WO2002002204A1

WO2002002204A1 - Sealing arrangement

Info

Publication number: WO2002002204A1
Application number: PCT/FI2001/000610
Authority: WO
Inventors: Anssi Luostarinen; Pekka Purho; Erkki Ruuskanen; Petri Tarjavuori; Paavo Tolonen; Juha Vellonen
Original assignee: Andritz-Ahlstrom Oy
Priority date: 2000-07-04
Filing date: 2001-06-27
Publication date: 2002-01-10
Also published as: AU2001272594A1; FI20001603A; FI20001603A0

Abstract

The present invention relates to a sealing arrangement for sealing the end of a rotating cylindrical member, such as a shaft or a drum, in the filters or washers of the wood processing industry in relation to the outer shell or other component of the filter or washer surrounding said member. The sealing comprises a stationary ring-shaped plate (141) located essentially concentrically with said cylindrical member (118) in a distance from the end surface of (119) of the cylindrical member, in which ring-shaped plate there are preferably fitted at least two sealing rings (143' and 143'') having different diameters and a propelling member (153) corresponding to each ring. A pressure medium flow is directed to the propelling member so that by means of said propelling member the sealing rings (143' and 143'') are protruded outwards from the stationary ring-shaped plate in the axial direction and pressed against the plane end surface of the rotating cylindrical member (119) for effecting the sealing.

Description

Sealing arrangement

The present invention relates to a sealing arrangement for sealing the end of a rotating cylindrical member, such as a shaft or a drum, in the filters or washers or the like appa- ratuses of the wood processing industry in relation to the outer shell or other component of the filter or washer surrounding said member. This kind of filters may be utilized e.g. in causticizing processes for separating white liquor and lime mud.

In the processes of the wood processing industry, conventional apparatus comprise drum or disc filters and drum or disc washers. One such device is a pressurized disc filter presented in Fig. 1 or US-patent 4,929,355, which filter is used e.g. in separating white liquor and lime mud or in filtering green liquor. This kind of pressurized disc filter comprises a pressure-proof essentially cylindrical shell positioned horizontally so that a horizontal shaft may be arranged supported by the closed pressure ends of the cylinder. Discs, preferably formed of sectors, are arranged on the shaft with a spacing from each other, as in known from various publications describing disc filters, e.g. US-patent 3,948,779. Further, as know from prior art, said shaft is preferably provided with as many channels in the axial direction as there are sectors in the discs, as also disclosed in the latter US-patent. The purpose of said channels is to lead the filtrate, which has passed into the discs through their perforated surface, covered by a filter cloth, out of the device via a filtrate valve/filtrate valves arranged either at one end of the shaft or both ends of the shaft. Additionally, in the lower part of the device, on the descending side of the discs and on both sides of the discs there are chutes arranged extending in most cases approximately to the height of the shaft of the filtering device, into which chutes the material deposited on the discs is removed by appropriate means and which chutes lead the deposited material out of the device. This has been described earlier, e.g. in said US patent 4,929,355. Said removal means may comprise various mechanical scrapers or liquid or gas sprays, by means of which the deposited material is removed from the perforated surface of the discs/sectors. This removal is often assisted by arranging a pres- surized air blow via the discs, the channels of the shaft and the filtrate valve for blowing off material from each sector surface when it reaches the blow zone. The filtrate valve mentioned above is a significant component in view of the operation of said device, hi the filtrate valve, multiple filtrate flows from the rotating shaft of the filtering device are combined to form one filtrate discharge flow passing via a single stationary discharge pipe. Further, by means of the filtrate valve the blow for releasing material is directed via the filtrate channel on the shaft to filter sectors from which material is being removed. One of the problems in this prior art solution has been e.g. the non-rotating wear plate of the filtrate valve, which plate has had ports with the same spacing and radial distance from the center line of the shaft as there are filtrate channels on the shaft and which is tightly pressed on the wear plate arranged at the end of the shaft. Said problem is further complicated by the fact that, as seen in fig. 1, the internal pressure of the pressure shell of the device can extend its effect to almost the whole surface area of the filtrate valve, pressing the valve towards the end of the shaft, whereby the sliding surfaces of the wear plates are subjected to a significant pressure load.

