Abstract:
A discharge valve is disclosed which includes a valve housing which can be functionally connected to a process element having a pressurized interior space. The valve housing includes a flow channel having a longitudinal center axis (A) and is in working cooperation with a valve member. The flow channel is arranged to be in fluid communication with the pressurized interior space in the process element after the discharge valve has been connected to the process element. The valve member is displaceable between an open position and a closed position in a displacement direction (B) whereby the discharge valve can be opened and closed. The flow channel comprises a detachable inner lining having an envelope wall, and the detachable inner lining comprises an aperture extending through the envelope wall and through which the valve member is adapted to run when being displaced between the opened and closed positions.

Description:
TECHNICAL FIELD 
       [0001]    The invention pertains to a discharge valve, in particular a discharge valve for use in a manufacturing process involving processing of lignocellulosic material, such as a pulp manufacturing processes or a process for manufacturing bio fuel. The discharge valve comprises a valve housing which is connectable to a process element having a pressurized interior process volume. The valve housing comprises a flow channel which is in working cooperation with a valve member, and which is arranged to be in fluid communication with the pressurized interior process volume of the process element after the discharge valve has been connected to the process element. The valve member is arranged to be displaced in the flow channel in a displacement direction at an angle to a longitudinal centre axis of the flow channel, such that the valve member can be moved between a fully open position and a fully or partially closed position along the displacement direction. 
       BACKGROUND 
       [0002]    In the process industry and, in particular, in the biomass process industry such as in pulp manufacturing and in the manufacturing of bio fuels, discharge valves are used to control the pressure and/or process flow in process elements such as boilers, reactors and refiners which have inner pressurized process chambers. Shutter valves, gate valves and ball sector valves are the most commonly used types of discharge valves in the pulp manufacturing industry. The process flows in a process involving processing of lignocellulosic materials are generally corrosive, of a high temperature and with a high content of abrasive particulate material such as cellulose fibers and fragments and impurities following with the processed material. Consequently, a discharge valve being continuously exposed to a pressurized flow of hot, abrasive and corrosive material will wear out over time and will have to be replaced by a new valve. This is costly and, in addition, involves lengthy stop-times in the process as the process will have to be interrupted while the process equipment cools down and is cleaned so that the worn-down discharge valve can be disconnected from all couplings and a new discharge valve can be mounted in the place of the discarded valve. 
         [0003]    It is therefore an object of the invention to provide a discharge valve having a more robust construction and longer service life. A further object of the invention may be to reduce process stop-times caused by valve maintenance. Yet another object may be to offer a discharge valve having greater versatility than previously used discharge valves. 
       SUMMARY 
       [0004]    According to the invention, there is offered a discharge valve, in accordance with claim  1 . Further embodiments are set out in the dependent claims. 
         [0005]    The discharge valve as disclosed herein comprises a valve housing which is connectable to a process element, the process element having a pressurized interior process volume. The discharge valve comprises a flow channel having a longitudinal centre axis, A, and being in working cooperation with a valve member, the flow channel being arranged to be in fluid communication with the pressurized interior process volume of the process element after connection thereto. The valve member comprises an insertion part which is insertable in the flow channel by displacement of the valve member in a displacement direction, B, at an angle, α, to the longitudinal centre axis, A. 
         [0006]    The flow channel is at least partly formed by a detachable inner lining having an envelope wall, wherein the detachable inner lining comprises an aperture extending through the envelope wall and through which opening the valve member is adapted to run when being displaced in the displacement direction, B. 
         [0007]    The discharge valve as disclosed herein may be a discharge valve adapted for connection to an outlet of a pressurized process element in any biomass processing system involving evacuation of material from pressurized processing voids, such as found in refiners, boilers and reactors or may be a discharge valve connected to an outlet of a pressurized process element in any biomass processing system involving evacuation of material from pressurized processing voids, such as found in refiners, boilers and reactors. Biomass processing systems may be found e.g. in cellulose pulp manufacturing processes and in bioplants for the production of biofuels such as ethanol and biodiesel. Such processes involve processing lignocellulosic raw materials derived from perennial plants such as trees as well as annual plants such as sugar cane, straw, hemp, etc. 
