b) a stationary assembly for securing to a fixed structure within which the rotary assembly is located; 
     (c) said rotary assembly and said stationary assembly each carrying a respective mating sealing face; 
     (d) one of said seal faces being located on a floating component mounted for axial movement with respect to said shaft; 
     (e) means for urging the floating component in a direction toward the other of said seal faces; 
     (f) means for feeding a third fluid to a location within the seal which, when the seal is in use, lies between the first and second fluids; and 
     (g) means for promoting axial flow of said third liquid within the seal, said axial flow promoting means being arranged to promote said flow irrespective of the direction of rotation of the rotating assembly relative to the stationary assembly. 
     Preferably the axial flow promotion means comprises a member having a grooved, circumferentially extending face, at least one groove extending both axially and circumferentially in one direction about said face and at least one other groove extending both axially and circumferentially in the opposite direction about said face. 
     Accordingly the present invention provides the inducement of barrier fluid flow which is independent of the direction of rotation of the equipment of which the seal forms a part. 
     Preferably the grooves have a plan view angle relative to the longitudinal axis of the seal of between 1° and 89°. 
     The base of at least one of the grooves may be inclined radially relative to the longitudinal axis of the seal. Additionally or alternatively, the face of the grooved member, between at least two grooves, may be inclined relative to the longitudinal axis of the seal. 
     The grooves may be circumferentially adjacent each other on the grooved member. Alternatively, at least one groove may be axially adjacent or separated from at least one other groove. 
     The groove member may form part of the rotary assembly. The fixed structure to which, in use, the stationary assembly is secured will include a housing having a component located radially outside grooved member, said component having an inner face which is inclined relative to the longitudinal axis of the seal. 
     Alternatively, the grooved member may form part of the stationary assembly or, in use, form part of the fixed structure to which the stationary assembly is attached. 
     Preferably the seal defines a space to which, in use, the third fluid is fed, there being located within said space means for dividing said space into two opposing flow paths for said third fluid. 
     The present invention may be applied to rotary and stationary seals whether they are of cartridge or component type. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are as follows: 
     FIG. 1 is a longitudinal section through a double stationary mechanical seal in accordance with the present invention; 
     FIG. 2 is a longitudinal section of part of a seal similar to that shown in FIG. 1; 
     FIG. 3 is a perspective view of the axial flow promoting member of the seal shown in FIG. 2; 
     FIG. 4 is an extrapolated plan view of the grooved face of the member shown in FIG. 3; 
     FIGS. 5 a  to  5   d  are extrapolated plan views of alternative groove patterns; 
     FIG. 6 is a longitudinal section of part of a second embodiment of a seal in accordance with the present invention; 
     FIG. 7 is a longitudinal section of part of a third embodiment of a seal in accordance with the present invention; 
     FIG. 8 is an extrapolated plan view of the grooved face of the axial flow promoting member of the seal of FIG. 7; 
     FIG. 9 is a longitudinal section through a fourth embodiment of a seal in accordance with the present invention; 
     FIG. 10 is a longitudinal cross section of part of a fifth embodiment of a seal in accordance with the present invention; 
     FIG. 11 is a longitudinal section through part of a seventh embodiment of a seal in accordance with the present invention; 
     FIGS. 12 a  to  12   c  illustrate different groove profiles of flow promoting members which may be used in seals for the present invention; 
     FIG. 13 is a longitudinal section of part of a seventh embodiment of a seal in accordance with the present invention; and 
     FIG. 14 is a longitudinal section of part of an eighth embodiment of a seal in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described, by way of examples only, with reference to the accompanying drawings. 
     Referring to FIG. 1 of the accompanying drawings, there is illustrated a double stationary mechanical seal located about a rotatable shaft  6 . The seal is a cartridge seal and includes on the inboard side of the seal a stationary component  1  and, a rotary component  2  which together define sealing faces  3 . Rotary component  2  is located radially outwardly of a sleeve  5  which is fixed for rotation with shaft  6 . 
     As well as the inboard sealing components mentioned above, the seal includes an outboard sealing arrangement providing scaling faces  11 . Barrier fluid is fed to the seal via inlet  9  located in gland  10 . The barrier fluid follows a path located radially outwardly of a deflector ring  7  in a direction towards seal face  3 , this path being indicated by the arrows in the upper part of FIG.  1 . The barrier fluid then follows a path located radially inwardly of deflector  7  as indicated by the arrows in the lower part of FIG.  1 . The barrier fluid exits from the seal via outlet  12  located in gland  10 . The barrier fluid may then be recycled back to inlet  9 . 
     Flow inducing ring  13  is located between the inboard sealing faces  3  and the outboard sealing faces  11 . At best seen in FIGS. 2 and 3, ring  13  includes a main body portion  131  from the inner edge of which extends an integral channel  132  housing an O ring  133 . O ring  133  bears against sleeve  5 . 
     Extending in an outboard direction from main body portion  131  of ring  13  is a flange  134  which steps outwardly to provide a space between this flange and the rotary component  135  of the outboard seal. Located in this space is a further O ring  136 . Accordingly the flange inducer ring forms part of the rotary assembly with which it is in sealing engagement through rings  133  and  136 . 
     Extending into main body portion  131  of ring  13  from the outer face thereof is a plurality of deep grooves, slots or vanes  15 , each of which extend from the inboard face of main body portion  131  to the outboard face thereof. Each groove  15  is rectangular in cross section and extends not only axially but also circumferentially across the main body portion  131  of ring  13 . Some of the grooves extend circumferentially in one direction and others in the opposite direction. The resulting pattern of grooves is best seen in FIG. 4 from which it will be seen that some grooves  137  are single grooves and others  138  are double grooves due to the meeting of two single grooves where they converge on the inboard or outboard edge of body portion  131 . The resulting pattern is one of alternating double and single grooves, the double grooves being of chevron shape in plan. 
