Abstract:
A rotary seal has a floating seal face in a sealing relationship with a stationary seal face, and a fluid collection cavity adjacent the floating seal face and the stationary seal face. The seal further includes a device for introducing a lubricant into the vicinity of the fluid collection cavity and a device for promoting coalescence of the lubricant, so that the lubricant accumulates in the fluid collection cavity and lubricates the seal faces.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to rotary seals and is concerned with their use in rotating equipment and especially devices which prevent the ingress of a fluid or solid to an area which results in deterioration of equipment life. Such devices are often referred to as bearing protectors or bearing isolators. However, the use of such rotary seals extends well beyond the protection of a bearing in rotating equipment. Accordingly, while reference will be made below to bearing protectors, it should be understood that this term is used, as far as the invention is concerned, in connection with mechanical and other seals having wider uses. 
       BACKGROUND TO THE INVENTION 
       [0002]    The purpose of a bearing protector is to prevent the ingress of fluid, solids and/or debris entering a bearing arrangement and thereby prevent the failure of the bearing. Bearing protectors generally fall into two categories: repeller or labyrinth bearing protectors; and mechanical seal bearing protectors. 
         [0003]    A repeller bearing protector includes a component which is mounted for rotation about a shaft and axially fixed in relation thereto. For example, the shaft may be that of a pump or other piece of rotating equipment. The protector includes a static component which is also axially fixed and is butted or secured to the stationary part of the equipment. 
         [0004]    The rotating component typically has a complex outer profile which is located adjacent to an inner complex profile of the stationary component. Together these complex profiles provide a tortuous path preventing the passage of the unwanted materials. 
         [0005]    A repeller bearing protector normally works only during the operation of the equipment. When the equipment is static, the complex labyrinth design is unable to hold a fluid level which, in horizontal application, is at a higher radial level than the inlet position of the protector. 
         [0006]    Mechanical seals are used in all types of industries to seal a variety of different process media and operating conditions. A mechanical seal bearing protector overcomes the static limitations of the labyrinth design by the use of two opposing seal faces. Such a protector includes a “floating” component which is mounted for axial movement about the rotary shaft of, for example, a pump and a “static” component which is axially fixed and is typically secured to a housing. The floating component has a flat annular end seal face which is directed towards a corresponding seal face of the static component. The floating component is urged towards the static component to close the seal faces together to form a sliding face seal, usually by means of one or more spring members. The rotating component, which in practice could be either the floating or the static component, is referred to as the rotary component. The other component does not rotate and is referred to as the stationary component. A rotary seal is one whose floating component is rotary and, in a stationary seal, the floating component is stationary. If the sliding seal between the rotary and the stationary components is assembled and pre-set to despatch from the manufacturer, the seal is termed a “cartridge seal”. If the rotary and the stationary components are despatched in unassembled condition by the manufacturer, the seal is termed a “component seal”. The term “inboard” defines the area adjacent to the process media and the term “outboard” defines the area adjacent the atmospheric side. 
         [0007]    Desirably, a mechanical seal bearing protector prevents the ingress of fluid etc. irrespective of the direction of shaft rotation. 
         [0008]    Bearing protectors are generally very compact at least as far as their axial length is concerned. Typically they are used to replace so-called lip seals and are fitted into spaces previously occupied by such seals. In order to maintain a compact axial length, the floating component may be energised by one or more magnets in either attracting mode (U.S. Pat. No. 5,078,411 Geco) or repelling mode (EP 0105616 Burles). 
         [0009]    Furthermore, our co-pending patent application (PCT/GB03/02941 Roddis) defines a dual mechanical seal bearing protector, whereby two independent stator seal faces are attracted to a common rotor seal face by one or more magnets. 
         [0010]    The major benefit of mechanical seal bearing protectors is that they provide a hermetic sealing solution. This means that they prevent the ingress or egress of fluid. However, all contacting mechanical seal bearing protectors operate on a fluid film between the counter rotating seal faces. In marginal lubrication applications the fluid film is typically very thin which may cause heat generation and/or seal face deterioration. Seal face deterioration will lead to loss of the hermetic seal. 
