US2561282A - Shielding shoe for filters - Google Patents

Description

N. G. LEFFLER SHIELDING SHOE FOR FILTERS July 17, 1951 3 Sheets-Sheet 1 Filed Aug. 9, 1946 VII'IIIIIII'IIIIII 'IIIIIIIII'IIIIIIIIIIIII JVL'LV Gustav Lef/ 'ler i iTTORNEYS July N 1951 N. G. LEFFLER SHIELDING SHOE FOR FILTERS 5 SheetS -Sheet 2 Filed Aug. 9, 1946 INVENTOR WILLS Gus Zia/V Lef/ 'Ler ATTORNEYS Jufly 117, 119531 N. G. LEFF'LEFQ SHIELDING SHOE FOR FILTERS Filed. Aug. 9, 1946 zmmgz 5 Sheets-Sheet 5 INVENTOR Nils Gus td'v Lejfiler ATTORNEYfi Patented July 17, 1 951 UNITED STATES PATENT OFFICE Application August 9, 1946, Serial No. 689,314 In Sweden August 14, 1945 23 Claims. 1

The present invention relates to filters of the type embodying a movable perforated filter member adapted to pick up on its one side solids from a suspension and to discharge suspension liquid at its other side after passage through the openings thereof under the influence of a differential pressure between said sides. Such a filter is usually, but not always, formed as a rotary cylindrical drum the peripheral surface of which is perforated and provided with a fine mesh wire fabric for picking up the solids of the suspension in which the drum is partially submerged, and wherein the differential pressure is produced either by evacuating the interior of the drum or subjecting the outer surface thereof to a superatmospheric pressure. The invention is especially adapted for embodiment in rotary drum filters for picking up solids, such as fibers, powders and granules, from suspensions in liquids and is more particularly concerned with an improved construction of a shielding shoe for such filters. It is a further development of the invention I have disclosed in my previous application Ser. No. 652,464, filed March 6, 1946, for Filter.

As in the case of my previous invention above referred to, the present invention has also for its primary object to provide a shield shoe of the kind defined which will secure a sufficiently good sealing around that portion of the wire fabric where the taking off takes place. It is another object so to construct the shoe that it will in a high degree be independent of variations in said difference in pressure. A further object is to provide a sealing shoe which will close off the take off portion effectively in filter drums even if the drum is not perfectly circular. An object of the present invention in addition to the aforesaid objects is to provide a sealing shoe the frictional wear of which against the moving filter member will be immaterial.

The invention will now be described more in detail with reference to the accompanying drawings illustrating various embodiments by which the invention may be realized in connection with vacuum drums for paper making but it is to be understood that the invention is not limited to the features so shown but has to be taken in its broadest scope.

In the drawings, wherein like reference numerals indicate like parts throughout the several views, Fig. 1 is a cross sectional side elevation of the taking-off portion of a filter drum of the cell-free type and the shielding shoe according to the invention and Fig. 2 is a fragmentary front elevation of the shoe of Fig. 1 looking from the right in the latter figure, the drum being removed and a portion of the shoe being broken away to show details of construction. Fig. 3 is a fragmentary cross section of the shoe along the line 3-3 in Fig. 1. Fig. 4 is a sectional view similar to Fig. 3 showing an alternative connection between the stationary and the movable parts of the shoe. Figs. 5 to '7 show in the same way as Figs. 1 to 3, respectively, another embodiment of the invention and Fig. 8 is a fragmentary cross section showing an alternative means for securing the movable part of the shoe to the stationary part. Figs. 9 and 10 show in section and from the outer side, respectively, one embodiment, and Fig. 11 shows in section another embodiment, of certain roll supporting means according to the invention. Figs. 12 to 14 show in the same way as Figs. 1 to 3, respectively, a third embodiment of the shoe according to the invention. Fig. 15 is a fragmentary cross-sectional view similar to those of Figs. 3, 4, 7, 8, 14 and shows a flexible ribbon for securing longitudinal sealing between the stationary and the movable members of the shoe. In these views certain of the parts have been broken away or omitted, and others have been shown in full instead of in section, in order to simplify illustration of the invention.