         [0008]    The detachable inner lining as disclosed herein may have a generally tubular shape with an inner envelope wall surface defining the shape of the flow channel in the discharge wall and an outer envelope wall surface which is arranged to face the valve housing and which is adapted to cooperate with the valve housing when attaching the detachable inner lining in the valve housing. As used herein, an element having a tubular shape is an elongate, hollow element having an inner longitudinally extending channel and an outer wall surrounding the inner channel. The tubular element may have any cross-sectional shape, such as square, rectangular, circular, etc. The cross-sectional shape of the tubular element may vary along the length of the element. 
         [0009]    The detachable inner lining is arranged to be removed from the valve housing and may be arranged to be reattached to the valve housing and/or to be replaced by another detachable inner lining. The discharge valve is arranged to be coupled to a process element at an inlet end of the discharge valve. The discharge valve may be directly coupled to the process element or may be indirectly coupled to the process element by being placed downstream of the process element in a feed system with one or more intervening pipe sections between the discharge valve and the outlet from the pressurized process element. The inlet end of the discharge valve is the end of the discharge valve which will be directed towards the outlet from the pressurized process element when the discharge valve is coupled to the pressurized process element. The inlet end of the discharge valve is the end through which the pressurized process flow which may contain fibres, particles and corrosive components will enter the discharge valve. When the discharge valve is in use, the detachable inner lining forming the flow channel will gradually be worn away. Depending on the flow profile through the discharge valve, the inner wall of the detachable inner lining will be exposed to uneven wear. The size of the flow through the flow channel may be regulated by moving the insertion part of the valve member into the flow channel so that the cross-sectional area of the flow channel is diminished by the valve member. During normal operation of the discharge valve, a portion of the insertion part of the valve member will be located in the flow channel and will be hit by the process flow, causing the process flow to be deflected towards the wall of the detachable inner lining downstream the valve member. This means that the parts of the discharge valve which are most exposed to mechanical wear and corrosion caused by the process flow are the upstream side of the insertion part of the valve member and the part of the inner wall of the detachable inner lining which is located downstream of the valve member and which faces towards the end surface of the valve member. Accordingly, the most wear of the inner lining will generally be found directly after the valve member or throttle. 
         [0010]    By providing the discharge valve with a detachable inner lining, it has been found that the useful life of the discharge valve may be considerably extended by merely replacing a worn-down detachable inner lining with a new detachable inner lining without having to replace the whole discharge valve. 
         [0011]    It may be preferred that the detachable inner lining has a symmetrical shape allowing the detachable inner lining to be detached from the flow channel, turned back-to-front, and inserted again into the valve housing. In other words, the detachable inner lining may have an end-to-end shape such that it can be taken out of the valve housing, be rotated 180 degrees about an axis perpendicular to the longitudinal centre axis, A, and be reattached in the valve housing in the new direction. By designing the detachable inner lining such that it can be applied in the valve housing with any one of the two opposing ends of the detachable inner lining at the inlet end of the discharge valve, the working life of the detachable inner lining may be considerably extended as different parts of the detachable inner lining may be exposed to wear during use of the discharge valve. When the end of the detachable inner lining which is initially placed at the outlet end of the discharge valve has been worn down, the detachable inner lining can be removed from the valve housing, turned around and inserted with the opposite non-worn end placed at the outlet end of the discharge valve. 
         [0012]    The discharge valve as disclosed herein may be arranged to be adapted to different process demands by selecting a detachable inner lining adapted to the particular process conditions at hand. Accordingly, a range of detachable inner linings may be provided with inner linings having been designed with particular regard to one or more process conditions. Accordingly, the inner linings may be provided with one or more of high temperature resistance, chemical resistance, wear resistance etc. It is further possible to provide inner linings having flow channels of different sizes and/or different shapes. By offering a wide selection of inner linings, the discharge valve as disclosed herein may easily be adapted to process flows of different compositions and/or different flow rates. 