     The grooves  15  and  16 , located on ring  13 , rotate with the seal and cause the barrier fluid to be propelled axially in an outboard direction. When the shaft  6  is rotating in one direction, then grooves  15  are effective to cause the barrier fluid flow and when the shaft rotates in the opposite direction, grooves  16  are effective to cause barrier fluid flow in the same outboard direction. Accordingly barrier fluid flow is achieved irrespective of the direction of the rotation of flow inducing ring with the shaft. 
     FIGS. 5 a  to  5   d  illustrate different groove patterns that are effective to produce barrier fluid flow in the desired direction irrespective of the direction of rotation of the shaft. It will been seen that in each of these groove patterns there are some grooves which extend in one direction circumferentially and others in the opposite direction. The pattern of grooves as well as the shape of each groove may be varied to suit the performance required from the flow inducing ring. 
     Referring to FIG. 6 of the accompanying drawings, there is illustrated a second embodiment of a seal in accordance with the present invention. This seal is substantially similar to that shown in FIG.  1 . However, in this case ring  61 , which corresponds to ring  13  of the FIG. 1 embodiment is not provided with the grooves  15  and  16 . Instead the housing  25  is provided with grooves  62  which extend radially outwardly from the inner face of the housing adjacent ring  61 . The pattern of grooves is similar to that shown in FIG.  4 . 
     The grooves  15  and  16  in the ring  13  make an angle of about 30° from the longitudinal axis. As illustrated in FIGS. 5 a  to  5   d , the grooves may make other angles and indeed the angle may vary from 1° to 89°, typically from 5° to 85°. 
     Referring to FIG. 7 of the accompanying drawings, a third embodiment of a seal in accordance with the present invention is broadly similar to that illustrated in FIG.  1 . The flow inducing ring  73  is provided, however, with two sets of grooves, inboard set  19  and outboard set  20 , the two sets being located axially adjacent each other in a tandem arrangement. The inboard set  19  is provided with grooves  21  (see FIG. 8) which produce barrier flow when the shaft rotates in a clockwise direction. The outboard  20  has grooves  22  which produce a barrier flow when the shaft rotates in an anti-clockwise direction. 
     It will be appreciated that the inboard and outboard sets of grooves could be interchanged. Also the number of sets of grooves, and the orientation of the grooves within each set, can be varied to produce any desired amount of barrier fluid flow. Furthermore the sets of grooves may be placed on the inner surface of the housing  74  as shown in FIG. 9 representing a fourth embodiment of the present invention. 
     Referring to FIG. 10 of the accompanying drawings, a fifth embodiment of a seal in accordance with the present invention is broadly similar to that shown in FIG.  1 . However in this case the flow inducing ring  83  is provided with grooves  84 , each of which has an inclined base  87 , the inclination being in an outward direction from the inboard to the outboard side of the seal. 
     Referring to FIG. 11 of the accompanying drawings, a sixth embodiment of a seal in accordance with the present invention is again similar to that illustrated in FIG.  1 . However, in this case the flow inducing ring  93  has an inclined outside diameter  98 , the inclination again being outwardly from the inboard to the outboard side of the seal. 
     Referring to FIGS. 12 to  12   c  of the accompanying drawings, there are illustrated different groove cross-sections which may be used in, for instance, the flow inducing ring  13  of the FIG. 1 embodiment. In FIG. 12 a , the groove  15  has a cross-section similar to that shown in FIG.  3 . The groove in cross-section has a base which is curved to follow the circumferential surface of the ring at that diameter. The sides of the groove extend radially outwardly from the base. 
     The groove  15  shown in FIG. 12 b  is gently curved from the centre of its base where it follows the circumference at that diameter, the curve changing direction to provide the curved sides of the groove extending to the outer surface of the ring. In FIG. 12 c  the grooves  15  are also curved but much more sharply at the sides of the groove so that each side is channel-shaped. 
     Referring to FIG. 13 of the accompanying drawings, a seventh embodiment of a seal in accordance with the present invention is broadly similar to that shown in FIG.  1 . However, in this case the inner radial surface  96  of housing  97  is inclined in a direction outwardly from the inboard to the outboard side of the seal. Furthermore, the outer radial surface of flow inducing ring  93  is also inclined in the same direction to provide a gap between housing  97  and ring  93  which is constant from the inboard to the outboard side. 
     Where the inner radial surface of the housing and/or the outer radial surface of the flow inducing ring is inclined, the angle of inclination may vary from 1° to 89°. 
     Referring to FIG. 14 of the accompanying drawings, there is illustrated an eighth embodiment of a seal in accordance with the present invention, the seal being again broadly as shown in FIG.  1 . In this case the inner radial surface  126  of housing  127  is inclined in a direction outwardly from the inboard to the outboard side of the seal. The outer radial surface  128  of flow inducing ring  113  is parallel to the longitudinal axis of the seal so that the gap between the two adjacent radial surfaces increases from the inboard to the outboard side of the seal. 
     It should be appreciated that the present invention may be applied to a seal to be provided between a stationary shaft and a rotatable housing. 
     It should also be appreciated that the flow inducing means may be located anywhere in the flowpath of the barrier fluid. For instance, in another embodiment in accordance with the present invention, the flow inducing means may be integral with the sleeve (item  5  of the FIG. 1 embodiment) and may be positioned below a deflector (item  7 A of FIG. 1) which in turn extends below the inboard sealing faces.