Referring first to Figs. 1 to 3, the filter drum comprises a cylindric perforated support I on the outer surface of which the wire mesh fabric, not shown in the drawings, is applied for taking up the solids suspended in a slurry of, for instance, cellulose fibers to form therefrom the fiber cake 4. The support or filter member I is mounted in the disc-like ends 2 being rotatably journaled in bearings not shown in the drawings. At the outside of the filtering member the doctor 3 is arranged in the usual way for removing the cake 4 deposited on the filter. The drum is considered to rotate in the direction of the arrow at the upper end of Fig. 1 and to be submerged in the fiber slurry 5.

At the place of discharge of the filter, that is at the doctor knife and downwards to the level of the slurry 5, the shielding shoe is applied. The function of the shoe being to seal off the communication between the interior of the drum and the outer atmosphere, partly to facilitate the removal of the cake and partly to prevent air from getting access to the interior of the drum through the portion of the filter member made naked at the doctor, the shoe extends beyond this place of discharge at either side in the peripheral direction. The shoe is in the axial direction substantially coextensive with the filtering member or in other words with the foraminous portion thereof. In the drawings the shoe is submerged in the filtrate below the level 6 but this is not at all necessary for its satisfactory function. In filter drums where the filtrate is discharged at a low point in the drum the level of the filtrate is preferably below the lowermost portion of the shoe.

The sealing member of the shoe comprises The in-thatpart 'ofythe'foraminous portionof the";

filter member underlaicl by'the band. embodiment shown in-Figs. 1 to "3 the-:band'l is pressed against'sliding'surfaces '22 on the stationary member Hi" as well as against the filter member. lnorder to minimize the friction against the sliding-surface-E?grooves (similar to. groove 28in Fig. 3), may be made in said surface andbe connectedwiththe pressure 'medium' of the chamber through channels in'the material of the stationary member.- Once'the band has been pressed against thesliding surfaces -22 and the filter member i it will'travel with the" filter member in sealing engagement with said sliding surfaces. Means for keeping the bandinapproximate working -pos-ition---for instance a bar I or perforated pipenear the upper sliding "surface Elf-ought to be provided so that the band will be putin sealing position upon admitting pressure liquid =to the-pressure chamber, as

through said pipe.

In order, however, to insure proper function-? ing of the band in the-shoe the band'may be caused to run over guide rolls 8 and 9 and ,a jockey roll said rolls being journaled either directly in the-stationary member M or in arms In the H, 12 andi-i, respectively whicharein turn" pivoted on the-pins E15; it and H,- respectively,

secured to the" stationary member; The guide rolls 8 and 9 journaledin the arms! I and 12 r may be pressed against the filter member by means of the springs i8 and 19; The jockey" roll it is preferably pressed against the return part of the-band by means-of the "spring 20 so as to stretch the band.

To the chamber formed byjthe stationary member is and the part of the endless belt";

peripheralsurfaces 23 of thestationary member rendering said pressure chamber-- substantially liquid-tight. When using as pressure medium a; liqu'latsuch as water, an effective water lubrication of the sealing surfaces will be obtained. It isthen preferred always to keep-the band wet" on the return-run from-roll 9 to -roll 8. leakage of water into the drum-from the pressure chamber-is notharmful to the good'func Some " work 'substantiallyas described in connection 4 tioning of the filter, since the vacuum in the drum will not appreciably be influenced thereby.