         [0011]    There is an increasing trend for industry to adopt oil-misting techniques to lubricate their bearing arrangements in rotating equipment. Oil misting involves a separate supply unit, which is connected, supply and return, to the bearing cavity of the rotating equipment. Said supply unit provides an oil mist at a velocity in the order of 0.3 cc/hr for a 1.000″/25 mm bearing bore (Page 25—Oil Mist lubrication, Bloch &amp; Shamin 1998). However 0.3 cc/hr velocity is insufficient to adequately lubricate and cool a mechanical seal face and therefore a conventional mechanical seal face bearing protection solution may fail to function correctly under such conditions. 
         [0012]    Unfortunately, a non-contacting bearing protector, by its nature, has an oil mist escape path between the counter rotating components. This leads to oil mist being evacuated into the environment. Not only does this lead to loss of oil and therefore significantly increases the running cost of the supply unit, in many parts of the world, the environmental issues are unacceptable. 
         [0013]    It is therefore highly desirable to provide a hermetic mechanical seal bearing protector, which can operate in a minimal lubrication condition, as typically found in oil mist applications. 
       STATEMENTS OF THE INVENTION 
       [0014]    According to the present invention there is provided a rotary seal having a floating seal face in sealing relationship with a stationary seal face, a fluid collection cavity adjacent said seal faces, means for introducing a lubricant into the vicinity of said cavity, means for promoting the coalescence of said lubricant whereby said lubricant accumulates in said cavity and lubricates said seal faces. 
         [0015]    The promoting means may be, for instance, at least one of a textured seal face surface, one or more grooves or slots and a pumping element. Accordingly, the cavity is in fluid communication with said seal faces. 
         [0016]    The seal may be in the form of, for instance, a mechanical seal or other type of bearing protector. 
         [0017]    The lubricant introducing means may be, for instance, an inlet port provided in the seal body or an item to which the seal is, in use, attached. In use a device for creating an oil mist may be attached to such an inlet. 
         [0018]    The lubricant is typically one providing insufficient lubrication to the seal faces. For instance, it may be provided in the form of an oil mist or other “marginal” lubricating fluid. By “marginal” is meant a lubricant which is insufficiently present without coalescence to increase the amount of lubricant per unit volume in contact with the seal faces. 
         [0019]    Preferably, said seal faces are respectively floating and stationary with respect to the longitudinal axis of the seal. 
         [0020]    The rotary seal may be, for instance, a hermetic seal or a repeller bearing protector and may be in the form of a mechanical seal. 
         [0021]    Preferably, said floating seal face is urged by a magnetic biasing means towards said stationary seal face. Although reference is made to a magnetic biasing means, it should be understood that such magnetic means may be replaced either wholly or partially by another biasing member, for instance, some form of spring or resilient elastomeric member, including a bellows-like arrangement. 
         [0022]    Preferably, said floating seal face and said magnetic biasing means are rotationally fixed relative to each other and said stationary seal face is free to rotate relative to said floating seal face. 
         [0023]    Preferably, the seal includes two pairs of sealing faces. Preferably, at least one seal face is textured and preferably, the textured seal face is the face adjacent to the primary sealed fluid which may be an oil mist. Preferably, the textured seal face is textured from the innermost radial part of the seal face to the outermost part of the seal face. Preferably, the sealed fluid is able to pass between the seal faces and thereby accumulate in a radial cavity adjacent to the hermetic seal face. By “textured” it is meant that a seal face has ridges, grooves or other structure such that channels are provided between the said seal face and its opposed seal face. 
         [0024]    Accordingly, it is preferred that, adjacent to the hermetic seal face, there is a radially and/or longitudinally extending cavity which captures and retains coalesced oil from the oil mist. In effect, the function of the textured seal face is to promote the coalescence of the oil mist by energising the fluid so that it can be put into communication with the hermetic seal face. 
         [0025]    Other coalescence promoters may be used. For instance, an engraved seal face or a suitable labyrinth arrangement may be employed. Essentially, any arrangement which promotes oil mist coalescence and then the retention of the coalesced fluid adjacent to a hermetic seal face, which prevents it from entering the bearing cavity, may be used in the present invention. 
