Patent Publication Number: US-2005126325-A1

Title: Adjustable leak device for a rotating shaft

Description:
TECHNICAL FIELD OF THE INVENTION  
      This invention relates to a device and method for controlling a leak of fluid from a reservoir over a rotating shaft, which extends into the reservoir.  
     BACKGROUND OF THE INVENTION  
      Various seals and sealing methods exist in the art of preventing the leak of fluid from a reservoir past a rotating shaft, which extends into the reservoir. The main methods used in the art are to use packed seals and mechanical seals. Packed seals rely on a seal formed between the packed material and the shaft and mechanical seals on a seal formed between a sealing surface of abrasion resistant material and a wear face defined by a flange extending from the shaft. The packing material of the packed seal is compressed against the shaft and the resulting friction requires additional energy to rotate the shaft and causes high wear on the shaft. The sealing surface of the mechanical seal is spring loaded or urged against the wear surface also causing high wear of the sealing surfaces. In addition, the mechanical seal and packed seal can also employ pressurised fluid which flows from the outside of the reservoir past the shaft into the reservoir for cooling, lubrication and to prevent leak of fluid from a reservoir past a rotating shaft. This method of lubrication can be mechanically complicated and may contaminate the fluid inside the reservoir. Normally, if the lubrication stops, the seal seizes with catastrophic results. Seizing may also occur during start up if the sealing surface has bonded to the wear surface due to abrasives suspended in the fluid, crystallization, setting or curing of substances in suspension or solution. It will be appreciated that, a corrosive or abrasive fluid inside the reservoir will exaggerate the problems highlighted with existing seals. In a previous application PCT No. PCT/ZA00/00242 the applicants described a mechanical seal in which a sealing surface is urged against a wear surface, which suffers with the problems discussed above.  
     GENERAL DESCRIPTION OF THE INVENTION  
      According to a first aspect of the invention there is provided a device for controlling a leak of fluid through an opening in a wall over a rotating shaft, which rotating shaft extends through the opening, the device including a first adjustable member adjustably mountable to the wall, the member having a generally stationary working surface spaced from a rotating working surface which rotates with the shaft such that an adjustable leak gap is defined between the stationary and the rotating working surfaces to control the leak of fluid through the opening.  
      The adjustable member may be coaxially mountable about the shaft, the member being axially adjustable and having a generally stationary working surface spaced from a corresponding rotating working surface of a flange which extends transversely from the shaft such that an adjustable leak gap is defined between the stationary working surface and the corresponding rotating working surface; and  
      an adjustment means for axially adjusting the member, thereby adjusting the adjustable leak gap.  
      The wall may be any wall, which separates a liquid and a gas medium. Typically, the wall may be a wall of a reservoir or a wall of a housing, such as a pump housing, located inside the reservoir.  
      Typically the shaft and the member may be circular in cross section.  
      The adjustment means may be any suitable means for axial displacement of the member. The adjustment means may include a fixture axially mountable about the member, the member and fixture having complementary threads such that rotational movement of the member causes axial displacement of the member. The adjustment means may then include any mechanical advantage means for rotating the member. In one embodiment, the member may be provided with a co-axial annular gear and the mechanical advantage means being in the form of a worm engaging the annular gear.  
      The adjustment means may include a housing for rotatably housing the worm. The housing may be fastened to the fixture. The worm may further be axially slideable along its axis in the housing and the adjustment means may then include an obstruction means for obstructing or inhibiting slideable movement of the worm such that the annular gear can be operatively rotated by rotating the worm. The obstruction means may include a locking means to obstruct slideable movement of the worm in a first, decreased gap, adjustment, direction and slideable movement of the worm in a second, opposite, increased gap, direction. The obstruction of slideable movement of the worm in the first and second adjustment directions allows the rotation of the member, respectively, to adjustably decrease the leak gap between the working surface of the member and the working surface of the flange and to adjustably increase the gap.  
      Instead, the obstruction means may include an urging means which allow slideable movement of the worm in the second, increased gap, direction, against the urging means. The pitch of the complementary threads of the member and fixture is selected such that, when a rotational force in the second, increased gap, direction is experienced by the member which cause rotational movement of the member against the urging means of the obstruction means, axial movement in the increased gap direction of the member will result.  