         [0013]    The envelope wall of the detachable inner lining constitutes a replaceable inner wear surface in the discharge valve. For a given lining material, the greater the thickness is of the envelope wall of the detachable inner the higher is the wear resistance and thereby the longer is the service life of the detachable inner lining. The envelope wall of the detachable inner lining may have a thickness of from 2-100 mm, preferably from 5-80 mm, more preferably from 10-50 mm. The envelope wall thickness can be 5, 10, 15, 20, 25, 30, 35, 40 or 45 mm, for example. 
         [0014]    The inner lining of the discharge valve as disclosed herein may have an inner diameter and the insertion part of the valve member may have a diameter, wherein the inner diameter of the detachable inner lining is smaller than the diameter of the insertion part of the valve member. 
         [0015]    The flow channel which is defined by the inner diameter of the detachable inner lining may have a diameter ranging from 5 mm for small scale processes such as laboratory scale processes up to 300 mm for large scale processes. The inner diameter of the detachable inner lining may preferably be from 30-200 mm. An inner diameter of the detachable inner lining can be 50, 60, 70, 80, 90, 100, 110, 120, 130 or 140 mm, for example. As set out herein, the inner diameter of the detachable inner lining and thereby the diameter of the flow channel may vary along the longitudinal axis A. The inner diameter of a detachable inner lining or of a part of a detachable inner lining having a non-circular cross-section is the diameter of the largest circle which can be inscribed within the cross-sectional area of flow channel. 
         [0016]    The discharge valve as disclosed herein is a throttle valve and the valve member or throttle may be a plunger which is inserted into the flow channel at an angle, α, to the flow channel to fully or partly close the flow channel. In the first instance, after insertion of the valve member into the flow channel, the flow in the flow channel will be completely blocked while a partly inserted valve member will only serve as a throttle and restrict the flow in the flow channel. The valve member is moved into and out of the flow channel in the displacement direction, B, which is arranged at the angle, α, with respect to the longitudinal centre axis, A, of the flow channel, wherein the angle, α, may be from 30-150 degrees, preferably from 45-135 degrees, more preferably from 80-100 degrees, and most preferably 90 degrees or substantially 90 degrees. 
         [0017]    As set out herein, the valve member may have the form of a cylindrical body, as a cylindrical rod or tube, wherein the cylindrical body preferably has a circular cross section. A cylindrically shaped valve member may be preferred as it provides better sealing of the flow channel than other types of valve members. The valve member is preferably solid at least in the insertion part of the valve member which is positioned in the flow channel when the valve member is in the closed position or in a throttle position. This is the part of the valve member which will be most exposed to wear during use of the discharge valve. A solid valve member provides better wear resistance than a non-solid valve member and will have a longer service life than a non-solid valve member. The valve member may be a replaceable part of the discharge valve and/or may be arranged such that it can be rotated to expose different surfaces to wear from a process flow. Rotation may be arranged to be carried out manually or by means of a motor. Here it should be appreciated that such rotational movement of the valve member, to expose different surfaces thereof to wear from a process flow, is independent of moving the valve member into and out from the flow channel. 
         [0018]    The detachable inner lining may comprise a mating surface and the valve member may be adapted to be positioned such that it abuts the mating surface of the detachable inner lining when the valve member is in a fully closed position. Accordingly, the mating surface may be configured such that it will mate with a corresponding mating surface arranged at an outer end of the insert part of the valve member and thereby form a closure between the envelope wall of the detachable inner lining and the outer end of the valve member. 
         [0019]    The mating surface on the detachable inner lining may be formed by a recess in the envelope wall of the detachable inner lining and may be a recess having a circular periphery corresponding to a circular periphery of the end of the insert part. The recess and the end of the insert part may have a curvature in order to conform to an inner curvature of the valve housing and/or the detachable inner lining. 
