Abstract:
Rotary barrier face seal of the non-contact type seal with helical grooves for a housing and a shaft, comprising means for introduction of an external barrier fluid towards the sealing interface. Said barrier fluid prevents sealed process fluid from entering past the sealing interface, thus providing sealing means for hazardous or repugnant fluids.

Description:
TECHNICAL FIELD 
     The invention relates to sealing devices for rotatable shafts, where either sealed or barrier fluid is employed to generate hydrostatic and hydrodynamic forces or aerostatic and aerodynamic forces between stationary and rotary seal faces to establish separation for their non-contact operation. 
     BACKGROUND OF THE INVENTION 
     Rotary fluid film face seals, also known as non-contact seals are applied to high speed and high pressure rotary shaft sealing operations, where otherwise face contact would cause excessive heat generation resulting in wear and tear of the seal faces. In a non-contact seal face operation, seal faces will separate when rotational velocity reaches lift-off speed and thus undesirable face contact is avoided. 
     A most successful method of generating non-contact separation between two sealing faces is by applying a shallow helical groove pattern on either one of the surfaces of the sealing faces, while the opposite sealing face remains flat and smooth. The area where the two sealing faces define a sealing clearance is labeled the sealing interface. The referred helical groove pattern applied to one of the sealing faces extends inward from the higher pressure circumference of the outer diameter to the inner end of the helical groove specified as the groove diameter. 
     The helical groove pattern forces fluid during shaft rotation from the higher pressure end of the sealing interface toward said groove diameter and thus drives the sealed fluid into remaining non-grooved portion of the sealing interface, thus keeping the sealing faces separated. While a certain amount of fluid will pass through the sealing interface from the side of higher pressure to the side of lower pressure, such fluid amount is considered the seal leakage, an undesirable result of the need to maintain seal face separation. The cooperation between the helical grooved area and the non-grooved area on one of the sealing faces is a most effective approach to maintain a stable gap designated the sealing clearance. 
     The helical groove pumping action is an effective mechanism to move fluids in between the sealing interface, regardless of whether there are pressure differences or even against pressure differentials. Moreover, even in reversed pressure differential situations, the helical groove seal still operates with adequate separation between the sealing faces, but invariably accompanied by a certain amount of leakage. Such seals are frequently used to divide two different fluids near atmospheric pressure from each other or in contingencies where intermixing of fluids must be prevented if one of them is flammable and the other one is air. 
     STATEMENT OF THE PRIOR ART 
     With the presence of elevated rotational velocities and pressures it becomes increasingly difficult to establish a true barrier to prevent intermixing of fluids in non-contact operation. Prior art solutions include the introduction of a third, less chemically active fluid defined as an inert fluid using Nitrogen, Carbon Dioxide or Helium to establish a barrier in a process called buffering. Said buffering can take two forms, either outside or within the sealing interface. Buffering outside the sealing interface requires incomparably larger amounts of costly inert gas due to large radial clearances requiring high flow rats of fresh, uncontaminated buffer fluid, whereas buffering inside the sealing interface, where both sealing clearances and fluid volume subjected to intermixing require much smaller amounts of buffer fluid. U.S. Pat. No. 4,523,764 provides for such purpose a buffer flow inlet as well as buffer flow outlet towards and away from the sealing interface, which as opposed to the present invention requires at least two fluid flow connections to the sealing face to establish a sealing clearance, then to recover part of the buffer fluid and more to provide for a true barrier function. 
     U.S. Pat. Nos. 4,212,475, 3,704,019 and 3,499,653 on the other hand, employ spiral grooves to establish a stable sealing clearance, but does not provide a solution to sealing applications, where true fluid separation or barrier is mandated. 
     STATEMENT OF THE INVENTION 
     According to the invention, buffer fluid is injected directly into and adjacent the upstream end of the sealing interface, with buffer fluid pressure slightly above that coming from the process end of the barrier unit, whereby some amount of buffer fluid is leaking towards the direction of the process, such being diametrical to that of normal interface flow and therefore terminating process fluid flow towards the sealing interface. Said amount of leakage is notably modest since it occurs through an extremely small sealing clearance of less than about 35 microns, preferably less than about 12 microns as compared to 120 microns, when buffering takes place outside the sealing interface. Resulting buffer fluid intermixing, consumption and cost being orders of magnitude smaller, when buffered inside the sealing interface, where above extremely small sealing clearances are a true result of optimum utilization of partial helical groove pattern. 
     Said minimal buffer fluid consumption makes it possible to minimize flow passages, which in turn facilitates the provision of more interface area for partial helical grooves, thus enhances a narrower and more stable clearance. Minimal buffer fluid consumption also makes it possible to avoid having to recover buffer fluid and having to provide flow passages for it which would once further reduce the sealing interface area needed for the advantageous benefits of the partial helical grooves. 
     These and many other features and attendant advantages of the invention will become apparent as the invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an axial quarter sectional view, showing an identical tandem arrangement of a Rotary Barrier Face Seal; 
     FIG. 2 is a view in elevation, partially in section of the sealing face taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a view in elevation, partially in section of the sealing face taken along line  3 — 3  of FIG. 1; 
     FIG. 4 is an enlarged sectional view taken along line  4 — 4  of FIG. 3; 
     FIG. 5 is an axial quarter sectional view of an alternate embodiment of the Rotary Barrier Face Seal; 
     FIG. 6 is a view in elevation, partially in section of the sealing face taken along line  6 — 6  of FIG. 5; 
     FIG. 7 is a view in elevation, partially in section of an alternate embodiment of the sealing face; and 
     FIG. 8 is a view in elevation, partially in section of a further embodiment of the sealing face. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 displays the preferred embodiment of the invention and its environment. This environment comprises a housing  10  and a rotatable shaft  12 , extending through said housing. The invention is applied to seal and separate fluid within the annular space  14  from the fluid environment at  16 . 