A specific lubrication system has been developed for said construction, by means of which system lubricant, preferably grease, is guided between the wear plate of the end of the shaft and the wear plate of the filtrate valve for increasing the lifetime of the sliding surfaces and ensuring the sealing. The lubrication system requires a separate device, which forms an additional object of maintenance, hi case of system failure or lubricant run-out due to neglected maintenance the wear plate will wear out faster. The replacement interval of the wear plate is decreased. The replacing of the wear plate is a demanding task, because said wear plate is located inside the pressure shell of the filtering device and, furthermore, behind the whole filtrate valve. Thus, in order to replace the wear plate, all liquid and other conduits at the end of the shaft have to be dismantled, the service access of the filtrate device at the end of the shaft has to be opened and the whole filtrate valve removed before it is possible to change the wear plate. Additionally, proactive maintenance is not possible, as it is not possible to check the condition of components demanding maintenance without dismantling the filtrate valve. The object of the present invention is to eliminate said problems and to provide for a new kind of construction for sealing the shaft and other corresponding rotating cylindrical members in the filters and washers of the wood processing industry. Especially the object is to provide for a sealing construction having a longer lifetime than prior art so- lutions, being easier to maintain and having a higher sealing reliability.

A characteristic feature of the sealing arrangement according to the present invention is that the sealing comprises a stationary ring-shaped plate located essentially concentrically with said cylindrical member in a distance from the end surface of the cylindrical member, which ring-shaped plate is provided with one sealing ring or at least two sealing rings having different diameters and a propelling member corresponding to each ring and that the stationary ring-shaped plate is provided with means for leading a pressure medium into said stationary ring-shaped plate and for directing the pressure medium flow to the propelling member so that by means of the propelling members the sealing rings are pushed in the axial direction outwards from the stationary ring-shaped plate and pressed onto the end surface of the rotating cylindrical member for effecting the sealing.

Especially preferably the propelling member is a solid O-ring, which as a propelling member has many preferable advantages. An O-ring does not burst and it is firm. The propellant air connection is simple and secure. When utilizing an O-ring, there are no such restrictions to the axial movement of the propelling member, which the extensibility of rubber sets when using tubular material.

Preferably there are at least two sealing rings, hi such a case water may be directed between the sealing rings. The water flows partially between the surfaces sliding against each other. Heat being generated by the friction is transferred away with the water.

The present invention relates also to a filtrate valve construction applying the sealing arrangement according to the present invention. Other characteristic features of the present invention are disclosed in the appended claims.

The stationary ring-shaped plate (sealing body) is located in a distance from the plane end surface of a rotating cylindrical member, whereby the distance is such that the rotating end surface and the stationary ring-shaped plate essentially do not touch each other. The stationary ring-shaped plate is located essentially concentrically with said cylindrical member. Essentially concentrically covers also possible minor radial motion of the rotating cylindrical member, such as a shaft, during the operation of the device.

The invention is disclosed in more detail in connection with the utilization of the sealing according to the present invention in a pressurized disc filter, but the sealing according to this invention may be utilized also in connection with a drum filter as well as drum and disc washers, various thickeners and roller presses.

The present sealing is especially preferred in a filter, in which the filter valve wherethrough the filtrate is led from the internal space of the shaft to the outside of the filter, has a new kind of construction. The filtrate valve may be positioned on the outer surface of the pressurized filter shell so that the maintenance of the filtrate valve may be per- formed from outside the pressurized shell. Alternatively the filtrate valve may be formed by arranging a conical casing inside the pressurized filter shell, between the end of the shaft and the end of the shell. The conical casing isolates the inner space of the filtrate valve from the pressurized inner space of the filter.