         [0020]    An adequate closure between the outer end of the insert part of the valve member and the inner lining may be obtained without a recess in the envelope wall of the detachable inner lining by only providing the outer end of the valve member with a profiled surface matching a profile of the inner surface of the detachable inner lining. By way of example, if the inner lining has an inner surface with a circular cross section, the valve member may be provided with a correspondingly curved outer end. 
         [0021]    In the discharge valve as disclosed herein, the valve member may be arranged such that it can be displaced out of the flow channel, to a position in which it is clear from the detachable inner lining. This means that the valve member may be moved in the displacement direction, B, until it is not only completely retracted from the flow channel but moved away from the flow channel in the displacement direction, B, at least a further distance corresponding to the thickness of the envelope wall of the detachable inner lining. By positioning the valve member in the fully retracted service position, where it is clear from the detachable inner lining, the detachable inner lining can be removed from the valve housing without needing to completely disassemble the discharge valve. 
         [0022]    The described discharge valve may be particularly useful when discharging from pressurized interior spaces, such as pressurized chambers, such as during a steam explosion pulp manufacturing process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The present invention will be further explained hereinafter by means of non-limiting examples and with reference to the appended drawings wherein: 
           [0024]      FIG. 1  shows a refiner and a discharge valve according to an embodiment of the present invention; 
           [0025]      FIG. 2  shows a cross sectional view of the discharge valve of  FIG. 1 , with a valve member being in a fully open position. 
           [0026]      FIG. 3  shows a discharge valve in a partly opened position with a valve member positioned between a fully open position and a completely closed position. 
           [0027]      FIG. 4  shows a discharge valve with a valve member in a completely closed position; 
           [0028]      FIG. 5  is a cross sectional view of a discharge valve showing detachable inner lining in greater detail; and 
           [0029]      FIG. 6  shows a cross sectional view of a discharge valve  23  in a service position. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    It is to be understood that the drawings are schematic and that individual components, are not necessarily drawn to scale. The discharge valve shown in the figures is provided as an example only and should not be considered limiting to the invention. Accordingly, the scope of the invention is determined solely by the appended claims. 
         [0031]    Although described as implemented in connection to refiner in a pulping process, the teachings of the current disclosure are equally applicable to other systems (hot or cold) in which abrasive material is evacuated from a pressurized process chamber into a pipe, open air or into another process chamber. As the abrasiveness of a material depends on both the material itself as well as the surrounding environment, the term abrasive is used to describe the processing of a material in which process the material can be regarded as abrasive. As an example, at a low temperature a material might not be viewed as being abrasive whereas at a higher temperature, the abrasive wear of the material is clearly increased. 
         [0032]    A general system in which the present disclosure can be beneficial implemented may include a pressurized process space such as a process chamber or container into which material is introduced at one end and subjected to e.g. boiling, steaming or other hot or cold process. The material is transported within the processing chamber and evacuated at an outlet in another end of the chamber. The evacuated material is then transported through a system of pipes to subsequent processing arrangements. The teachings of the current disclosure are beneficially implemented at the outlet of the pressurized processing chamber. Examples of such a pressurized processing container include a boiler, steamer, refiner for pulp, impregnator, vertical or horizontal reactors, etc. 
         [0033]      FIG. 1  shows a refiner  10  for a pulp manufacturing process and specifically a mechanical pulping process. Generally wood chips are washed, pre-treated with heat and/or a chemical pretreatment and refined to pulp. The wood chips are fed between two disks in a refiner, such as the refiner  10  having an interior process volume  11 , wherein the wood chips are ground to pulp. A discharge valve  20  is connected to an outlet  12  of the refiner  10 . During processing in the refiner  10 , pressure and heat are built up putting the discharge valve  20  under a lot of strain and wear as the discharge valve  20  is opened and pressurized pulp is discharged through the discharge valve  20 . The discharge valve  20  will be described in greater detail below. 