Sometimes the drum can be irregular, for instance as caused by different eccentricity of the cross-sections of the drum at different places along the axis. For even in this case to secure an effective sealing a portion of the band 7 is left unsupported for some length 24 between the sealing surfaces of the stationarysmember and the filter member (as shown in'Fig. 3, the band i is unsupported at idbetween the peripheral surface 23 of the stationary member and the inner peripheral surface of the filter member I about groove .Z'l). The embodiment shown in Fig. 4 in which the sealing surface 23 of the stationary'member ill stands at a right angle to the filter'member allows a greater movement in the. radial direction of the band relative to the stationary member. In this case also the band itself is preferably provided with sealing surfaces 'atiright angles ..to, the filter member. In order. to allow theguide' rolls 8 and '9 to fol lowthe" movements required by the irregular filter member the. arms II and spin'dle'sit of the rollsi By providing the peripheral sealing surfaces '23 of the stationary member It or the impervious border of the filter membe'rrl or both with peripheral grooves 27 :and 28;respectively,fcommunicating with the. vacuum in the interior of thedrum 'byichannels, leak water. is prevented from reaching the filter cakeld'. The same efiect will be'attained'at the upperaxial sealing surface 22if the latter is provided withja similar groove.

Although 7 the pressure in the space "between the'lower sealing surface 22"and the filter member may'"be' considered'to be approximately equal to that outsidethe'filter, that is atmospheric pressure, since the filter member is here.

free from fiber cake, the pressure may, .however,

at this: place be increased byilsupplying pressure. medium from the pressure chamber or from else-- where. to this space so as to counteract a detrimental. bulging outof the band; Atthe upper sealing surface22 such an arrangement is ime practical sinceit would splash the fiber .cake-L but an .extra pressure on the outside surface of the. band is not .necessary here since the'band moves awayjrom'ithe upper. border of *the stationary.

member: whereas it moves toward thelower border.

Although not shown in the drawing the shoe may be' securedlto a stationaryshaft or to spindles in the interior-- (centre) of the drum directly or over some support devices.

supply conduit Zhfor pressure medium.=.com-

municates preferablywithlthe'. exterior .of :the.

drum through. this .shaft or spindles.

Among the advantages-of this-embodiment of "the, invention its. simple. design may. be emphasized.-

All. seals between the: band and the filter member as wellasbetween-the bandandthe-sta-v tionary member are obtainedfiwithoutextra devices. The..roll spindlesmay be journaled in "sleeves of plastics. (artificialresin) and a slight wear. of these sleeves .is insignificant.

Figs. 5 to 11 .show... another: embodiment ofthe invention. Theelements'having the. reference numerals I to 2] .Jare arranged and formedand l2 'may'lbe equipped with spherical, bearings 25 for the Bysuch means it is possible even during .operation to regulate or move'the discharge place of the.filter merely by turning said-shaftor spindleswThe 55 with the previous embodiment. The substantially liquidtight chamber is, however, here arranged within the'opening formed by the band I and is limited in the peripheral direction of the drum by the guide rolls 8 and 9. The return part of the band passes therefore outside the pressure chamber.

In the radial direction of the drum the pressure chamber is limited by the wall portion 29 of the stationary member |4. Said wall portion is sealed in the peripheral direction against the rotating guide rolls 8 and 9. The sealing can be carried out in several different ways, as by means of a ribbon of leather or rubber or similar flexible material secured (in the same manner as element 57 in Fig. 15) to the inside of the wall portion 29 so as to be pressed against the rolls by the pressure medium in the pressure chamber. In the embodiment shown in the drawing, however, the wall portion 29 is provided at the upper as well as the lower end with a groove 39 carrying the sealing bar 3|. The grooves 3|] communicate through the holes 32 with the pressure medium in the pressure chamber rendering the bars 3| resiliently pressed against the rolls 8 and 9 so that the rolls can move against and from the filter member without jeopardizing the sealing. The bars 3| may also be pressed against the rolls by springs. The seals may be located at any place on the guide rolls between the parts of the band. The lever arms H and I2 may, however, preferably be secured to the statoinary member in such manner as to limit to a minimum radial movement of the rolls 8 and 9 against the sealing bars 3| during their movement against or from the filter member.