         [0026]    Preferably, one or more magnets are arranged within the seal such that, in use, the magnets are non-rotating and thus mounted in a non-rotating housing. Alternatively, one or more rotating magnets may be used, these being mounted in a rotating element which is either longitudinally floating or longitudinally static. 
         [0027]    Preferably, the magnet or magnets are mounted radially outwards of the seal face. A radial support may be provided to both support and circumferentially space apart a plurality of magnets. 
         [0028]    A seal of the present invention preferably includes a housing which has at least one radially outwardly positioned equipment chamber location feature. Such a feature is located adjacent to a radially extending groove which contains at least one elastomeric member for sealing the housing to the equipment chamber. The arrangement may be provided with at least two radially outwardly positioned equipment chamber location features, with correspondingly at least two radially extending grooves. Both of the grooves contain at least one elastomeric member for sealing the housing to the equipment chamber. Preferably the two location features are radially and/or longitudinally displaced relative to each other. 
         [0029]    The seal may include a housing which is provided with a radially extending hole connecting the outermost and innermost surfaces of the housing. 
         [0030]    At least one of the seal faces in a seal of the invention may be segmented. The seal may include two substantially identical pairs of contacting seal faces which may be in modular form. 
         [0031]    A rotating member of the seal of the invention may include at least one non-continuous, circumferentially and radially extending portion. 
         [0032]    Preferably, a seal of the invention may include at least one magnetic member which is radially and axially restrained in the housing by a housing groove, said groove preferably incorporated at least one inwardly radially extending indentation adjacent to a magnet to provide circumferential anti-rotation of said magnet in said groove. 
         [0033]    A seal of the invention may include at least one seal face holder, said seal face holder having magnetic attraction properties. A mechanical seal of the invention may contain at least two seal faces, axially restrained in a housing, the first seal face having the ability to rotate with a shaft or other item of rotating equipment, and the second seal face being non-rotatable with respect to the housing of the rotation equipment. Either the rotating seal face and/or the stationary seal face may be housed and/or secured, permanent or otherwise, in a seal face holder. 
         [0034]    A mechanical seal of the invention may have at least three seal faces, preferably, but not essentially, longitudinally restrained in a housing. The first seal face may have the ability to rotate with a shaft or other item of rotating equipment and the second and third seal faces may be non-rotatable with respect to the housing of the rotating equipment. Equally, said three seal faces may include two seal faces having the ability to rotate with a shaft or other item of rotating equipment and the third seal face being non-rotatable with respect to the housing of the rotating equipment. 
         [0035]    Embodiments of mechanical seals in accordance with the present invention may be such that at least one rotary member and/or one stationary member can be mechanically attached to the items of rotary equipment. 
         [0036]    A seal of the invention may include a housing having at least one longitudinal through hole or slot for accommodating a stud or bolt in an item of rotating equipment, thereby allowing the housing of the mechanical seal to be secured to the rotating equipment. 
         [0037]    Preferably, a seal of the invention includes at least two counter opposed magnetic members, said first magnetic member attracting a first axially floating seal face and a second magnetic member attracting a second axially floating seal face. 
         [0038]    Preferably, a seal of the invention includes lubrication means for feeding lubricant to the contacting seal faces. A cavity may be provided between at least two sets of sliding surfaces and said cavity may be connected to the lubrication means which acts automatically to fill the cavity with lubrication fluid. 
