Patent Abstract:
A primary object of the present invention is to achieve a high sealing performance, to collect hazardous gas contained in a sealed process fluid, and to realize an easy disposition of a mechanical seal device. A typical configuration is that the end face of a shaft sleeve engages a rotary shaft by a step shoulder of the shaft which is disposed in the sealed fluid side relative to the stationary seal ring, and that the inner diameter of the end face is set larger than the inner diameter of the sealed fluid pressure surface on the back face of the stationary seal ring. This construction makes it easy to dispose a mechanical seal device and with this mechanical seal device, the sealed process fluid is securely sealed.

Full Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to a mechanical seal device with an improved sealing ability and an easy installation of a shaft sleeve. More particularly, the invention relates to a mechanical seal device which retains a relative pressure difference in fluid pressure of a sealed fluid chamber, an intermediate chamber and a buffer fluid chamber to enhance its sealing ability. 
   2. Description of the Related Art 
   There has been a mechanical seal device as a relative art of the present invention, as shown in  FIG. 3 .  FIG. 3  shows a half sectional view of the shaft seal device. 
   In  FIG. 3 , a shaft seal device  100  is disposed between the inner diameter surface of a housing  160  and the outer diameter surface of a rotary shaft  150 . This shaft seal device is a tandemly configured mechanical seal device. This tandem type mechanical seal device comprises a contacting type mechanical seal device  101  in the region of sealed process fluid and a non-contact type mechanical seal device disposed in the atmospheric region. 
   In the contacting type mechanical face seal  101 , a rotary seal ring  102  and a stationary seal ring  103  are disposed adjacent and opposite to each other. The rotary seal ring  102  and the stationary seal ring  103  make a sealing contact at respective sealing faces  104  and  105  wherein the rotary seal ring  102  is fixedly connected to one of split parts comprising a second shaft sleeve  141  and the mating stationary seal ring  103  is fixedly connected to a second seal cover  131 . The sealing faces  104 ,  105  are elastically pressed against each other by springs  107  which are disposed on the back face  106  of the stationary seal ring  103 . In addition, the pressure exerted on the back face  106  by the sealed process fluid pushes the sealing face  104  against the sealing face  105 . An O-ring  108  is disposed on the inside diameter surface of the stationary seal ring  103  which determines the pressure area of the back face  106 . 
   In the non-contact type mechanical seal device  110 , a second rotary seal ring  111  and a second stationary seal ring  115  make a sealing contact at a second sealing face with spiral grooves  113  and a second sealing face  112 , respectively. Contact between the second sealing face with spiral grooves  113  and the second sealing face  112  is further reinforced by a spring  116  and the pressure of purge gas exerted on a back face  117  of the stationary seal ring  115 . The pressure area of the back face  117  is determined by an O-ring  119  which is disposed in the inner annular groove of the back face  117 . The second stationary seal ring  115  is axially movable relative to a first seal cover  132  so that the second sealing face  112  is sufficiently biased by the spring  116  against the second sealing face with spiral grooves  113 . 
   The rotary seal ring  111  fits over a first shaft sleeve  140  and is retained between a third shaft sleeve  142  and the mating part of the split parts of the second sleeve  141 . 
   The flange of the first sleeve  140  engages a step of a rotary shaft  150 . The first sleeve  140  fixates the second sleeve  141  and the second rotary seal ring by means of the third sleeve  142 . Furthermore, a lock nut  143  engages a screw thread  144  prepared on the rotary shaft  150  so as to prevent the first sleeve  140  and the third sleeve  142  from moving in an axial direction. These three sleeves,  140 ,  141 ,  142 , are separated parts and five O-rings  146  are installed for the sake of sealing 
   A seal cover fixedly connected to the housing  160  is comprised of a first seal cover  131  and a second seal cover  132 . The seal covers  131  and  132  are fixedly held between a step of the housing  160  and a presser cover  133 . The seal covers  131  and  132  have a passage  121  to feed a purge gas into an intermediate chamber C′. Pressure of the purge gas is set lower than the pressure of the sealed process fluid. 