The seal between the, pressure chamber and the interior of the drum at the tangent lines between the rolls and the band is obtained by pressing the rolls, as by springs or weights, against the inner side of the band. The movement is then limited by the filter member.

In the axial direction of the drum the pressure chamber is limited by the sidewalls 33 (Fig. '7) of the stationary member l4 and the sealing bar 34 which is resiliently movable against the filter member in sealin relation to said sidewalls 33 and the end surfaces 35 of the rolls 8 and 9. The sealing bars 34 are hinged in brackets 38 of the stationary member by means of the arms 31 pivoted to the bars by the pins 36 and to the brackets 38 by the pins 39. By this arrangement each bar is resiliently movable against the filter member. In order to secure a good sealing between the rolls 8 and 9 and the side bars 34 also in case of irregular shape of the filter member, such as may be caused by a certain eccentricity between the cross-sections of the ends of the drum, in which case the end surfaces 35 of the rolls 8 and 9 do not move in parallel to the sidewalls 33, a packing or plate 40 of elastic material, such as rubber, is provided between each of said end surfaces 35 and the cooperating sealing bar 34. For making such a movement feasible the supporting means for the rolls 8 and 9 have to be designed accordingly. In Fig. 8 one mode of carrying out such an independent movement of the ends of the roll is illustrated. In this embodiment the arms II and I2 (not shown in Fig. 8) are provided with spindles fitting in the openings of the sleeves 4| secured to the stationary shafts 42 of the rolls. In case of a relative movement of the ends of the roll in the radial direction of the drum the roll moves alittle about said spindles of the arms II and I2.

As already mentioned some leakage of water from the pressure chamber to the interior of the drum has no detrimental influence. It is therefore possible to use a labyrinth seal 43 in the rolls consistin of the grooved rotating disclike end 35 of the roll and a stationary ring 44 designed so as to cooperate with said disc-like end 35. By this means the wear at these ends 35 of the rolls 8 and 9 is avoided and the wear of the packing 40 is eliminated since the latter will seal between two elements which are stationary in relation to each other except for a slight movement to and from each other when the ends of the roll move differently in the radial direction of the drum. The packing may even be fixed to the elements 34 and 44. The elasticity of the packing will then take up the relative movement between these elements. If the roll cylinder is mounted on the stationary shaft 42 by ball or roller bearings 66 the labyrinth seal 43 may have a very small clearance. Through a sealing device 45 outside the ball bearing 66 the latter will be protected against leak water which may come into the end portion of the roll. The bearing 66 may, of course, be mounted in brackets as usual.

In the embodiment shown in Figs. 1 to 4 and in that to be described hereinbelow and shown in Figs. 12 to 15 the entire pressure difference is taken up by the stationary member 4. In the embodiment according to Figs. 5 to 7, however, a given pressure will be exerted on the guide rolls 8 and 9 which is transferred to the stationary member by the springs I8 and IS. The pressure of the springs is preferably somewhat greater than the pressure acting in the opposite direction on the rolls 8 and 9 by the pressure medium in the pressure chamber in order to bring about the sealing between the band and the roll in the peripheral direction of the drum at the side facin the filter member.

Should, however, the vacuum in the interior of the drum decrease, possibly on account of extraneous operating conditions, the roll will be pressed harder against the band. Due to the fact that the elements in question move with the same velocity and practically no frictional wear occurs, the increased pressure will not be very harmful. The variation of the pressure against the band can, however, be avoided if the guide rolls 8 and 9 are journaled in a U- shaped member or fork 46 on the pins 4! as shown in Figs. 9 and 10. The fork should be sealed against the roll. The fork is in turn pivoted on the stationary member by means of the pins 48 and arms 48'. By so locating said pins in the peripheral direction of the drum that the total effective pressures on the surfaces exposed to the pressure medium of the pressure chamber become equal on either side of the axis of the pins 48, the fork and the roll 8 or 9, respectively, journaled therein will substantially come into balance independently of the variations of the vacuum in the interior of the drum. By in-- creasing the surface of the fork exposed to the pressure chamber relative to that of the roll a constant pressure of the roll will be obtained against the band. The springs l8 and I9 may in that case be dispensed with.