         [0034]      FIG. 2  shows a cross sectional view of the discharge valve  20  when the discharge valve  20  is in a fully open position.  FIG. 2  shows a valve housing  21  comprising a flow channel  22  through which the pressurized pulp suspension can flow in a first flow direction indicated by the arrow in  FIG. 2  when the discharge valve  20  is opened. The flow channel  22  has a longitudinal centre axis A. A valve member  23 , shown in a retracted position where the flow channel  22  is completely unrestricted by the valve member  23  is arranged along a displacement direction indicated by the arrow B in  FIG. 2  to thereby provide a valve function to the discharge valve  20 . 
         [0035]    A detachable inner lining  25  is applied inside the valve housing  21  and defines the shape and size of the flow channel  22 . The detachable inner lining  25  is detachable in the sense that it can be removed from the valve housing  21  without destroying or damaging the valve housing  21 . The detachable inner lining  25  is thus intended to be replaceable, the valve housing  21  is thus adapted to have a replaceable detachable inner lining  25 . The detachable inner lining  25  can be replaced by another detachable inner lining, or the detachable inner lining  25  can be inserted back again, e.g. after having been turned back-to-front. The detachable inner lining  25  can be press fitted into the valve housing  21 , or be attached by other means such as via brackets and/or screws (not shown). A further alternative is that the detachable inner lining  25  is fixed in position by flange connections connecting the discharge valve to other elements in the process equipment such as pipes, a process chamber outlet, etc. 
         [0036]    The detachable inner lining  25  as shown in the figures, has a circular cross section formed by an envelope wall  25  having a thickness T. Other cross-sectional shapes may alternatively be used, as set out herein. The detachable inner lining  25  can be said to have a generally tubular shape with an inner envelope wall surface  25 ′ which defines the shape of the flow channel  22 . As set out herein, a suitable envelope wall thickness can be from 2-100 mm, preferably from 5-80 mm, more preferably from 10-50 mm. In the shown embodiment, the envelope wall thickness is 30 mm. The length of the flow channel  22  is defined between an inlet end  27  and an outlet end  28 . In the drawings, the length of the detachable inner lining  25  is shown to correspond to the length of the flow channel  22  of the valve housing  21 . Alternatively, the length of the detachable inner lining  25  does not have to be exactly the same length as the length of the flow channel  22  in the valve housing  21 . Accordingly, the inner lining  25  can be shorter or longer than the flow channel  22  of the valve housing  21 . It may generally be preferred that the inner lining  25  has a length which is at least 90% of the length of the flow channel  22  in the valve housing  21  in order to adequately protect the inner wall of the valve housing  21  from wear during use. The detachable inner lining  25  has an inner diameter Di defining the diameter of the flow channel  22 . As set out herein, the inner diameter Di of the detachable inner lining  25  can be from 5 to 300 mm, preferably from 30-150 mm. The inner diameter of the detachable inner lining  25  is in the shown embodiment 70 mm. 
         [0037]    As is noticeable in  FIG. 2 , the detachable inner lining  25  is provided with an aperture  30  through which an insertion part  24  of the valve member  23  is inserted into the valve housing  21 . The aperture  30  extends through the wall of the valve housing  21  and through the whole thickness of the envelope wall  26  of the detachable inner lining  25 . The aperture is further aligned with the displacement direction B as indicated in  FIG. 2  in order to allow the valve member  23  to be moved between a completely closed position as illustrated in  FIG. 4 , an intermediate throttle position as representatively illustrated in  FIG. 3 , and optionally a service position as shown in  FIG. 6 . 
         [0038]    The detachable inner lining  25  may be made from a wear resistant material such as steel and preferably high strength and wear resistant steel. 