   The shaft seal device  100  constructed accordingly has to be able to retain the primary seal ring  102  and the secondary seal ring  111  so that they are free to rotate. Therefore, it is not only that the first, the second, and the third sleeves  140 ,  141 ,  142  become large in size, but that they have to be separable. Being separable parts then necessitates as many as five O-rings  146 . This in turn yields a mass increase of the first, the second and the third sleeves, which requires a large diameter of the rotary shaft  150  to assure a high speed rotating motion. In addition, the tandem configuration of the mechanical seal device leads to a large axial length. 
   Since the pressure of the intermediate chamber C′ is lower than the pressure of the sealed process fluid, there may be a leakage of the sealed process fluid into the intermediate chamber. Also the mechanical seal device  110  residing in the atmospheric region is a non-contact type, therefore the purge gas may leak to the atmospheric region. Accordingly, there remain problems in the seal performance of the shaft seal device  100 . 
   The present invention is introduced to resolve the above mentioned problems. A primary technical goal which this invention tries to achieve is to collect the sealed process fluid with no leakage to the atmospheric region by enhancing the seal performance of the seal parts against the atmosphere region. 
   Another goal is to collect all the leaking fluid into the intermediate chamber without further leaking to the atmospheric region by means of the pressure of the intermediate chamber not only being set lower than the pressure of the sealed fluid but also being set lower than the pressure of the buffer fluid chamber. 
   Yet another goal is to fixate sleeves without use of fitting devices, to reduce the weight of the sleeves and their fitting devices, to achieve a high-speed rotating motion of the rotary shaft, and to reduce a production cost by decreasing the number of parts as the result of a weight reduction of the sleeves. 
   SUMMARY OF THE INVENTION 
   A primary object of the present invention is to resolve the above mentioned technical problems, and a solution to such problems is embodied as follows. 
   A preferred embodiment of a shaft seal device constructed in accordance with the principles of the present invention is a mechanical seal device with a sealed process fluid being sealed between the inner surface of a housing and a rotary shaft retained within the housing, the shaft seal device comprising a stationary seal ring and a rotary seal ring, the stationary seal ring sealingly fixed to the housing being axially biased by a spring and having a primary sealing face on one end whose other back face being pressurized by the sealed process fluid, the rotary seal ring fixedly connected to a sleeve being disposed in the sealed process fluid side relative to the stationary seal ring and having a secondary sealing face adjacent the primary sealing face, an end face of the sleeve engaging a shoulder of the rotary shaft which is disposed in the sealed process fluid side relative to the stationary seal ring, the end face having an inner surface diameter which is larger than the inner diameter of the back face of the stationary seal ring pressurized by the sealed process fluid. 
   In a shaft seal device as an embodiment of the present invention, the sealed process fluid exerts a larger force to the back face of the stationary seal ring than to the end face of the sleeve, therefore enabling the sleeve to engage the shoulder of the rotary shaft. Accordingly, the sleeve does not require a fitting device for fixing and thinning the wall thickness of the sleeve results in a reduction in weight. As a consequence, omitting fitting devices and thinning the sleeve yields a reduction in the total size of the mechanical seal device. The reduction in weight then makes it easy for the mechanical seal device to undergo a high speed rotating motion. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a half cut-away sectional view showing one preferred embodiment of a mechanical seal device of the present invention. 
       FIG. 2  is an enlarged sectional view of a portion of the mechanical seal device shown in  FIG. 1 . 
       FIG. 3  is a half cut-away sectional view of a mechanical seal device according to the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Described below is details of the figures of a preferred embodiment of a shaft seal device constructed in accordance with the principles of the present invention. All the figures explained below are constructed according to actual design drawings with accurate dimensional relations. 
     FIG. 1  shows a half cross sectional view of a mechanical seal device in accordance with the present invention.  FIG. 2  is a cross sectional view enlarging a sealed fluid region HP of  FIG. 1 . 
   In  FIG. 1  and  FIG. 2 , a mechanical seal device  1  is disposed between the inner surface of a housing  60  and a rotary shaft  50 . The mechanical seal device  1  mainly comprises a stationary seal ring  3  and a rotary seal ring  10 . 