Fig. 11 shows another embodiment of the pivoting of the roll in the stationary member. The sleeves 4| (Fig. 8) of the rolls 8 and 9 are journalled in the arms 49 which are in turn pivoted on the stationary member l4 on the spindles 50. The cylinder surface as well as the ends of the able in openings in thes'tationaryimember' M.

Byithi's means :the individual independent movem'entz'of thelbo'th endsuof, a rolLagainst the filter lrn'ember is 'perfect so that the roll will smoothly follow .the iirregularities of the drum.

Among thezadvantageszof the embodiment described withxreierence tosEigsvdto. 11 the very lowaveanof the (band may bementioned. This :is :dueito' the fact that thezba'nd 'does notseal "against stationarysurfaces. The. sidebars 3' 5 tare, it :is truegin the'drawing shown to be-located inrclose 'contact with the ends of .the band but for :sealing purposes1this=is not2at all v n'e'cessary, :at least not in the/v'space between the '-rolls and not-1even;at-therolls if the latter are :provided with flanges. at the ends. All sealing'elements between :movable "and stationary members: can be somewhat overdimensionedand are furthermore cheap-and can be'readily replaced.

ln liigsrm to l5 a third embodiment is shown. The elements having the reference numerals I to 2| and 29 are arranged and formed and work essentially in the same wayas'has been described in connection :with the previous embodiments with respect =-to elements having same numerals.

The substantially liqu'idtight pressure chamber lSLfllSO in this case located within the opening 'formed by the parts of the'ba'nd l. Thesealing barsi fi lat the upper and lowerendsof the wall portion 29 of thefistationarymember'are, how- -ever, contrar-y to thebarsil oi the previous embodiment, not :p-laced in contact with the rolls *6 land 9 butrthe's'hoe has instead'been designed so that=the bars 'i lsealdirectly'against the inner surface o'f-the band T'IIBELYthBFIOHS vhand 9. "By

thismea'ns sealin lagainst thecylindricsurface and-the end of 'the roll isavoided. -In order to reduce the wear of the band the sealing bars may be replaced by smalldiameter rolls rotating in contact with theband and being sealed against the stationarymember. The sealing side bars 55 limit together with the side wall 56 of the stationary member M the extension of the lplSSllIB chamber in thevaxial direction of the drum. The bars '55 are resiliently movable against the inner surface of the drum inthe sameway-as-the sealing bar34 of the preceding embodiment. JIn'Fi'g. l5 anotherembodiment of the sealing in the axial direction has been illustrated. A, flexible sealing ribbon :57 made of, for instance, leather -or rubber is here secured to the sidewall 56 i the stationary mein'ber I 4 and is :pressed against the band i or against the end 20 the filter memberzoutside the band by the-pressuremedium.

Among the advantages "of the last described embodiment the simple execution of the seals -:may be emphasized.

Since, for the contemplated function of the shoe, sealing is requiredflagainst the filter member only around the circumference of the contacting portionof the shoe, the band according to'the present invention may be replaced by one comparatively narrow belt at each .end of the rolls. The rolls should then be provided with a suitable sealing means, such as a coating or cover of rubber, betweensaid belts and in contact with the filter member; Thefsealing member being -now open towards the filter member a vapourous :pressure medium must be used in the pressure chamber formed-in the shoe. In

its inside :surfacebetween the rolls. apur-pose boxes may be used having. slots in the filter i member. rolls I disclosed may be driven by special driving means, such as chains or belts, which'm ay be order to :bring about the sealin required be'- tween the belts and the'filter'member ea'chrbelt has to be provided with a. pressing device I along For this walls facingithefbelts and inlets for a ga'seous' or liquid pressure medium to work on the belts through saidslots.