      It will be appreciated that, in the event that the working surface of the member and the working surface of the flange adhere together, the rotation of the shaft will apply a rotating force to the member to rotate against the urging means of the obstruction means of the blocking means to cause axial movement of the member to urge the working surfaces apart to prevent the working surfaces from seizing together. Once the working surfaces are urged apart, the urging means of the obstruction means will urge the member back into its adjusted gap position.  
      In use, the device will be mounted about a rotating shaft, the shaft extending into a reservoir and having a flange, which extends transversely therefrom. The device is mounted such that the generally stationary working surface of the adjustable member and the rotating working surface of the flange are in close proximity axially opposite each other. The member is then axially adjusted until the leak gap allows a desired leak rate of fluid from the reservoir.  
      The device may include a second adjustable member similar to the first adjustable member.  
      The second adjustable member may be coaxially mountable about the shaft, the member also being axially adjustable and having a generally stationary working surface oppositely spaced from a corresponding rotating working surface of the flange which extends transversely from the shaft such that a second adjustable leak gap is defined between the working surface of the second member and the corresponding surface of the flange, and an adjustment means for axially adjusting the second member, thereby adjusting the second adjustable leak gap. The second member may be coaxially screw threadedly received inside the first member such that the adjustment means for axially adjusting the second member may be similar to the adjusting means for the first member and such that the working surface of the first member and the working surface of the second member cooperate to define a first outer adjustable leak gap and a second inner adjustable leak gap. It will be appreciated that the second member protects the shaft against undue exposure to leaked fluid.  
      It will be appreciated by those skilled in the art that forces, other than axial forces, also known as forces which cause shaft whip, which act on a rotating shaft may cause transverse movement of the shaft and its flange. In order to accommodate any transference of non axial movement from the rotating surface of the flange and the generally stationary working surfaces of the first and/or second members, and to ensure a constant leak rate, the first and/or second members may be provided with a universal type joint, which extends between the working surface and the annular gear.  
      A universal type joint shall be understood to be a coupling of two parts, the coupling being able to accommodate movement of one or both parts in and out of axial alignment and transmit rotary power from one part to the other.  
      The device may further include a seal between the first member and the wall. The seal may include an outer annular part with an outwardly facing sealing surface, which sealingly bears against an opposed surface of the wall or a fixture thereto, and an inner annular part with an inwardly facing sealing surface, which sealingly bears against an opposed surface of adjustable member. An outer diameter of the outer part may be larger than the outer diameter of the inner part and the inner diameter of the inner part may be smaller than the inner diameter of the outer part. Then, the inner diameter of the outer part is smaller than outer diameter of the inner part and the parts may abut annularly along opposed surfaces on the parts. The seal further includes an urging means for sealingly urging the abutting surfaces together while still allowing movement of the parts along the abutting surfaces relative to each other. The urging means may be one or more screw threaded or spring loaded studs, which bear against the parts. The outwardly facing surface of the outer part may define an annular groove for locating an o-ring and the inwardly facing surface of the inner part may define an annular groove for locating an o-ring. It will be appreciated that such a seal, which is configured to accommodate shaft whip movement, may be used in known mechanical seals, and is therefore a second aspect of the invention.  
      The fixture may have an annular channel defined on the inside thereof and an outlet defined therein for collecting and dispensing any fluid, which leaks from the reservoir through the opening defined in the wall over the rotating shaft. It will be appreciated that, in use, the rate of fluid dispensed from the outlet is proportional to the size of the adjustable leak gap, and the gap can be adjusted accordingly.  
      The fixture may also have an inlet defined therein for flushing the shaft and the, or each member with a cleaning fluid when desired.  
      The end of the second, inner, member opposite its working surface may be sealed against the rotating shaft such that the device forms a chamber for containing collected fluid until it has been drained from the device.  
      The chamber also facilitates flushing of the device during operation.  
      According to a further aspect of the invention, there is provided a method for managing a leak of fluid from a reservoir past a rotating shaft, which extends into the reservoir, the method including the step of mounting a device about a rotating shaft, the device defining an adjustable leak gap, as described above. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The invention is now described by way of example with reference to the accompanying drawings.  
      In the drawings:  
       FIG. 1  shows a sectional side view of a device for controlling a leak of fluid through an opening in a wall over a rotating shaft, in accordance with the invention;  
       FIG. 2  shows a three-dimensional exploded view of the device;  
       FIG. 3  shows a part sectional front three-dimensional view of the device; and  
       FIG. 4  shows a part sectional rear three-dimensional view of the device. 