Advantages of the sealing according to the invention are e.g. the following

- the sealing forms according to the surface to be sealed

- the sealing allows radial and axial movements of the rotating member

- the friction coefficient with respect to the surface to be sealed is small

- the construction is simple - the deformation or thermal expansion of the parts does not affect the sealing force or the operation of the sealing. The invention is described in more detail with reference to the appended figures, of which

Fig. 1 illustrates a prior art pressurized disc filter, Fig. 2 illustrates a sealing according to the invention in connection with a filtrate valve construction,

Fig. 3 illustrates a sealing construction according to a preferred embodiment of the invention,

Fig. 4 illustrates a prior art sealing in connection with another filtrate valve construction, and

Fig. 5 illustrates the use of a sealing according to the invention in a pulp washer.

The prior art pressurized disc filter 10 illustrated in Fig. 1 comprises a pressure-proof essentially cylindrical shell 12 located horizontally so that a horizontal shaft 18 may be arranged between the closed pressurized ends 14 and 16 of the cylinder. Discs 20, preferably formed of sectors, are mounted on said shaft 18 in a distance from each other, as known from various publications describing disc filters. Further, according to prior art, said shaft is provided with channels 22 preferably in the axial direction, the number of which channels equals the number of sectors in the disc 20. The purpose of said chan- nels 22 is to lead from the discs 20 the filtrate passed into the internal space of the discs 20 through their perforated surface out of the device 10 via filtrate valve 24 arranged at the end of the shaft 18. Additionally, at the bottom part of the device, on the descending side of the discs 20, there are chutes 26 arranged extending most usually approximately to the height of the shaft 18 of the filtering device, to which chutes the material depos- ited on the discs 20 is removed from the discs by appropriate means 28 and which chutes 26 lead the deposited material out of the device 10. Said removing means 28 may comprise various mechanical scrapers or liquid or gas sprays, by means of which the deposited material is scraped off the perforated surface of the discs/sectors 20. This removal is often assisted by means of pressurized air blow via the discs 20, the channels 22 in the shaft 18 and the filtrate valve 24, for blowing off material from each sector surface in the blow zone. hi a pressurized filter the filtering is often intensified by arranging both positive pressure inside the shell of the filtering device and suction inside the filter discs. For the construction described in the above, this has the disadvantage that the filtrate valve 24 is totally located inside the pressure shell, whereby practically all measures connected with the maintenance inevitably require opening the pressure shell and taking all measures in connection therewith, hi the illustration of Fig. 1 it is also seen, how the internal pressure of the pressure shell of the filtering device may affect the surface of the filtrate valve on the right hand side of the valve to a remarkably greater extent than on the left hand surface of the valve. This leads to a great loading caused by pressure on the wearing surfaces between the non-rotating valve 24 and the rotating shaft 18.

The filtrate valve 24 comprises a body 30 located inside the pressure shell of the filtering device and is supported by adjusting rods 32 onto a flange 34 at the end of the filtering device, which flange forms part of the pressure shell of the filtering device, hi the center of the body 30 of the filtering device 24 there is arranged an opening for the shaft of the discs so that the bearing application of the shaft may be arranged e.g. in connection with the flange 34 at the end. The body 30 is further provided with a wear plate 36 located against the corresponding wear plate 38 arranged at the end of the shaft 18 of the filtering device. By means of the adjustment rods 32 and springs preferably arranged in connection therewith, the force pressing the wear plates together may be regulated. The main purpose of the wear plates 36 and 38 is to form a sealing between the rotating shaft 18 and the body 30 of the non-rotating filtrate valve 24. hi practice, by means of said wear plates a sealing is formed which keeps the pressurized space of the filtering device and the subatmospheric pressure space inside the filtrate valve apart, thus ensuring the operation of the device. In one construction the wear plate located on the side of the shaft and rotating together with the shaft is provided with a port for each filtrate channel of the shaft. The only essential feature of the wear plate 38, though, is that it keeps the filtrate channels bringing in filtrates apart from the filtrate channel, wherethrough pres- surized air is blown inside the discs for releasing material from the perforated surface of a certain sector/s of the discs. Just accordingly, the wear plate 36 may be provided with ports for each filtrate channel, but most usually the wear plate 36 comprises kind of two circles having different diameters, which circles are connected by a sealing sector surrounding the blow opening and additionally by a few essentially radial bridges arranged only for strengthening the construction.