It is, of 'course,-pos'sibl'e to a'certain extent to combine the various sealing means'described in connection with the different embodiments.

At places where only minor reciprocating movements :occur the sealing elements may be nixed to the' members moving in relation to each other,

the elasticity of the' sealing means then-rendering the movement possible.

The invention hasinow been described with reference to some different embodiments but it is to be understood that 'it is -not limited to these embodiments or the special details shown and described. -In addition to various combinations of the-embodiments also quite dififer ent embodiments may comeinto question. Thustwo or more shoes of the present kind may be arranged one after the othera'nd bepr'ovid'ed with a common case "kept in liquid tight relation to the Furthermore one ormore of the driven by the shaft in the centre or thedru'm. In case the drumdsarrange'cl' 'for interior feed and the shielding shoe therefore is provided on the outer side of the drum, the driving of the-rolls can, of course, be easily performed. Employed with cell filters in which the cells -open at the one or both ends or" the drum the'shoeof-the invention will be placed over 'an appropriate number of such cell openings at the endof-endsof the drum. Although particularly described connection with filter Jdrums submerged in a suspension of fiber it is to be understood that 'theinvention can be employed equally well'i'nconjunction with other types of picking up machines for suspended solids where theseare picked upon ,a foraminous member by the action of a pressure difference-between opposite sides of the'foramin- 'ousmember.

As used in the .:speciflcation-and claims "hereof,

:the words seal and sealing are not intended to apply :solelyztoiconditions'in which a perfect zsealtis efiected, -becauseifricti'on'al sea-ls are seldom,

ever, absoiutely air-tight or watertight. In-

stead, these Words should be interpreted to mean :that the leakage of air, water or other fluid is inhibited to the maximum degree practicable in structures of the character described, and that where the seal is made by frictional engage- -ment. between relatively movable members, a

limited amount of leakage may exist without seriously impairing the utility of the invention.

Vilhat is claime'dds:

A sliie'lding shoe for filters of the type embodyinga movable perforated filter member adapted to pick up o'h "its one side solids from a suspensionandto d'ischar-ge suspension liquid at its other side after passage through the openings thereof under the iniluenceof a difierential pressure between said sides, said shoe comprising supporting said endless-flexible -member for movement relative to said stationary shoe member and with said perforated filter member, said stationary shoe member including walls forming a chamber having an open side facing said perforated filter member, means including said endless flexible member for closing the open side of said chamber and rendering the latter substantially liquidtight, and mean for supplying fluid under pressure to said chamber for pressing said endless flexible member into contact with said perforated member.

2. A shielding shoe as claimed in claim 1 wherein at least one end of said stationary shoe member is provided with a supporting surface over which said endless member passes in sliding engagement, and which includes means for maintaining said endless member in approximate working position adjacent said surface.

3. A shielding shoe as claimed in claim 2 including grooves in said supporting surface communicating with said chamber. 4. A shielding shoe as claimed in claim 1 including at least one roll about which said endless member is movable, said roll being disposed adjacent the rear end of said stationary shoe member as viewed in the direction of movement of said endless member.

5. A shielding shoe for filters of the type embodying a movable perforated filter member adapted to pick up on its one side solids from a suspension and to discharge suspension liquid at its other side after passage through the openings thereof under the influence of a differential pressure between said sides, said shoe comprising a rigid stationary shoe member and a movable sealing shoe member, said movable sealing shoe member comprising two rolls disposed one at each end of said stationary shoe member and an endless flexible band of impervious material movable about said two rolls and adapted to contact and seal a portion of said perforated filter member and to move revolvingly therewith, means for rotatably supporting said rolls from said stationary shoe member, said means being so constructed and arranged that at least one of said rolls is movable relatively to said stationary shoe member toward and away from said perforated filter member, said stationary shoe member including walls forming a chamber having an open side facing said perforated filter member, means including said endless flexible band for closing the open side of said chamber and rendering the latter substantially liquidtight, and means for supplying fluid under pressure to said chamber for pressing said endless flexible band into contact with said perforated filter member.

