Abstract:
The invention describes a leak proof shaft seal for valves and other pressurized vessels, wherein the shaft seal can deform elastically by either stretching or twisting without loosing its ability to seal all, or a portion, of said shaft from harmful fluids. Furthermore, the elastic shaft seal is immune to static pressures, since it closely surrounds a shaft and thus is protected from collapse.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to a device to seal shafts or stems penetrating into pressurized vessels in order to activate valves or other mechanisms and where it is desirable to seal said shafts or stems, and the opening through which said shafts or stems pass, from hazardous fluids passing or being contained within said valves or vessels. 
     Seals for stems heretofore employed were metal or plastic bellows, or flexible diaphragms. While bellows, as shown in my U.S. Pat. No. 5,058,861, are prone to fatigue problems, have limited excursions, and are limited to low pressures, diaphragms, as shown in my U.S. Pat. No. 4,609,178 can only be used for reciprocating stem motion, have limited excursion capabilities, are very space demanding, and are limited to relatively low pressures. They also require high actuating forces for motivation, caused by the fluid pressure acting on such a relatively large diaphragm area. This is a major cost item. 
     The present invention overcomes such difficulties in that a flexible tube (typically made from a rubber compound) is employed, surrounding and sealing said stems or shafts. Such a tube can easily be stretched over 100% of its original length without loosing its elasticity (depending on the material used) and is practically insensitive to fluid pressure, since the tube can not collapse, being completely supported, at the inside, by the passing stem or shaft. There is only an insignificant increase in actuating force above that caused by the fluid pressure acting on the cross-sectional area of the stem itself. 
     The tube, besides being able to be stretched, can likewise be twisted around a shaft by more than 180 degrees thereby permitting rotary actuations. 
     Furthermore, my sealing device is very compact since it requires an opening within a valve or vessel that is only slightly larger than the shaft or stem itself. This is a major cost improvement over current, state of the art, devices. 
     Finally, the manner of sealing the upper and the lower terminal ends of my tubular seal avoids the entrapments of poisonous matter or of micro-organisms. 
     SUMMARY OF THE INVENTION 
     The invention relates to sealing devices for shafts in rotary devices manipulators, or reciprocating valve stems that require seals in order to prevent fluid from escaping from a fluid filled vessel into the open. The invention consists of a tubular member passing over that portion of a stem or shaft normally exposed to fluid, wherein one end of said tubular member is sealed and fixed onto an opening within a pressurized vessel or container, and wherein the other end is sealed and fixed against the movable shaft or stem, thus allowing for the longitudinal or rotary excursion of the stem within a fluid filled device. My invention furthermore has a wedging mechanism to achieve both the sealing as well as the retention of the aforementioned ends of the tubular member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate preferred modes of construction. In the drawings: 
         FIG. 1  is a sectional view of a globe valve having a reciprocating stem seal. 
         FIG. 2  is a sectional, partial view of the top portion of the device shown in  FIG. 1 , with the upper sealing mechanism shown prior to being compressed. 
         FIG. 3  is sectional, partial view of the lower portion of the device of  FIG. 1 , with the sealing mechanisms shown prior to being compressed. 
         FIG. 4  is a sectional view of a butterfly valve, showing the vane in the partially open position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates my invention as part of a conventional globe valve, comprising a housing  1  having flanged ends  2  capable of connecting an inlet port  3  and an outlet port  4  to a pipeline. An orifice  5  straddling the inlet and outlet ports co-operates with a valve plug herein after called “shaft extension”  6 , here shown in the open position. Housing  1  furthermore has a tubular extension  7  incorporating therein a slid able valve shaft  8 . 
     Said tubular extension  7  has an upper threaded, terminating portion  9 , engaging therewith a threaded cupped nut  10  capable of compressing a slid able bonnet  11  made from metal or a hard plastic and having a lower convex conical section  12  and a tubular appendix  12   a . Bonnet  11  and cupped nut  10  have a central, circular bore  13  to guide shaft  8 . 
     Shaft  8  is enveloped, along a portion which extends into the portion of housing  1  which is subjected to fluid pressure by a tubular element defining a shaft seal  14 . Said tubular element has an upper sealing portion  15  resting on a stepped shoulder  16  being part of tubular extension  7 . Sealing portion  15  furthermore has a concave, conical section  17  able to receive the lower, conical section  12  of bonnet  11 . 