hi the construction illustrated in the figure, the body 30 of the filtrate valve 24 further comprises a conduit 40, wherethrough the filtrate is led out of the filtrate valve 24 and the filter 10 itself. The filtrate valve 24 is further provided with a second conduit 42, wherethrough material is blown off from the surface of the filtering disc 20.

Figure 1 illustrates also how the shaft 18 of the filtering device extends, with a smaller diameter, through the body of the filtrate valve essentially up to the flange 34. hi the construction according to the figure, there is a conical casing 44 attached on the flange 34, which casing extends to the vicinity of the shaft and covers inside it both the actual mechanical sealing and the bearing assembly of the shaft in relation to the flange 34.

It is seen from Fig. 1 that all constructions on the right hand side of the filtrate valve, such as adjustment rods, 32, the bearing assemblies of the shaft and the sealings thereof, remain exposed to the effect of the material being treated, hi practice this means that lime mud or some other material being filtered is accumulated in layers e.g. on the adjustment rods 32 hindering the operation of the rods 32.

It has to stated about the construction illustrated in the figure that all conduits, adjustment rods and the like leading through the flange are located in a pressurized space, which requires especially thorough sealing of their inlets in the flange and thus leads to expensive and in many cases also excessively complicated constructions. That is the case especially if the material to be treated is some hot and/or corrosive chemical.

Figure 2 illustrates a sealing according to a preferred embodiment of the invention and a new kind of filtrate valve 124, in connection wherewith the use of the sealing is pre- ferred. Said filtrate valve is meant to be used in new filters or filters that may be modernized with slightly greater investments.

The body 130 of the filtrate valve is fixed to the end of the pressure shell of the filtering device with a flange 126. The body of the filtrate valve is cylindrical, although it may also be polygonal or conical. The filtrate channels in the shaft 118 open directly into the internal space 146 of the filtrate valve 124 without any filtrate valve or the like comprising a pair of wear plates at the end of the shaft. From space 146, the filtrate is led out via a filtrate conduit 144. Reference numeral 134 shows the location of the bearing as- sembly of the shaft 118, although the details are not shown.

The filtrate valve 124 is located essentially completely outside the end wall of the device. In other words, unlike the solution of figure 1 where the filtrate valve is located in a pressurized space inside the pressure shell of the device, the filtrate valve according to the invention is located in connection with the pressure shell, whereby the maintenance of the filtrate valve may be performed from outside the pressure shell. The condition of the internal space of the filtrate valve and its parts may be monitored via an inspection glass 147.

Figure 2 illustrates further that the apparatus for removing filtered material or precoat- layer, i.e. the blow-off apparatus, comprises a blow conduit 150. In this embodiment, there is a flange 152 fixed on the end flange 132 or end plate of the filtrate valve, to which flange 152 in turn there is fixed a small-sized actuating cylinder 154, inside of which there is a pipe 156 wherethrough the air blow is directed under the filtering sur- face. At the end of the pipe 156 there is arranged a sealing ring (pipe seal) 158, by means of which the connection between the conduit 150 and the filtrate channel of the shaft 118 being in the blow phase and opening to the face surface 157 is sealed to be essentially air proof.

The shaft 118 is sealed in relation to the pressure shell 116 of the filter surrounding it or more precisely to the flange 126 fixed onto the filter shell by means of an axial sealing 140 according to the invention, whereby the internal space 146 of the filtrate valve is isolated from the pressurized internal space of the filtering device, hi other words, essentially the same pressure is prevailing in the internal space 142 of the filtrate valve as in the filtrate channels of the shaft or further underneath the filtering surfaces.