     Basic components of the rotary barrier seal face of the invention comprise an annular stationary ring  20 , having a radial extending face  22  in sealing relation with a radial extending face  26  of an annular rotary ring  24 . The stationary ring  20  is held in place by an annular retainer  40 , and its outer diameter engages a lip of the low friction static seal  60 . Cover  18  locks the retainer  40  and the static seal  60  against the shoulder  48  of the housing  10  to prevent axial movement. 
     An O-ring seal  56  extends around the outer circumference of the retainer  40  to preclude leakage of buffer fluid at ports  58  and  64  into fluid environment  16  between retainer  40  and housing  10 . Amid retainer  40  and stationary ring  20  is a plurality of springs  46 , spaced equidistantly around the circumference of retainer  40 . Springs  46  act against an annular disc  44 , urging the stationary ring  20  into engagement with the rotary ring  24 . An O-ring  42  seals the space between the stationary ring  20  and retainer  40 . The rotary ring  24  is retained in the axial position by the drive sleeve  36  and the clamp sleeve  34 . Drive sleeve  36  and clamp sleeve  34  are concentric with the shaft  12  and both are locked on to the shaft  12  between shaft shoulder  62  and locknut  38  threaded onto shaft  12 . The O-ring seals  50  and  52  preclude leakage between the rotary ring  24 , the drive sleeve  36  and the shaft  12 . 
     In operation, radial extending face  22  of the stationary ring  20  and radial extending face  26  of rotary ring  24  are in sealing relationship, maintaining a very narrow sealing clearance, generated by a helical groove pattern  28  on the sealing face  26  of the rotary ring  24 . Opposite arrangements with said helical groove pattern on the sealing face  22  of the stationary ring  20  are also effective and will be shown below. 
     Said narrow clearance prevents generation of friction heat and wear, yet limiting consumption and outflow of the buffer fluid supplied through opening  30  into crescent-shaped pockets  32  which have a pressure-equalizing function, whereas the same function can also be achieved by means of an annular recess, which will be shown below. 
     FIG. 2 shows a view in elevation of the sealing face  26  of the rotary ring  24  with a pattern of helical grooves  28  according to FIG. 1, taken along line  2 — 2 . Shown helical grooves  28  are directed counter-clockwise and inward for a particular direction of shaft rotation and will be directed clockwise and inward for the opposite direction of shaft rotation. Non-grooved area  54  at the outside diameter of the sealing face  26  fosters restriction of outflow of buffer gas into process fluid at annular space  14  of FIG. 1 as will be shown below. 
     FIG. 3 is a view in elevation of the seal face  22  of the stationary ring  20  according to FIG. 1 taken along line  3 — 3 . Exposed are openings  30  for the supply of the buffer fluid. Pressure of said buffer fluid is circumferential equalized by concentric crescent-shaped pockets  32 , whilst outward outflow of said buffer fluid is restricted between narrow dam  66  and the non-grooved area  54  of the sealing face  26  as shown in FIG.  2 . Although FIG. 3 shows said crescent-shaped pockets within stationary ring  20 , the same pressure equalizing arrangements will also be effective with said pockets within said rotary ring. 
     FIG. 4 shows an enlarged view in section taken along line  4 — 4  of FIG. 3, through both stationary ring  20  and rotary ring  24 . Arrows within clearance between rotary ring  24  and stationary ring  20  show the direction of buffer fluid outflow from pockets  32  and opening  30 , exposing the key mechanism for maintaining separation of process fluids between space  14  and at environment  16  according to FIG.  1  and according to FIG. 5 shown below. 
     FIG. 5 shows another embodiment of the invention, where low friction static seal  68  engages with the bore of the retainer  40  and rests within disc  44 . An additional O-ring  76  between disc  44  and stationary ring  20  prevents intermixing of buffer fluid and process fluid at space  14 . Static O-ring seals  70  and  72  as well as  74  help channel said buffer fluid via ports  58  and  64  toward openings  30  and a circumferential groove  33 . 
     FIG. 6 shows a view in elevation of the sealing face according to FIG. 5 taken along line  6 — 6 , where the partial helical groove pattern is formed in the sealing face  22  of the stationary ring  20 . Circumferential groove  33  is located near the stationary ring  20  outer diameter, from which it is separated by a narrow dam  66 . Said circumferential groove  33  serves to equalize buffer fluid pressure circumferentially, while it can be formed in either one of the two sealing faces to obtain the above purpose. Inner circumference of the groove  33  defines outer extent of the pattern of helical grooves  28 . 
     FIG. 7 shows another embodiment of the elevation view of the rotary ring  24  according to FIG. 1 taken along line  2 — 2 . This arrangement does not embrace a non-grooved dam area at the outer diameter of the face  26  and my be applied in situations where helical groove pattern is exceedingly shallow. 
     FIG. 8 shows another embodiment of the elevation view of the stationary ring  20  according to FIG. 1 taken along line  3 — 3 . A plurality of openings  30  supply buffer fluid into the sealing face  22  of said stationary ring  20 . 
     It is to be realized that only preferred embodiments of the invention have been described and that numerous substitutions, modifications and alterations are permissible without departing from the spirit and scope of the invention as defined in the following claims.