   The stationary seal ring  3  is retained in an annular groove of a seal cover  30  so as to move freely in an axial direction. In the back face  5  of the stationary seal ring  3 , multiple biasing springs are disposed concentrically and equally spaced apart. A primary O-ring  19  made of rubber is disposed between a circumferential surface of the annular groove and an inner diameter surface of the stationary seal ring  3 . By use of the primary O-ring  19 , the sealed process fluid exerts pressure upon a surface radially extending from the inner diameter of the primary O-ring  19  to the outer diameter surface of the stationary seal ring  3 . The pressure area of the surface becomes equal to the area of a back face upon which the sealed process fluid and the biasing spring  4  exert pressure to thrust forward the stationary seal ring  3 . 
   This stationary seal ring  3  is retained such that a cavity  7  and a primary lock pin  15  inserted into the cavity  7  prevents the ring  3  from rotating, and a sealing face  6  resides on a front surface of the stationary seal ring  3  opposite to the back face  5 . 
   In a rotary seal ring  10  disposed against the stationary seal ring  3 , a sealing face  16  is disposed in such a way that the face  16  forms a sealing contact with the sealing face  6 . The rotary seal ring  10  fitted over the rotary shaft  50  is constructed so as to rotate with the shaft  50  by means of an anti-rotation mechanism in which a protruding drive pin  44  is inserted to a lock bore  12 . A secondary O-ring  47  is disposed between the two fit surfaces of the rotary seal ring  10  and the shaft sleeve  40  so as to achieve a sealing contact between the rotary seal ring  10  and the shaft sleeve  40 . 
   The rotary shaft  50  has a shoulder  52  in the sealed fluid region HP. A secondary lock pin  53  is fixedly connected adjacent the shoulder  52  of the rotary shaft  50 . A diameter surface in which the secondary lock pin  53  is fixed forms a fit surface  51 . The rotary shaft  50  is made smaller in diameter in an atmospheric region LP. 
   The shaft sleeve  40  fitted over the rotary shaft  50  is made large in wall thickness in the sealed fluid region HP, and an end face  42  of the sleeve  40  is formed at the interface where the sleeve engages the shoulder  52  of the rotary shaft  50 . 
   Inside the neighborhood of the end face  42  of the shaft sleeve  40  is formed a primary inner diameter surface  41  fitted over the fit surface  51 . A third O-ring  56  is disposed between the fit surface  51  and the primary inner diameter surface  41 . The third O-ring  56  provides a sealing between the fit surface  51  and the primary inner diameter surface  41 . Furthermore, a tapered shoulder is disposed inside the sleeve  40  between the primary inside diameter surface  41  and a secondary inner diameter surface  41 A, and an auxiliary through passage  45  is formed in the tapered shoulder. A fourth O-ring  57  is disposed in the atmospheric side LP of the tapered shoulder between the shaft sleeve  40  and the rotary shaft  50 . In case of a leakage of the sealed process fluid from the third O-ring  56 , the fourth O-ring  57  hinders further leakage such that the leaked fluid is guided to flow into an intermediate chamber B via the auxiliary through passage  45 . 
   A symmetrically opposite pair of a first seal part  20 A and a second seal part  20 B are disposed inside a buffer fluid chamber C which resides inside the seal cover  30  fixed to the housing  60  as well as toward the atmospheric side of the cover  30 . The first seal part  20 A and the second seal part  20 B are segment seals. In addition, multiple biasing springs are disposed concentrically and equally spaced apart between the first seal part  20 A and the second seal  20 B. The springs  24  impinge upon the first seal  20 A and the second seal part  20 B in axially opposite directions so that a first sealing face  21 A of the first seal part  20 A makes a sealing contact with the mating face of the seal cover  30  while a second sealing face  21 B of the second seal part  20 B makes a sealing contact with the mating seal cover face of a segmented seal cover  39 . 
   Garter springs  24  and  25  engage outside diameter surfaces of the first seal part  20 A and the second seal part  20 B, respectively, and the first seal part  20 A and the second seal part  20 B being comprised of concentrically and equally spaced segments are fastened radially inward against the rotary shaft  50 . The first seal part  20 A and the second seal part  20 B form a good seal with the rotary shaft  50  by an inner diameter sealing face  22 A of the first seal part  20 A and an inner diameter sealing face  22 B of the second seal part  20 B, respectively. The first seal  20 A and the second seal  20 B are retained by respective lock pins  26  fixedly connected to the seal cover  30 . The buffer fluid chamber C is enclosed by the first seal part  20 A and the second seal part  20 B accordingly. 