The new axial sealing 140 comprises a stationary ring-shaped plate 141 fixed onto the end or the flange 126 of the filtering device by means of mechanical fasteners 142, such as bolts. Respectively, on the face surface of the shaft 118 there is arranged a wear plate 119 which seals the joint of each filtrate channel in the blow phase and the blow conduit 150 and also seals the internal space 146 of the filtrate valve in relation to the internal space of the filtering device with the new sealing 140. The stationary ring-shaped plate

141 is located in a distance from the wear plate 119, the distance being such that the rotating wear plate 119 and the stationary ring-shaped plate 141 essentially do not touch each other. Inside the stationary plate 141 there are imbedded essentially concentrically with the center point of the stationary plate two sealing rings 143' and 143" having different diameters. The material of the sealing rings is wear resistant material having low friction, such as e.g. carbon teflon.

The sealing 140 is illustrated in more detail in figures 3A - 3D. Figure 3D illustrates a stationary ring-shaped plate 141, which is fixed to a flange 126 by means of fasteners 142. The plate 141 is provided with grooves 148 and 149, into which the sealing rings 143' and 143" are adapted. The sealing is effected by pressing the sealing rings by means of a pressure medium, such as pressurized air, against the wear plate 119 at the end of the shaft. At the bottom of the grooves 148 and 149 there are solid O-rings 153 (fig. 3B), behind which pressurized air is led via conduit 145 (fig. 3 A), whereby the O- ring presses the sealing ring located in the same groove against the wear plate 119 of the shaft for effecting sealing between the shaft 118 and the flange 126 surrounding it, which flange 126 is arranged to the filter shell.

Fig. 3B illustrates how the sealing rings 143' and 143" are locked into the stationary plate (sealing body) 141 by attaching means 155 so that they will not start rotating to- gether with the shaft 118, but move in the axial direction. Additionally, sealing water may preferably be introduced between the sealing rings 143' and 143" via conduit 159. The water flows between the sealing rings and partially also between the surfaces sliding against each other and it is removed via conduit 160. Thereby the heat caused by friction is transferred away with the water.

Even though the construction of this embodiment to some extent resembles the prior art solution presented in the above in Fig. 1, there is the distinct difference that in the prior art solution the filtrate valve did not in any way communicate with the outer shell of the filtering device, but was located completely in the pressurized internal space of the filtering device. This resulted in earlier described disadvantages, which have been eliminated by the solution according to the invention by arranging the filtrate valve to be partially defined by the outer shell of the filtering device or even to form a part thereof. The filtrate valve construction presented in Figure 2 may also be applied in modernization of older filters. In such a case, both the filtrate valve and the shaft of the filtering device have to be replaced, because in the older construction the filtrate channels in the shaft of the filtering device open to the end of the shaft far inside the filtering device. It is possible to arrange one or more additional filter discs on the new shaft of the filtering device, whereby the capacity of the filtering device may be remarkably increased.

Figure 4 illustrates a solution according to a second preferred embodiment of the invention, which solution makes it possible to replace the prior art filtrate valves presented in Figure 1 with a new kind of filtrate valve. It is a so-called direct retrofit solution, according to which the filtrate valve that used to require often laborious maintenance has been replaced with a solution having longer maintenance intervals and being essentially more service-friendly than earlier solutions. Figure 4 illustrates parts and components introduced already in connection with Figure 1 by the same reference number, but replacing the first digit "1" in the reference numbers of Figures 3 A - 3D by digit "2", respectively. The solution of Figure 4 is based on separating the filtrate valve or, in this construction actually the end of the shaft 218 from the rest of the internal space of the filtering device by arranging according to the figure a conical casing 264 between the shaft 218 and the flange 226 fixed onto the end 216 of the filtering device. In sealing said stationary casing 264 in relation to the rotating shaft 218, the axial sealing 240 according to the invention may be applied, the purpose of which sealing is to maintain the pressure differ- ence between the internal space of the filtering device and the internal space 246 of the filtrate valve and naturally also to prevent the material being filtered from entering the internal space 246 of the filtrate valve.

