Abstract:
A shutoff device for shutting off liquids or gases comprises a device housing ( 10 ) and a device ( 13 ) movable in said housing ( 10 ), the device ( 13 ) being provided with an opening ( 14 ). For sealing purposes, annular sealing bodies ( 28 ) are provided which are supported in annular fluid cylinders ( 27 ). The contact surfaces ( 34 ) are coated with a hard-material layer ( 37,39 ) which is subjected to microfinishing. The sealing bodies ( 28 ) are yieldingly supported such that they are capable of following any deformation or displacement of the device ( 13 ). The sealing is particularly suitable for aggressive and abrasive media and solids-carrying media.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a shutoff device for shutting off conduits, said device comprising a device housing having a passage, and a device movable within said housing. 
   Shutoff devices serve for shutting off fluid-carrying conduits. The fluids may be gases, liquids, solids and in particular multiphase systems where e.g. solids are transported together with a gaseous or liquid carrier medium. All these materials have a wide spectrum. For example, solids ranging from granular and abrasive products to logs or stones may be transported through the conduit. The liquids and gases may be aggressive substances, e.g. an acid or any type of waste water. Further, the sizes of shutoff devices may vary within a wide range. A characteristic dimension is the diameter of the passage and/or the adjacent conduits. Frequently, the diameter has a size of approximately 40 cm. 
   In the device housing of a shutoff device the device is linearly movable in a guideway to be moved from the open position into the closed position. This adjustment is normally effected pneumatically or hydraulically or by means of a motor. In each of these two positions the device must be sealed towards the passage to prevent the medium from uncontrolledly escaping at the shutoff device. Normally, the device is sealed by means of annular soft seals. These seals are made of graphite, PTFE filled with graphite (Manoy) or electrocoal. Such seals are rapidly destroyed by problematic media, i.e. by mechanical action, such as abrasion, or chemical or thermal action. Although the seals are arranged at a distance to the circumference of the passage they are exposed to the medium. 
   For improving the seals, shutoff devices have been developed which are provided with fluid cylinders in the device housing, said fluid cylinders including annular sealing bodies. Each sealing body is provided with a soft seal at the surface facing the device, said soft seal pressing against the device. This is designed to compensate for any wear of the soft seals, and it is ensured that the annular pistons are always pressed with an adequate pressure force against the device. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide a shutoff device which does not show essential wear and whose tightness does not decrease even when it is exposed to problematic fluids. In other words, it is an object of the invention to prolong the service life of the seal. 
   This object is achieved with the features of claim  1 . Accordingly, sealing is provided between rigid sealing bodies which are included in the fluid cylinders and supported by the fluid, and the device, wherein the cooperating contact surfaces are provided with a hard-material layer which is harder than the device material and whose surface has a roughness of less than 10 μm. This means that the sealingly abutting surfaces have a large hardness and a large evenness such that they snugly bear against each other without any inclusions. This hard-material seal is used in combination with yieldingly pressing the sealing bodies against the device. This means that the device is allowed to move transversely to the device plane or to deform without the sealing action being affected. This movability is due to the fact that the annular sealing bodies are configured as pistons to which either a gas (compressed air) or a liquid is applied. When a liquid is applied, a gas pressure storage means is to be provided because of the incompressibility of the liquid in order to attain the necessary yielding capability of the pressure force. 
   The hard-material layer is preferably made from a ceramic-bonded or metal-bonded carbide or oxide. Such hard-material coatings are known per se and need not be explained in detail. For example, silicon carbide or silicon oxide are suitable materials. 
   The surface roughness of the hard-material layers is preferably smaller than 2 μm and in particular smaller than 0.4 μm. The small surface roughness is attained, after application of the hard-material layer, by microfinishing, in particular by honing or lapping, where microfinishing is carried out in pairs with the surfaces to be finished rubbing against other such that an exact mutual matching over the entire surface is achieved, wherein however only these two individual surfaces fit together and produce the necessary sealing action. 
   According to a preferred embodiment of the invention it is provided that the contact surface of the device has a width in the direction of movement of the device, which is smaller than that of the sealing body, with the remaining area of the surface facing the device being arranged somewhat to the rear. In this manner it is realized that the sealingly abutting surfaces are only as wide as necessary and do not extend over the overall width of the wall of the annular sealing body. Further, foreign matter is forced out of the area of the sealing surfaces. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Hereunder an embodiment of the invention is explained in detail with reference to the drawings in which: 
       FIG. 1  shows a cross-section of the shutoff device, 
       FIG. 2  shows a view of the shutoff device in the direction indicated by arrow II of  FIG. 1 , 
       FIG. 3  shows an enlarged representation of detail II of  FIG. 1 , 
       FIG. 4  shows an enlarged representation of detail IV of  FIG. 3 , and 
       FIG. 5  shows a front view of the device. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The shutoff device shown comprises a housing  10  composed of two housing halves  10   a , 10   b  which axially bear against each other and are screwed to each other. The housing halves are provided with bores aligned with each other and forming a passage  11 . At each end of the housing halves a flange  12  is provided for flange-mounting a conduit. Between the housing halves an elongate cavity is formed in which a plate-shaped device  13 , which is provided with an opening  14  of approximately the same size as the passage  11 , is adapted to be displaced transversely to the axial direction of the housing. The housing  10  comprises, in the plane of the device  13 , two receiving spaces  15 ,  16  extending to opposite sides, one of the receiving spaces being capable of accommodating one half of the device  13  while the other half is located within the housing  10 . At the outer end of the receiving space  16  a pneumatic cylinder  18  is fastened via rods  17 , said cylinder including a piston  19 . The pneumatic cylinder is controlled by a valve  20  which is connected to a compressed air source (not shown). To the piston  19  a piston rod  21  is connected which extends into the end of the receiving space  16  and is connected at its other end with the device  13 . The passage of the piston rod  21  through the end wall  22  of the receiving space  16  is sealed with the aid of a stuffing box packing  23 . 