   Segmented seal cover  39  fitted over the seal cover  30  in the atmospheric region LP is retained within the seal cover  30  by means of a snap ring  27 . The snap ring  27  engages an annular groove disposed in the seal cover  30 . A locating snap ring  49  disposed in the atmospheric side LP of the shaft sleeve  40  engages an annular groove  48  of the shaft sleeve  40  in a disconnectable manner. The snap ring  49  is disposed in such a way that not only the mechanical shaft seal  2  but also the first seal part  20 A and the second seal part  20 B are retained together between the seal cover  30  and the shaft sleeve  40 . Therefore, the snap ring  49  can be removed from the sleeve  40  after the completion of assembly. 
   Once the mechanical seal device  1  is installed in a hydraulic machine, even after the snap ring  49  is removed from the shaft sleeve  40 , the pressure of the sealed process fluid firmly thrusts the sleeve  40  against the shoulder  52  of the rotary shaft  50  because the pressure area of the back face  5  of the stationary seal ring  3  is larger than the pressure area of the end face  42  of the shaft sleeve  40 . The press contact state is explained by the fact that an inner diameter D of the primary inside diameter surface  41  of the shaft sleeve  40  is set larger than an inner diameter d of the back face  5  of the stationary seal ring  3 , and that a pressure exerted to the portion of the back face  5  in accordance with the diameter difference D-d causes the shaft sleeve  40  to be pressed against the shoulder  52  of the rotary shaft  50 . 
   The seal cover  30  engages the housing  60  and is retained within the housing  60  by fixedly connecting a flange  70 A of a retainer ring  70  to the housing  60  by means of screw bolts  71 . Disposition of the seal cover  30  can be achieved by holding the right side end face of the cover  30  by the retainer ring  70  as seen in the figure, and does not require the left side end face of the cover  30  to be engaged by a step shoulder. This relation holds from the aforementioned relationship of counter pressures one of which is the pressure exerted to the back face  5  of the stationary seal ring  3  and the other of which is the pressure exerted onto the end face  42 . 
   Intermediate chamber B is disposed between a pair of the seal parts  20 A and  20 B and the mechanical shaft seal  2  for the inner diameter surface of the seal cover  30  which fits over the housing  60 . A drain passage  38  disposed in the seal cover  30  is a through hole connected to the intermediate chamber B. The drain passage  38  is directly connected to a drain hollow  62  via an annular cavity  34 . A device to process hazardous gases such as ethylene gas or propylene gas is disposed at the outlet of the drain hollow  62 . Pressure of the intermediate chamber B is set lower than that of a sealed fluid chamber A. 
   Furthermore, a circulation passage  32  is disposed in the seal cover  30  so as to cool off the mechanical shaft seal  2  by circulating the fluid such as oil from the sealed fluid chamber A. The circulation passage  32  is directly connected to a passage hollow  61  via an annular cavity  33 . A dam  58  is disposed in the outer circumferential region of the mechanical shaft seal  2  to circulate along the sealing face  6  of the mechanical shaft seal  2  and the mating sealing face  16 . The seal cover  30  and the retainer ring  70  are connected by screw bolts  72 . 
   Buffer fluid passage  37  disposed in the seal cover  30  directly connects the buffer fluid chamber C and a buffer fluid hollow  63  via an annular cavity. Pressure of the buffer fluid chamber C is set higher than that of the intermediate chamber B. 
   As a consequence, a relation of the internal pressures of the sealed fluid chamber A, the intermediate chamber B, and the buffer fluid chamber C is represented by A&gt;B and C&gt;B. Therefore, the sealed process fluid is ejected from the drain passage  38  without leaking through the first seal part  20 A and the second seal part  20 B disposed in the buffer fluid chamber C. Fluid leaked from the sealed fluid chamber A also is ejected from the drain passage  38 . 
   Next described is another form of a preferred embodiment in accordance with the present invention. 