The stationary ring-shaped plate 241 of the sealing according to the invention is fixed by means of mechanical fasteners 242 onto the conical casing 264. Under the effect of the pressure medium, the sealing rings 243' and 243" are pushed against the wear plate 219 arranged at the end of the shaft to effect the sealing. Sealing water is led between the sealing surfaces via conduit 259 and discharged via conduit 260.

As seen from the above, the invention provides for a very reliable and dependable filtrate valve construction. The reliability is very much based on minimizing the size and number of wearing parts in the device, as well as the time they are exposed to wearing. As already mentioned, the method and apparatus according to the invention may be utilized in connection with both disc and drum filters. Further, said devices may be ei- ther pressurized or under atmospheric pressure. And still further, the materials to be treated may comprise either fiber suspensions, various liquors, lime mud of the wood processing industry or some other liquid or suspension requiring filtering.

By means of the construction according to a preferred embodiment of the present inven- tion the filtrate valve is arranged apart from the pressurized space of the filtering device so that the condition of the filtrate valve may be monitored during the operation of the filtering device. At the same time said solution also makes it possible to essentially simplify the construction of the filtrate valve compared to prior art filters.

The device according to the present invention contributes to facilitating the maintenance, as the filtrate valve is connected to the pressure shell of the device. This new so- lution makes it possible to arrange the filtrate valve on the outer surface of the shell, whereby the monitoring and maintenance may be carried out via inspection glasses and maintenance holes located on the outer surface of the shell, hi the new solution the sealing between the shaft and the filtrate valve may be serviced from outside the filter without dismantling the shaft and the bearing assemblies.

Figure 5 illustrates the use of the sealing according to the invention for sealing the end of the drum of a pulp washer in a pulp mill. The figure is a cross-sectional partial view of an end of a so-called DRUMDISPLACER^® washer. This kind of washer has been presented in e.g. US patents 5,120,398 and 5,139,671. The washer in question comprises, as far as the components visible in the figure are concerned, a stationary outer shell 312, a washing liquid feed chamber 314 disposed inside the housing, an end flange 316 of the chamber and a stationary substantially cylindrical perforated plate 320 defining the feed chamber wall by the shaft. The washer further comprises a washing drum located in a distance inside said perforated plate 320, which drum has a diameter of about 3 to 5 meters and a length of 3 to 10 meters and a surface formed of an essentially cylindrical perforated plate 318. Between the perforated plate 320 defining the washing liquid feed chamber 314 and the perforated plate 318 of the drum there is a space 322, into which the fiber pulp suspension to be washed is fed. In the direction of the end of the drum said space is defined by an end plate 324 of the drum. Inside the perforated plate 320 of the drum there is a so-called filtrate chamber 326, which is defined on the side of the shaft by a non-perforated inner shell 328 of the washing drum. From the filtrate chamber 326, the filtrate is led via an opening 330 in the end plate of the drum and a filtrate channel 336 in the sealing body 341 to collection chutes 334 for filtrate.

The sealing according to the present invention may be utilized e.g. for isolating a fiber pulp space 322 of a rotating washing drum from the outside of the washer, washing liquid feed chambers 314 from the filtrate channel 336 and the filtrate channel 336 from ambient air. The stationary ring-shaped plate 341 acting as the sealing body is fixed with mechanical fasteners, such as bolts 342, onto the stationary end plate 316 of the feeding chamber in a distance from the end surface 324 of the rotating drum. The stationary ring-shaped plate 341 has two pairs of grooves 346 and 347, 348 and 349 located on different sides of an opening 330 for filtrate in the end cylinder of the drum, which opemng 330 extends in the ring-shaped plate in form of chamber 336. Each groove is provided with a plane sealing ring 343 and an O-ring 344, behind which a pressure medium, such as pressurized air is led for pushing the sealing rings from the stationary plate 341 against the end cylinder 324 of washing drum in order to effect sealing between the end of the rotating drum and the stationary part of the washer surrounding it. Water may be led between the sealing surfaces for cooling and lubricating the sealing, as described in connection with the figures in the above.