     A tightening of nut  10  will drive bonnet  11  down and force convex section  12  to engage and compress the upper sealing portion  13  against the stepped shoulder  16  and radially outwards against wall  18  thereby providing a leak proof seal against a pressurized fluid. Tubular appendix  12   a  is interspaced between the compressed upper sealing portion  15  and the movable shaft  8  in order to prevent friction caused by the swelling of upper sealing portion  15 , that could impede the smooth motion of shaft  8 . 
     The lower terminating end of shaft  8  has a threaded, reduced diameter portion  19  engaging a tubular, conical ring  20  and furthermore engaging a conical portion  21  of the tubular element, made of a deformable material such as rubber. The lower end of the reduced diameter portion  19  threadingly engages a shaft extension  22  (a valve plug, in the example shown) having an upper, enlarged recess  23 , encompassing a radial groove  24  engaging therein the lower, terminating part of tubular element  14  together with conical portion  21 . 
     Any tightening of the reduced diameter portion  19  into the shaft extension  6  forces conical ring  20  to engage conical portion  21  and thereby radially deform the latter, thereby forcing the lower portion of the tubular member  14  to expand into groove  24  thus providing an effective fluid seal and means to retain the shaft seal from being pulled out of groove  24 . 
     Shaft extension  6  will approach and close orifice  5  whenever shaft  8  is being extended downwards. Tubular member  14  has to stretch (being made of an elastomeric material) following any excursion of shaft  8  since being restrained both on top, by stepped shoulder  16 , and on the bottom by groove  24 . This prevents fluid from contacting the surfaces of shaft  8  or, more importantly, from escaping between shaft  8  and bore  13  to the exterior of housing  1 . 
     A second, preferred application of my invention is illustrated in  FIG. 4  showing a butterfly valve constituting a pressure vessel, and shown in a partially open position. Here a housing  25  has a circular bore  26  enclosing therein a vane  27  having a cross-sectional bore  28  retaining therein a shaft  29  extending to the exterior of housing  25 . 
     Bore  28  is subjected to fluid pressure emanating from housing bore  26 . A bonnet  30  extending through an opening  31  in housing  25  is adjustably connected to housing  25  by a pair of screws  32 . Bonnet  30 , made from metal or a hard plastic, has a lower convex conical section  33 . Bonnet  30 , furthermore has a central circular bore  34  to guide shaft  29 . 
     Shaft  29  is enveloped, along a portion which extends into the interior portion of vane  27  which is subjected to fluid pressure, by a tubular element  35 . Said tubular element has an upper sealing portion  36  resting on a guide bushing  37  supported in turn by a stepped shoulder  38  at the upper end of bore  28 . Sealing portion  36  furthermore has a concave, conical section  39  able to receive the lower, convex section  33  of bonnet  30 . 
     A tightening of screws  32  will drive bonnet  30  down and force convex section  33  to engage and compress the upper seating portion  36  against the guide bushing  37  and radially outwards against the wall of bore  31  thereby providing a leak proof seal against a pressurized fluid. 
     The lower terminating end of shall  29  has a threaded, enlarged diameter extension  40  engaging a tubular threaded member  41  having a concave reduced diameter portion  42  and furthermore engaging a conical ring  43  made of a deformable material such as rubber. The portion of the shaft  29  next to the enlarged diameter extension  40  has an external circumferential groove  45 . 
     Any tightening of the enlarged diameter extension  40  forces the concave diameter portion  42  to engage conical ring  43  and thereby radially deform the latter, thereby forcing the lower portion of the tubular member  35  to contract into groove  45 , thereby providing an effective fluid seal and means to retain the shall seal from being pulled or twisted out of groove  45 . 
     Any rotary motion of shaft  29  in turn motivates vane  27  via a pin  46  and will result in a twisting of said tubular member  35  without subjecting the exterior of housing  25  to fluid leakage. While shaft  29  is turning, upper seal  36  and bushing  37  remain stationary, while lower seal  43 , extension  40  together with vane  27  rotate. 
     While the invention has been shown in preferred embodiments, numerous modifications can be made without departing from the spirit and intent of my invention. For example, rather than being compressed by a nut, my bonnet could be threaded within the tubular extension of the housing, and then screwed down to effect the seal. In addition, it might be desirable to have the shaft undergo a combined longitudinal and rotary motion. 
     It may also be desirable to have the shaft&#39;s outer surface coated with a suitable lubricant in order to reduce friction between the shaft and the interior of the tubular member. 
     While it is preferred to have the upper and the lower sealing portions being integral parts of the tubular member, it is recognized, that these parts could be separate and being later joined either by friction or by being joined upon application of a suitable glue.