   A mechanical seal device  1  as a second preferred embodiment of the present invention is to seal a sealed process fluid by being disposed between the inner circumferential surface of a housing  60  and a rotary shaft  50  retained inside the inner circumferential surface of the housing, being comprised of a mechanical shaft seal  2 , a buffer fluid chamber C, seal parts  20 A,  20 B, and an intermediate chamber B, the mechanical shaft seal  2  being disposed between the housing  60  and a shaft sleeve  40  fitted over the rotary shaft  50  so as to seal the sealed process fluid, the buffer fluid chamber C being constructed between the housing  60  and the shaft sleeve  40  in the opposite side of the sealed fluid region with respect to the mechanical shaft seal  2  and being connected to a buffer fluid passage  37 , the seal parts  20 A,  20 B to seal a gap between the shaft sleeve  40  and the housing  60  inside the buffer fluid chamber C, the intermediate chamber B being disposed between the mechanical shaft seal  2  and the seal parts  20 A,  20 B and being connected to a drain passage  38 , the buffer fluid pressure inside the buffer fluid chamber C being set higher than the fluid pressure inside the intermediate chamber B. 
   The mechanical seal device  1  as the second preferred embodiment of the present invention can prevent a sealed process fluid inside the intermediate chamber B from leaking to an atmospheric region because of the pressure inside the buffer fluid chamber C being set higher than the pressure of the intermediate chamber B. 
   A mechanical seal device  1  as a third preferred embodiment of the present invention is constructed in such a way that the pressure of a sealed process fluid is lower than the fluid pressure in an intermediate chamber B while the pressure in an intermediate chamber B being higher than the fluid pressure in a buffer fluid chamber C. 
   In the mechanical seal device  1  as the third preferred embodiment of the present invention, even if the seal of the mechanical shaft seal  2  is broken, a harmful sealed process fluid is effectively prevented from leaking to an atmospheric region by being ejected from the intermediate chamber B to a collecting device through a drain passage  38  because of the pressure inside the intermediate chamber B being set lower than the pressure of the sealed fluid chamber A. 
   A mechanical seal device  1  as a fourth preferred embodiment of the present invention has a disconnectable snap ring disposed near the end face of a shaft sleeve to engage a split seal cover for retaining seal parts and the snap ring is removed after the mechanical seal device is installed to the shaft sleeve. 
   In the mechanical seal device  1  as the fourth preferred embodiment of the present invention, the shaft sleeve does not require fitting devices for retaining respective seal parts, therefore the sleeve  40  can be made light and slim. Furthermore, a rotary shaft and the sleeve do not need to fit over each other in an atmospheric region, therefore the rotary shaft can be made small in diameter. Consequently, the reduction in weight makes it possible for the rotary shaft to rotate fast. Also energy consumption can be saved for driving the rotary shaft. 
   Mechanical seal devices in accordance with the present invention are expected to be able to effective in the following merits. 
   In a mechanical seal device  1  in accordance with the present invention, a sealed process fluid exerts more pressure to the back face of a stationary seal ring  3  than to the end face  42  of a shaft sleeve  40 , therefore the sleeve  40  can be engaged to a shoulder  52  of a rotary shaft  50 . Accordingly, the sleeve  40  does not require a fitting device for fixing and thinning the wall thickness of the sleeve results in a reduction in weight. As a consequence, omitting fitting devices and thinning the sleeve  40  yields a reduction in the total size of the mechanical seal device. The reduction in weight then makes it easy for the mechanical seal device  1  to undergo a high speed rotating motion 
   In addition, leakage of the sealed process fluid from the intermediate chamber B to the atmospheric region can be prevented due to the fact that the pressure inside the buffer fluid chamber C is set higher than the pressure of the intermediate chamber B. 
   Even in the case of a seal failure of the mechanical shaft seal  2 , since the pressure of the intermediate chamber B is lower than the pressure of the sealed fluid chamber A, the leaked hazardous fluid is effectively caught and ejected from the intermediate chamber B to a collection device through the drain passage  38  without leaking to the atmospheric region HP 
   Having described specific embodiments of the invention, however, the descriptions of these embodiments do not cover the whole scope of the present invention nor do they limit the invention to the aspects disclosed herein, and therefore it is apparent that various changes or modifications may be made from these embodiments. 
   The technical scope of the invention is specified by the claims.

Technology Classification (CPC): 5