Claims

1. Sealing arrangement for sealing the end of a rotating cylindrical member, such as a shaft or a drum in filters, washers, thickeners or the like devices of the wood processing industry in relation to the outer shell or some other part of a filter, washer or thickener surrounding said member, characterized in that the sealing comprises a stationary ring- shaped plate (141, 241, 341) located essentially concentrically with said cylindrical member (118, 218, 318) in a distance from the end surface (119, 219, 324) of the cylindrical member and having one sealing ring or at least two sealing rings (143' and 143", 243' and 243"; 343) sealing rings with different diameters and a propelling member (153, 344) corresponding to each ring, and that the stationary ring-shaped plate is provided with means (145) for leading a pressure medium into the stationary ring-shaped plate (141, 241, 341) and directing the pressure medium flow to the propelling member so that the sealing rings (143' and 143", 243' and 243"; 343) are pushed by means of the propelling members outwards from the stationary ring-shaped plate in the axial direction and pressed against the plane end surface (119, 219, 324) of the rotating cylindrical member for effecting the sealing.

2. Sealing arrangement according to claim 1, characterized in that the propelling member is an O-ring.

3. Sealing arrangement according to claim 2, characterized in that the stationary ring-shaped plate (141, 241, 341) is provided with grooves (148, 149) wherein the sealing rings and propelling members are fitted.

4. Sealing arrangement according to claim 1, characterized in that there are two sealing rings and that the sealing comprises means for leading sealing water to flow between the sealing rings.

5. Sealing arrangement according to claim 4, characterized in that the stationary- ring-shaped plate has means (155) for fixing the sealing rings to said stationary ring- shaped plate for preventing the rings from rotating but allowing axial motion.

6. Sealing arrangement according to any of the preceding claims, characterized in that the rotating cylindrical member is a shaft (118, 218) in some filter of a causticizing plant in a pulp mill.

7. Sealing arrangement according to any of the preceding claims, characterized in that the rotating cylindrical member is a pulp washer drum (318) of a pulp mill.

8. Filtrate valve for leading filtrate from the filtering surfaces of a filtering device, such as a disc or drum filter, to the outside of the device, which filtrate valve (124, 224) comprises means for leading filtrate from the filtrate channels of the filtering device to means (144, 244) for receiving the filtrate, characterized in that the valve further comprises means for isolating the internal space (146, 246) of the filtrate valve from the internal space of the filtering device and that said means comprise a sealing arranged between a rotating shaft (118, 218) and a stationary end flange (126, 226) of the filtering device or a member (264) attached to said end flange, which sealing comprises a sta- tionary ring-shaped plate (141, 241) disposed substantially concentrically with the shaft (118, 218) in a distance from the end surface (119, 219) of the shaft and having fitted therein one sealing ring or at least two sealing rings (143' and 143", 243' and 243") with different diameters and a propelling member (153) corresponding to each ring, and that the stationary ring-shaped plate is provided with means (145) for leading a pressure medium into said stationary ring-shaped plate (141, 241) and directing the pressure medium flow to the propelling member so that by means of the propelling member the sealing rings (143' and 143", 243' and 243") are pushed in the axial direction outwards from the stationary ring-shaped plate and pushed against the plane end surface (119, 219) of the rotating cylindrical member for effecting the sealing.

9. Naive according to claim 8, characterized in that said member is a body (264) extending from the end of the filtering device towards the inside of the filtering device, the end of which body inside the filtering device being provided with said sealing, said body forming part of the outer surface of the filtrate valve relative to the internal space of the filtering device.

10. Naive according to claim 8, characterized in that said member is a cylindrical body (130) which is attached to the end of the filtering device on the outer surface (116, 126) of the shell, the sealing of which body being arranged at the end of the body at- tached to the surface of the shell of said filtering device.

11. Naive according to claim 8, characterized in that the propelling member is an