    
    
      Referring now to the drawings, the device for controlling a leak of fluid through an opening in a wall over a rotating shaft, in accordance with the invention, is generally indicated by reference numeral  10 .  
      The device  10  can, for example, be used to control a leak of water (indicated in  FIG. 1  by the arrows marked  12 ) through an opening  13  in a wall  14  of a water containing reservoir  16  over a rotating pump shaft  18 , which rotating shaft  18  rotates in the direction of the arrow  19  and extends through the opening  13  into the reservoir  16 . For the sake of clarity, the shaft  18  is not shown in FIGS.  2  to  4 .  
      The device  10  includes a first adjustable member  20 , which is coaxially mounted about the shaft  18  to the wall  14 . The member  20  is axially adjustable and has a generally stationary working surface  22  spaced from a corresponding rotating working surface  24  of a flange  26 , which extends transversely from the shaft  18  such that an adjustable leak gap is defined between the stationary working surface  22  and the corresponding rotating working surface  24  to control the leak of water  12  through the opening  13 .  
      The device  10  further includes an adjustment means generally indicated by reference numeral  28  for axially adjusting the member  20 , thereby adjusting the adjustable leak gap and the rate of water leaking through the opening  13 . The adjustment means  28  includes a fixture  30 , sealably mounted to the wall  14 , by means of the flange  32 , and axially about the member  20 . The flange  32  is bolted to the wall  14  by means of bolts  33 . It will be appreciated that, in other embodiments of the invention, the flange  26 , fixture  30  and/or wall  14  can be integrally formed. The member  20  and fixture  30  has complementary threads  34  and  36 , respectively, such that rotational movement of the member  20  causes axial displacement of the member  20 . The adjustment means  28  further includes a mechanical advantage means for rotating the member  20  relative to the fixture  30 . In this embodiment, the member  20  is provided with a co-axial annular gear  38  and the mechanical advantage means is in the form of a worm  40  engaging the annular gear  38 . The adjustment means  28  also includes a housing  42  for rotatably housing the worm  40 . A shaft  43  extends coaxially through and is fast with the worm  40 . The housing  42  is fastened to the flange  32  with two bolts  44 . The worm  40  is axially slideable along its axis in the housing  42  and the adjustment means  28  includes an obstruction means for obstructing or inhibiting slideable movement of the worm  40  such that the annular gear  38  can be operatively rotated by rotating the worm  40 . The obstruction means includes a locking means in the form of a nut  46  screw threadedly received at a first end  48  of the shaft  43  to obstruct slideable movement of the worm  40  in a first, decreased gap, adjustment, direction, indicated by arrow  50 . The shaft  43  passes slideably through a shaft guide  52 . The shaft guide  52  is kept in position in the housing  42  with a locking bolt  54  and nut  56  arrangement. The obstruction means further includes an urging means  58  in the form of a coil spring, which allow slideable movement of the worm in a second, increased gap, direction indicated by the arrow  60 , against the urging means  58 . A nut  59  is lockable to a second end  61  of the shaft  43 . The nut  46  is used to pre tension the spring  58 , then locked to the second end  61  of the shaft  43  with the locking pin  63  allowing the shaft  43  and the worm  40  to be turned with the nut  59  to adjust the adjustable gap.  
      The obstruction of slideable movement of the worm  40  in the first  50  and second  60  adjustment directions allows rotation of the member  20  to, respectively, adjustably decrease the leak gap between the working surface  22  of the member  20  and the rotating working surface  24  of the flange  26  and to adjustably increase the gap.  
      The pitch of the complementary threads of the member  20  and fixture  30  is selected such that, when a rotational force in the second, increased gap, direction  60  is experienced by the member  20 , which cause rotational movement of the member against the urging means  58  of the obstruction means, axial movement in the increased gap direction of the member  20  will result. It will be appreciated that, in the event that the working surface  22  of the member  20  and the working surface  24  of the flange  26  adhere together, for instance at startup of the pump, the rotation of the shaft  18  will apply a rotating force to the member  20  to rotate against the urging means  58  causing axial movement of the member  20  thereby urging the working surfaces  22  and  24  apart, preventing the working surfaces from seizing together. Once the working surfaces  22  and  24  are urged apart, no, or insufficient rotational force is applied to the member  20  and the urging means  58  will urge the member  20  back into its adjusted gap, or working position.  