         [0039]    A seal of the invention may be a double mechanical seal of a size small enough to fit in a space having a radial cross section as small as 1.5 mm, but preferably larger. A double mechanical seal in accordance with the present invention may be small enough to fit in a space having a longitudinal dimension as small as 6 mm but preferably larger. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0040]    The accompanying drawings are as follows: 
           [0041]      FIG. 1  is a longitudinal cross-section through an item of rotating equipment with an oil mist system connected to the bearing chamber; 
           [0042]      FIG. 2A  is a longitudinal cross-section of the first embodiment of the invention, showing one textured seal face adjacent to the sealed fluid; 
           [0043]      FIG. 2B  corresponds to  FIG. 2A  and shows an end view through the centre of the rotary seal face on line A-A of the first embodiment; 
           [0044]      FIG. 2C  corresponds to  FIG. 2A  and is an enlarged partial longitudinal section of the textured seal face of the first embodiment; 
           [0045]      FIG. 3  corresponds to  FIG. 2A  and shows the end view of the textured seal face only on line B-B of the first embodiment; 
           [0046]      FIG. 4  is a partial longitudinal cross-section of a second embodiment of the invention, showing one textured seal face adjacent to the atmospheric side; 
           [0047]      FIG. 5  corresponds to  FIG. 2B  and shows the end view of the textured seal face, on line B-B of the third embodiment, with a radial cavity adjacent to the hermetic seal face; 
           [0048]      FIG. 6  is a partial longitudinal cross-section of a fourth embodiment of the invention, showing two textured seal faces; 
           [0049]      FIG. 7A  shows an alternative end view of a textured seal face on line E-E of  FIG. 6   
           [0050]      FIG. 7B  shows an alternative end view of a partially textured seal face on line D-D of  FIG. 6 ; 
           [0051]      FIG. 8  is a partial longitudinal section through a fifth embodiment of the invention which is a bearing protector of the invention, showing a combined labyrinth seal and hermetic seal; 
           [0052]      FIG. 9  is a partial longitudinal section through a sixth embodiment of the invention which is an item of rotating equipment with an oil mist system connected to the radial cavity between the textured and hermetic seal faces; 
           [0053]      FIG. 10  is a longitudinal section through a seventh embodiment of the invention, showing a concentric pair of seal faces, with one textured seal face adjacent to the sealed fluid; and 
           [0054]      FIG. 11  corresponds to  FIG. 10  and shows the end view on line C-C of the seventh embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0055]    The invention will now be described, by way of examples only, with reference to the accompanying drawings. 
         [0056]    In general, rotary seals in accordance with the present invention may be used not only in the case where the shaft is a rotary member and the housing is a stationary member but also the reverse situation, that is to say, in which the shaft is stationary and the housing is rotary. 
         [0057]    Furthermore, the invention may be embodied in both rotary and stationary arrangements, that is to say, the axially floating face or faces may be either rotary or stationary. 
         [0058]    The invention may also be embodied in cartridge and component seal formats with metallic components as well as non-metallic components in both single and double seal formats. Double seal formats include tandem, face-to-face or back-to-back orientations in a series or concentric arrangement. 
         [0059]    Referring to  FIG. 1  of the accompanying drawings, there is illustrated a longitudinal cross-section through an item of rotating equipment  10  with an oil mist system  11  connected to the bearing chamber  12 . One side of the bearing chamber  12  incorporates a traditional non-contacting bearing protector such as a labyrinth seal  13  and the other side incorporates a single mechanical seal  14 . 
         [0060]    The oil mist is supplied through the feed pipe  16  from the oil mist system  11  to the bearing cavity  17  via inlet  15 . The non-contacting labyrinth seal  13  allows the oil mist to exit the bearing cavity  17  to the atmosphere  18 A. This is considered to be environmentally unacceptable. The single mechanical seal  14  has insufficient lubrication from the oil mist to be able to function correctly and thus is prone to overheating and seal face deterioration—eventually leaking oil mist to the atmosphere  18 B. 
         [0061]    Reference here is made to our co-pending patent application (PCT/GB03/02941 Roddis) which preferably defines a hermetic dual face bearing protector with magnetic attracted seal faces in a cartridge seal format. Like all mechanical seal face designs, the bearing isolator defined in PCT/GB03/02941 may suffer from overheating in marginal lubrication applications as found with oil mist. 
         [0062]      FIG. 2A  is a longitudinal cross-section of the first embodiment of the invention, showing a dual bearing protection mechanical seal  9  with one textured seal face  19  adjacent to the sealed fluid  20 . The sealed fluid  20  is an oil mist in this example. However, it could be any marginal lubrication media including grease, powder or a slurry combination. 