6. A shielding shoe as claimed in claim 5 wherein said roll supporting means includes an arm pivotally mounted on said stationary shoe member, and. means for rotatably journalling said movable roll in said arm.

'7. A shielding shoe as claimed in claim 5 including at least one additional roll in contact with said endless band, adjustable means for rotatably supporting said roll from said stationary shoe member, and yieldable means for urging said roll in such direction as to stretch said band.

8. A shielding shoe for filters of the type embodying a movable perforated filter member adapted to pick up on its one side solids from a suspension and to discharge suspension liquid at its other side after passage through the openings thereof under the influence of a differential pressure between said sides, said shoe comprising a rigid stationary shoe member, and a sealing shoe member at least a part of which is movable relative to said stationary shoe member, said sealing shoe member comprising a pair of rolls, one at each end of said stationary member, and an endless flexible member of impervious material movable about said rolls, said endless member having a contacting portion movable along with and, at least for the greater portion of its length, in contact with said movable filter member and a return portion, said stationary shoe member including walls forming a chamber having an open side facing said movable filter member, and means including the contacting portion of said endless member for closing the open side of said chamber and rendering the latter substantially liquidtight.

9. A shielding shoe as claimed in claim 8 wherein the return portion of said endless flexible member is within said chamber.

10. A shielding shoe for filters of the type embodying a movable perforated filter member adapted to pick up on its one side solids from a suspension and to discharge suspension liquid at its other side after passage through the openings thereof under the influence of a differential pressure between said sides, said shoe comprising a rigid stationary shoe member, a pair of rolls substantially parallel to one another, and an endless flexible member of impervious material movable about said rolls, said stationary shoe member including a wall portion spaced from and generally parallel to said movable filter member, located between said rolls and in substantially liquidtight contact therewith, said endless member having a portion between said rolls generally parallel to said wall portion movable along with and, at least for the greater portion of its length, in contact with said movable filter element, and means including, said wall portion of the stationary shoe member, said rolls and the filter contacting portion of said endless member forming the enclosure of a substantially liquidtight chamber.

11. A sealing shoe as claimed in claim 10 including a pair of sealing bars extending between said rolls at the ends thereof and yieldably movable toward said movable filter member, said sealing bars having substantially liquidtight contact with said rolls and said stationary shoe member.

12. A shielding shoe for filters of the type embodying a movable perforated filter member adapted to pick up on its one side solids from a suspension and to discharge suspension liquid at its other side after passage through the openings thereof under the influence of a differential pressure between said sides, said shoe comprising a rigid stationary shoe member, an endless flexible member of impervious material revolvingly movable relative to said stationary shoe member and having a portion spaced from said stationary shoe member and adapted to contact.

a portion of said movable filter member, sealing means between said stationary shoe member and the inside surface of said endless member at the ends of said stationary shoe member in the direc-' tion of movement of said endless member, means including said stationary shoe member and the portion of said endless member between said sealing means forming the enclosure of a substantially liquidtight chamber, and a conduit leading to said chamber.

13. A shielding shoe as claimed in claim 1 including at least one roll rotatably supported by said stationary shoe member and about which 2&5 6 13282;

said-endlessflexible member-is movable, the-ends.- ofjsaid'lroll being. independently: movable toward and away from said filter member.