         [0039]    The insertion part  24  of the valve member  23  in the shown example has the form of a generally cylindrical body  40  having a circular cross section with a diameter Dcb. As set out herein, the insertion part  24  of the valve member  23  may have any suitable cross-sectional shape. The aperture  30  through the valve housing  21  into the flow channel  22  should be sized and shaped such that the insertion part  24  of the valve member  23  can be inserted into the flow channel  22  through the aperture and be moved into and out of the flow channel  22  in the displacement direction B. It may be preferred that the aperture  30  is sized and configured such that the insertion end  24  of the valve member  23  fits snugly in the aperture  30 . 
         [0040]    The displacement direction B of the valve member  23  extends perpendicular to the longitudinal axis A of the flow channel  22 . It should be noted that the displacement direction B forms an angle α to the longitudinal centre axis A of the flow channel  22 , as indicated in  FIG. 2 . In the embodiment shown in the figures, the angle α is 90°, i.e. the valve member  23  is moved in the displacement direction B perpendicular to the longitudinal centre axis A of the flow channel. Alternatively, the valve member  23  may inserted through the housing wall with a tilt, implying that the angle α between the displacement direction B and the longitudinal centre axis A of the flow channel  22  deviates from a 90° angle. If the displacement direction B of the valve member  23  is tilted, the aperture  30  of the envelope wall of the detachable inner lining  25  needs to be adjusted accordingly. As set out herein, the angle α may be from 30-150 degrees, such as from 45-135 degrees, preferably from 80-100 degrees and more preferably 90 degrees or substantially 90 degrees. 
         [0041]    The valve member  23  is a wear component of the discharge valve  20  as disclosed herein and is preferably a solid body, such as a solid cylindrical body, as shown in  FIG. 2 . At least the insertion part  24  of the valve member  23  which during use of the discharge valve  20  may intersect with the flow channel  22 , as illustrated in  FIGS. 3 and 4 , is preferably solid. It should be noted that a solid body can have an attachment portion  41  for attaching the valve member  23  to a drive, such as an electrical motor  42 , which is arranged to displace the valve member  23  in the displacement direction B. 
         [0042]    As the valve member  23  is a part of the discharge valve  20  which highly exposed to wear during use of the discharge valve  20 , it may be preferred that the valve member  23  or at least the insertion part  24  of the valve member can be removed from the valve arrangement and replaced with a new valve member  23  or insertion part  24 . The whole valve member  23  or only the insertion part  24  may be arranged such that it can be rotated about its own longitudinal axis either continuously during operation or during maintenance so as to provide a fresh surface towards the fluid flow which has not been subjected to wear. By rotating the insertion part or the whole valve member so that different parts of the valve member is exposed to the abrasive process flow in the flow channel  22 , the life span of a specific valve member  23  can be prolonged and the valve member does not need to be replaced as frequently. 
         [0043]      FIG. 3  shows the valve member  23  in a partly opened position or a throttle position with the insertion part  24  of the valve member  23  inserted into the flow channel  22  to approximately 50% of the available distance. When in a throttle position, the cross-sectional area of the flow channel  22  is reduced by the valve member  23 , thus causing a restriction in the flow path in the flow channel  22 . The 50% throttle shown in  FIG. 3  is only intended as an illustrative example and it should be understood that the end surface  43  of the insertion part  24  may be located at any level inside the flow channel  22 . 
         [0044]    During normal operation of the discharge valve  20 , when the flow channel  22  is partly blocked by the insertion part  24  of the valve member  23 , the process flow will enter the flow channel  22  from the inlet end  27  in the flow direction indicated by the arrow F. When the process flow reaches the inserted part  24  of the valve member  23 , it will impinge on the valve member  23  and be deflected towards the envelope wall  26  of the detachable inner lining  25  downstream the valve member  23 . This means that the parts of the discharge valve  20  which are most exposed to mechanical wear and corrosion caused by the process flow are the upstream side of the insertion part  24  of the valve member  23  and the part of the envelope wall  26  of the detachable inner lining  25  which is located downstream the valve member  23  and which faces towards the end surface  43  of the valve member  23 . Accordingly, the most wear of the inner lining  25  will generally be found directly after the valve member  23  or throttle. When the valve member  23  is in the throttle position shown in  FIG. 6 , the areas in the flow channel  22  which are most exposed to wear are the lower upstream end area  60  of the insertion part  24  which faces the inlet end  27  of the discharge valve  20  and an area  61  on the envelope wall  26  of the detachable inner lining  25  which is located downstream of the valve member  23 , towards the outlet end  28  of the discharge valve  20 . 