         [0063]    The mechanical seal  9  includes a stationary and axially floating seal face assembly  21  which is magnetically spring biased towards a static rotary seal face  22 . Rotary seal face  22  slides on static seal face  21 , the interface between the seal faces forming a sealing area  23 . This sealing area  23  is the primary seal that prevents fluid medium  20  from escaping from the bearing chamber  25 . 
         [0064]    Fluid medium  20  is also sealed by a rotary elastomer  26  which contacts shaft  27 , thereby forming a first secondary sealing area. A second secondary sealing area is formed between stationary seal face  21  and stationary housing  28  by means of elastomeric member  29 . A third secondary sealing area is formed between the stationary housing  28  and the bearing chamber  25  by means of elastomeric member  30 . 
         [0065]    The primary and secondary sealing area prevent the fluid medium  20  from escaping from the bearing chamber  25 . 
         [0066]    The static seal face  21  is prevented from rotating by one or more drive lugs/pins between seal face holder  30  and housing  28 . In other embodiments, alternative anti-rotation arrangements may be provided. 
         [0067]    The rotary seal face  22  rotates with the shaft  27  due to radial squeeze between the elastomeric member  26  and the shaft  22 . Again, alternative rotational drive devices can be utilised in other embodiments of the invention. 
         [0068]    Stationary seal face  21  is a shrink fitted, two part design. A first, radially inward part is a seal running face  31  which is typically manufactured from a mechanical seal face material such as carbon, tungsten carbide, silicon carbide or a ceramic material. 
         [0069]    The second radially outward part of the seal face  21  is a seal face holder  30 , which is manufactured from a magnetic material. The interface between the seal face holder  30  and the seal running face  31  is preferably sealed by means of a suitable adhesive, or a radial interference fit. 
         [0070]    The two part stationary seal face  21  is longitudinally attracted to the housing  28  by magnets  33 . These magnets  33  are each in the form of a cylindrical bar magnet located in an outwardly extending radial groove  34  in housing  28 . In other embodiments, magnets of different shapes and sizes may be employed. 
         [0071]    The magnets  33  are preferably radially positioned and circumferentially spaced by magnet support ring  40 . Preferably, the radial groove  34 , in housing  28  incorporates an inwardly extending radial lug  41  over a segment of the circumference of the groove  34  as shown in  FIG. 2B . 
         [0072]      FIG. 2B  corresponds to  FIG. 2A  and shows a cross-sectional end view through section A-A. As shown, the magnet support ring  40  carries one or more cylindrical magnets  33 , which circumferentially locate against inwardly extending radial lug  41  in groove  34 . This arrangement provides an anti-rotation feature between the support ring  40  and static bearing housing  25  ( FIG. 2A ), which is considered particularly beneficial should the rotor  22  and/or shaft  27  be radially misaligned and contact the support ring  40 . 
         [0073]      FIG. 2C  is an enlarged partial cross-section, corresponding to  FIG. 2A . Located on the other side of rotary seal face  22  to stationary seal face  21  is a static seal face assembly  45 . The magnets  33  also attract static seal face  45  towards the rotary seal face  22  and the rotary seal face  22  slides on the static seal face  45 . The interface between rotary seal face  22  and stationary seal face  45  provides sliding area  46 , which is not a sealing surface. 
         [0074]    The static sliding seal face  45  has a textured surface  47  which creates at least one communication channel  48  between the innermost radial portion  49  and the outermost radial portion  50  of the seal face. 
         [0075]    As the rotary seal face  22  wipes past the textured stationary seal face  45 , energy is added to the adjacently positioned oil mist particles  20 . This flow turbulence acts to cause the larger oil particles to be deposited around the seal faces. The rate of particle deposition increases with increasing turbulence induced by higher velocities. It has been found that the generated turbulence of a textured seal face  45  is significantly greater than that of an untextured seal face  21 . Said textured seal face  45  turbulence is sufficient to coalesce the oil mist  20  into droplets to provide an efficient wetting of the sliding seal faces  23  and  46 . 