14-.-..A shielding shoe.= for filters of the type embodying a filter-member comprising. aspere forated portion surrounded by an imperviousframeportion and being adaptedto pick p on its--one side: solids froma suspensionand to dis-. charge suspension liquid at its other sideafter passage through the openings thereof under the influence-of a diiferential pressure between. said sides, said shoe comprising-a rigid stationary shoe member having a sidewall generally parallel to said filter member, end:- wallsperpendicularto said-sidewall and an open side-facing saidrfilter member, an endless band of impervious material movable relative to said stationary shoe member. and closing theside thereof facing. said. filter member exceptrfor relatively narrow spacesbetweenthe end walls of said stationary shoe member and the edges of said-endless band, pertions-of said endlessband adjacent its edges-being. in contact with the impervious frame portionof. saidfilter member, and means'forsealing said spaces, said sealing-means.being:-. so constructed andarranged as to maintain-the seal While per.--

member, into frictional engagement: with said.-

impervious-frame portion.

16. A shielding-shoe as: claimed. in claim. 15. wherein-saidisealingbar is provided with-asun-v face perpendicular to saidband'and in sliding engagement with the'edge thereof i 17.'A shielding shoe. asclaimed inclaim 14.

wherein a said sealing, means comprises va. flexible sealing ribbon fixed to eachv end wall, of said, stationary= shoe member and so constructed and. arranged that one of its surfacesis-inicontact.

with r the; portion: of said endless band. adjacent said endwalli.

18..-.A sealing shoe as claimed. inv claimkl.

wherein said sealing means comprisesasurface on said stationary shoe memberparallel to and ill-Sliding contactwithithe marginalportion of. said band, said band having an unsupported pore tion between :the portions thereof in contact with saidrimpervious frame portion andsaid surface.

19, A shielding shoe as claimed inclaim 18. wherein atleast one of theportions. of saidime pervious frame. portion and said surface in contact with-said endless band is provided witha.

groove communicating with asourceofvacuump 20. A shielding shoe for filters of the. type em-:- bodying a movable perforated filter member.

adapted topick up. on itsonesidesolids from. a suspension and to, discharge suspensionliquid.

1'2 less member having; :a-contaeting portion movable along: with and, at lleastfor the. greatest portion' of-its? length; in contact: with said movablefilter member and a return portion; said stationary shoe'memberincluding wallsv forminga-chamber havingian, open side facing said movablefilter member, means including the portionof said endless member inpcontactwith said movable-filter member for closing-theopen side ofsaidchamber and rendering the latter: sub stantially liquidtight, means fonsupplying a fluid underpressure to said .-chamb'er,qand means outside saidc-hamber for supplying liquid under-pres sure-to the coil-tasting portion of; said endless:

member.

21. A shielding. shoe as claimed in' claim 1' includingat least one feeder; roll about which said endless flexible member.- is; movable.-

22.- A shielding shoe as claimed in claim: 1

including-a flexible sealing ribbon fixed to saidstationary shoe member and so-constructed and arranged: that one. of 1 its .sides :ismaintained in sealing contact with said endless-flexible member byr'the pressure in saidchamber.

23. A shieldingshoe for filters of the: type embodymg afilter member comprising i a perforated portion surrounded by an impervious .frameipoz tionv and being adapted to pickup on it'sone side solids; from a; suspension and to discharge suspension liquid at itsother side after passage through theopenings thereof under theinfiuence' of ardifierential pressure between said sides, said shoe comprising a rigid stationary shoe memberhaving a, side: wall generally parallel :to said-- filter member and end walls perpendicular-tosaid side' Wall forming-'a chamber having an openside fac-' ing saidfiltermemher, an-rendless band of impervious: materialmov-able'relative to said stationary. shoemember and having portions adj acent. its; edges in contact with theimpervious frame portion of said filter member; saidbandand: imperviousframe portion closing the openside-of. said chamberexcept' for relatively marrow spaces between theend walls of said' sta-l tionary shoe-member and said impervious frame portion, and-means for'sealing said-spaces-to rendersaidchamber substantially liquidtight;

said meanso-being so-constructed and-arrangedas to. maintain the seal= while permitting rotary movement-of said impervious=f-rame portion relative to saidstationary shoe member.

N ILS-GUSTAV LEFFLER;

REFERENCES CITED The-following references are ofrecord' in the file of this-patent:

UNITED STATES PATENTS

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