   In the present embodiment, the receiving spaces  15 , 16  are provided with shielding walls  24  to protect the walls of the shutoff device against heat radiation. 
     FIG. 1  shows the device  13  in its shutoff position in which the opening  14  is located in the receiving space  15 , while the housing  10  includes the closed plate region of the device  13  which shuts off the passage  11 . In this closed position the piston rod  21  is moved out of the pneumatic cylinder  18 . If the device  13  is to be moved into the open position, the piston  19  is retracted in the cylinder  18  such that the opening  14  of the device  13  extends coaxially to the passage  11 . 
   The passage  11  between the housing  10  and the device  13  is sealed by two annular seals  25 , 26  each of which is included in one housing half  10   a , 10   b . For this purpose, each housing half comprises an annular fluid cylinder  27  ( FIG. 3 ) which is configured as an axial groove in the housing half. Each fluid cylinder  27  includes an annular rigid sealing body  28  which forms an annular piston. The annular pistons  28  surround the passage  11  on each side of the device  13 . Each sealing body  28  comprises on its inside two sealing rings  29  and on its outside two sealing rings  30  adapted for sealing towards the pneumatic annular fluid cylinder  27 . At the outer end  31  a pressure line  32  and  33 , respectively, extends into each fluid cylinder  27  to advance the sealing body  28  towards the device  13 . 
   Each sealing body  28  comprises, on the side facing the device  13 , a contact surface  34 . This surface is narrower than the width of the sealing body and merges via an inclined shoulder  35  with an area  36  arranged somewhat to the rear. The contact surface  34  shaped as an annular disk is located at the sealing body  28  at the end adjacent to the the passage  11 , while the area  36  is located remote from the passage. 
   The contact surface  34  is coated with a hard-material layer  37  which extends over a portion of the inclined shoulder  35 . 
   The device  13  is on each of its two sides provided with two hard-material layers  38 , 39  ( FIG. 5 ). These hard-material layers  38 , 39  are shaped as annular disks. One of the hard-material layers  38  is arranged around the opening  14  of the device  13 , and the other hard-material layer  39  is arranged around the closing surface of the device, which is located inside the passage  11  of the housing when the device is in the closed position, as shown in  FIGS. 1 and 2 . 
   The hard-material layers  37 , 38 , 39  are preferably made from ceramic material, such as chromium dioxide, or from hard metal, such as tungsten carbide. Subsequent to their application, the layers are subjected to microfinishing, i.e. first to grinding and then to honing or lapping. The roughness amounts to max. Ra 4 which corresponds to 4 μm. In particular, the roughness amounts to approximately Ra 0.4, i.e. 0.4 μm, and less. The width of the contact surface  34  amounts to less than 10 mm, and in particular to approximately 5 mm. The width should not be larger than required for producing the sealing action. 
   Microfinishing of the surfaces of the hard-material layers is carried out by lapping in pairs, wherein two hard-material layers are placed one upon the other and rubbed against each other. These two hard-material layers are those of the device  13  and the associated sealing body. Those hard-material layers which are adapted to later sealingly bear against each other are finished by being rubbed against each other such that the hard-material layers fit together in pairs. 
   Pressure application to the sealing bodies  28  is effected from the cylinder  18 . From the control valve  20  a line  40  extends to the rear end of the cylinder  18 . This line serves for generating in the cylinder  18  a force acting upon the piston  19 , said force driving the device  13  into the closed position. The line  40  is connected via further lines  41 , 42 , 43  with a distributor  44  to which the lines  32  and  33  are connected. When pressure is applied to the cylinder  18 , first the device  13  is moved into the closed position, and subsequently the sealing bodies  28  are pressed against the device from opposite sides. This pressing is effected in a yielding manner. This means that the sealing bodies  28  follow any deformation or displacement of the device with the sealing action being maintained. 
   Another line  45 , which extends from the valve  20  into the front end of the cylinder  18 , serves for setting the piston  19  into the retraction position, whereby the device  13  is moved into the open position. 
   The shutoff device according to the invention is suitable for use in conjunction with aggressive and abrasive media and for use at high temperatures. The edge of the opening  14  can be configured as a blade such that any foreign matter, which gets stuck when the device is in the open position, is cut up when the device is moved. Such a blade need only be present at the half of the device opening  14  facing the cylinder  18 , while the other half may be of blunt configuration. 
   Although a preferred embodiment of the invention has been specifically illustrated and described herein, it is to be understood that minor variations may be made in the apparatus without departing from the spirit and scope of the invention, as defined by the appended claims.