         [0076]    As the larger oil droplets  20  coalesce, the centrifugal forces of the rotating shaft  27  throw them radially outwardly through the stationary communication channel(s)  48  in the textured stationary seal face  45  and into the seal cavity  52 . Once in the seal cavity  52 , the oil droplets  20  gather and are trapped in the radially extending housing groove. This entrapment creates an oil pool  53  which is adjacent to the hermetic sealing interface  21  thus cooling and lubricating it. 
         [0077]    A fourth secondary sealing area is formed by elastomer  54  in radial contact with stationary seal face assembly  45  and housing  28 . 
         [0078]      FIG. 3  corresponds to  FIG. 2A  and shows the end view of the textured seal face  47  on line B-B of the first embodiment. 
         [0079]      FIG. 4  is a longitudinal section of the second embodiment of the invention, showing one textured seal face  70  adjacent to the atmospheric side of the bearing cavity  71 . 
         [0080]      FIG. 5  corresponds to  FIG. 2A  and shows the end view of the textured seal face  47  on line B-B of the third embodiment. The position of the entrapped oil pool  53  is clearly shown. 
         [0081]      FIG. 6  is a partial longitudinal section of the fourth embodiment of the invention, showing the two sets of textured seal faces  80  and  81  of the first and second embodiments, albeit textured seal face  81  is only partially textured across its radial width. Any combination of the first, second and fourth embodiments could be provided with any combination of patterns and by any suitable combination of marking, engraving, texturing, and etching techniques of either seal face in the seal assembly. 
         [0082]    An example is shown in  FIG. 7A  which is an end view of an alternative textured seal face, on line E-E of  FIG. 6 .  FIG. 7B  shows an end view of the partially textured seal face  82 , on line D-D of  FIG. 6 . Preferably, the partial texture  82  extends from the region of the face in contact with the oil pool. In the case of  FIG. 6 , the texture  82  extends from the outermost radial position  83  of the seal face  81  radially inwardly, terminating before communicating with the innermost radial portion  84  of seal face  81 . 
         [0083]      FIG. 8  is a partial longitudinal section through a fifth embodiment of a bearing protector of the invention  90 , showing a combined labyrinth seal  91  and hermetic seal  92 . Labyrinth seal  91  incorporates an agitating feature  93  in the form of one or more inwardly radially extending scallops  94  in the rotor  95  which are adjacently positioned in close radial position to a stator bore  96 . As such, as the rotor  95  rotates with the shaft  97 , the agitator  93  adds energy into the oil mist  98  acting to coalesce it into oil droplets. Said oil droplets  98  collect in a radially extending oil pool cavity  99  thus providing a lubrication and cooling to the hermetic sliding seal face  92 . 
         [0084]      FIG. 9  is a partial longitudinal section through a sixth embodiment of the present invention which is an item of rotating equipment  100  with an oil mist system  101  connected by suitable pipework  102  to an orifice  103  in the bearing protector housing  104 . Orifice  103  communicates with the radial cavity  105  between the textured sliding seal face  106  and hermetic sliding seal face  107 . Oil mist  109  is forced through bearing protector  108  before passing through to the bearings in the rotating equipment  100 . This ensures maximum oil droplet collection, and thus seal face cooling, adjacent to the hermetic sliding seal face  107 . 
         [0085]      FIG. 10  is a longitudinal section through the seventh embodiment of the invention  120 , showing a concentric pair of seal faces  121  and  122 , the radially inwardly positioned one being textured  123  and positioned adjacent to the sealed fluid  124 . As previously described, oil mist  124  coalesces and passes through the textured sliding surface  123  into the seal chamber cavity  125 . As illustrated in  FIG. 11 , the coalesced oil gathers in an oil pool  130  in the radially and/or axially extending cavity positioned adjacent to the hermetic seal face. 
         [0086]    Since the seal faces  121  and  122  are concentrically mounted, the radially outwardly positioned hermetic seal face  121  bathes in the gathered pool of oil droplets  130 . Again, this arrangement provides excellent seal face lubrication to the hermetic sliding seal faced  121 .