      The device  10  includes a second adjustable member  62  similar to the first adjustable member  20 . The second adjustable member  62  is also coaxially mounted about the shaft  18 , the member  62  also being axially adjustable and having a generally stationary working surface  64  oppositely spaced from a corresponding rotating working surface  24  of the flange  26 , which extends transversely from the shaft  18  such that a second adjustable leak gap is defined between the working surface  64  of the second member  62  and the corresponding surface  24  of the flange. The device  10  also includes an adjustment means  28  for axially adjusting the second member  62 , similar to the adjusting means for the first member  20 , thereby adjusting the second adjustable leak gap and like reference numerals are used to indicate like parts. The second member  62  is coaxially screw threadedly received inside the first member  20 , in a similar way as the first member  20  is received inside the fixture  30 , such that the adjustment means  28  for axially adjusting the second member  62  may be similar to the adjusting means  28  for the first member  20  and such that the working surface  22  of the first member  20  and the working surface  64  of the second member  62  cooperate to define a first outer adjustable leak gap and a second inner adjustable leak gap.  
      Forces, other than axial forces, also known as forces, which cause shaft whip, which act on a rotating shaft may cause transverse movement and/or vibrations of the shaft and its flange. In order to accommodate any transference of non axial movement from the rotating surface  24  of the flange  26  and the generally stationary working surfaces  22  and  64  of the first and or second members  20  and  62 , and to ensure a constant leak rate, the first and/or second members  20  and  62  are provided with a universal type joint  68  and  70 , respectively, which extends between each working surface  22  and  64  and its respective annular gear  38  and  66 . Each joint  68  and  70  includes two oppositely facing swivel parts,  72  and  74  for the first, outer, member and  76  and  78  for the second, inner, member, swivelably mounted at right angles relative to each other to and over respective mounting rings  80  and  82 . One swivel part  72  and  76  of each joint  68  and  70 , respectively, is connected to a respective ring  84  and  86 , each having its respective working surface  22  and  64 . Two o-rings  88  seal the outer surface of the ring  86  against the respective inner surfaces of the parts  76  and  78  to minimise the shaft  18  to exposure to leaked water.  
      The device  10  further includes a seal generally indicated by numeral  90  between the first member  20  and the fixture  30 , which in turn is sealingly mounted to the wall  14 . The seal  90  includes an outer annular part  92  with an outwardly facing sealing surface  94 , which sealingly bears against an opposed surface of the fixture  30 , and an inner annular part  96  with an inwardly facing sealing surface  98 , which sealingly bears against an opposed surface of the swivel part  72  of the adjustable member  20 . The outwardly facing surface  94  of the outer part  92  defines an annular groove for locating an o-ring  100  and the inwardly facing surface of the inner part  96  defines an annular groove for locating an o-ring  102 . An outer diameter of the outer part  92  is larger than the outer diameter of the inner part  96  and the inner diameter of the inner part  96  is smaller than the inner diameter of the outer part  92 . Then, the inner diameter of the outer part  92  is smaller than outer diameter of the inner part  96  and the parts  92  and  96  abut annularly along opposed surfaces on the parts  92  and  96 . The seal  90  further includes an urging means in the form of screw threaded studs  104  received in threaded apertures defined in the fixture  30  for sealingly urging the abutting surfaces together while still allowing some movement of the parts  92  and  94  along the abutting surfaces relative to each other. A ring  105 , of which an outer portion fits inside a groove defined in the inner surface of the fixture  30  adjacent the outer part keeps the parts  92  and  96  in position. It will be appreciated that the seal  90  is configured to accommodate shaft whip movement and/or vibrations.  
      The fixture  30  has an annular channel  106  and an outlet  108  defined therein for collecting and dispensing any water, which leaks from the reservoir  16  through the opening  13  defined in the wall  14  over the rotating shaft indicated by the arrows  12 . It will be appreciated that, in use, the rate of water dispensed from the outlet  108  is proportional to the size of the adjustable leak gap, and the gap can be adjusted accordingly.  
      The fixture also has an inlet  110  defined therein for flushing the channel  106 , each member  20  and  62  and other parts with a cleaning fluid when desired.