         [0045]      FIG. 4  shows the valve member  23  being in a completely closed position. In the closed position, the valve member  23  seals against the detachable inner lining  25  so that no fluid passes thorough the flow channel  22 .  FIG. 4  also shows a mating surface  50  arranged on the inner envelope wall surface  25 ′ of the detachable inner lining  25 . The mating surface  50  is sized and configured to receive the end surface  43  of the insertion part  24  of the valve member  23 , in a sealing manner in order to close the discharge valve  10 . 
         [0046]    The mating surface  50  may be formed by a recess  51  as illustrated schematically by the dashed line in  FIG. 4 . The shape of the recess  51  is adapted to receive and mate with the end surface  43  of the valve member  23 . The shape of the recess  51  is adapted to correspond to the shape of the end surface  43  of the valve member  23 . The shape of the recess  51  may be made to correspond to a circular periphery or any other suitable peripheral shape of the end surface  43  of the insert part  24  of the valve member  23 . The recess  51  and the end surface  43  of the insert part  24  may have a curvature in order to conform to the inner curvature of the detachable inner lining  25 . 
         [0047]    It should be understood that the recess  51  is an optional feature of a discharge valve  20  as disclosed herein. An adequate closure between the outer end surface  43  of the insert part  24  of the valve member  23  and the detachable inner lining  25  may be obtained without a recess  51  in the envelope wall of the detachable inner lining  25  by only providing the outer end surface  43  of the valve member with a profiled surface matching the profile of the mating surface  50  of the detachable inner lining  25 . By way of example, if the inner lining has an inner surface with a circular cross-section, the valve member may simply be provided with a correspondingly curved outer end. 
         [0048]      FIG. 5  shows a recessed mating surface  50  in greater detail. As can be gleaned from  FIG. 5 , the mating surface of the envelope wall  26  of the detachable inner lining  25  has a circular periphery with a diameter substantially corresponding to the diameter of the cylindrical body  40  so to permit the cylindrical body  40  to mate with the mating surface  50 .  FIG. 5  also shows a cut out  52  in the envelope wall  26  arranged so that the valve member  23  can properly close off the flow channel  22  of the detachable inner lining  25 . The mating surface  50  can be arranged and formed directly in the inner envelope wall surface  25 ′ if the end surface  43  of the valve member  23  is provided with a corresponding form. The recessed mating surface  50  and the cut out  52  in the envelope wall  26  as shown in  FIG. 5  are optional features of a discharge valve as disclosed herein. 
         [0049]      FIG. 6  shows a discharge valve  20  as disclosed herein with the valve member  23  in a service position. As disclosed herein, the valve member  23  may be arranged such that it can be moved completely out of the flow channel  22 , to a position in which it is clear from the detachable inner lining  25 . In the service position, the valve member  23  is moved in the displacement direction B until it is not only retracted from the flow channel  22  but moved away from the flow channel in the direction B, at least a further distance corresponding to the thickness of the envelope wall  26  of the detachable inner lining  25 . When the valve member  23  is in the fully retracted service position, where it is clear from the detachable inner lining  25 , the detachable inner lining  25  can be removed from the valve housing  21  without completely disassembling the discharge valve  20 . 
         [0050]    It should be noted that the above described discharge valve can be used with other process elements of a pulp manufacturing process and preferably mechanical pulping process but also in completely different manufacturing processes.