the filtering apparatus according to fig1 has an exterior housing 10 , which consists of a cap - shaped air inlet component 11 and a kettle - shaped main housing component 12 containing an air outlet 36 . the main housing component 12 contains a fiber filtering assembly 13 , which consists of a rotationally symmetrical , downward tapering , truncated conical filter 14 , a rim of strip - shaped braking components 15 , and a membrane 16 . the membrane 16 has a round hole 17 which forms the outlet for the filtered and compacted fiber stock . the membrane 16 is located at the lower end face of the filter 14 , and can be made of an elastic metal , rubber , flexible synthetic material , or an equivalent material . a conveyer screw 19 is disposed in the interior of the filter 14 of the fiber filtering assembly 13 . the thread of the conveyer screw lies circumferentially adjacent to the filter 14 appropriately constructed of perforated sheet metal , wherein the hollow cylindrical shaft 20 of the conveyer screw 19 carries thread 21 , and possesses a large diameter which is only slightly smaller than the inside diameter at the smallest circumference of the filter . a shaft trunnion 22 is coaxially attached to the shaft 20 , which shaft trunnion is carried rotationally fixed but axially movable within the output component 24 of an electromagnetic coupling 23 , whose input - side component 25 is attached to the motor shaft 26 of an electric motor 27 serving for the propulsion of the conveyer screw 19 . thus , the conveyer screw 19 can perform axial stroke movements relative to the coupling 23 . the weight of the conveyer screw 19 is partly relieved by means of pressure spring means 29 acting against the bottom of a plate 30 rotatably affixed to the shaft trunnion 22 , which pressure spring means are disposed upon a stationary abutment 31 , so that the conveyer screw 19 rests with only a part of its weight on the filter 14 . the remaining part of its weight is supported in the axial direction , so that the thread 21 of the conveyer screw 19 grazes or touches lightly the filter 14 , conveying the fibers filtered at its inner side in the direction of the membrane 16 and along it to the outlet formed by the hole 17 of the membrane 16 for the filtered fiber stock , wherein the membrane 16 brakes the axial motion of the fiber stock and thus also forms a braking component causing the compaction of the fiber stock in cooperation with the braking components 15 . the air inlet duct 32 is disposed at the circumference of the air inlet component 11 , and preferably communicates tangentially with an annular chamber 34 , formed internally by a hollow cylinder 33 in the air inlet component 11 , so that the entering air flow is forced into rotation , namely in such a way as to rotate in an opposite sense relative to the direction of rotation of the conveyer screw 19 . this construction guarantees an air current inflow meeting a low resistance into the spiral chamber 35 . the air flow is dimensionally bound by the thread 21 of the conveyer screw 19 , and flows through the upper open end face of the filter 14 . the air to be filtered then flows through the holes of the filter 14 from the inside to the outside , whereby the fibers and the other coarser contaminants are filtered . the filter 14 is therein preferably constructed in such a way as to permit the throughflow of dust so as to filter the fibers without any interposing dust . the dust can then be filtered later in a conventional dust filter . the clean air liberated from the fibers then flows to the air outlet 36 located at the circumference of the main housing component 12 in the proximity of its lower end face , and flows through the air outlet 36 and out of the housing 10 . the air can be conducted through the filtering apparatus both by blowing and by suction . the conical configuration of the filter 14 possesses many advantages relative to cylindrical filters , for example , in a cylindrical filter air enters through its front face and as a result a static pressure is built up due to the decrease in the velocity of the air in the direction of the other end face of the filter , which static pressure causes the major part of the air to leave the filter in the proximity of this other end , to the effect that the throughflow through the filter is unevenly distributed . this effect is avoided by the conical configuration of the filter 14 , so that an even throughflow through the filter at all its points is achieved . the conicity of the filter can be selected preferably such as to cause the throughflow through the filter to be larger per unit of filter surface area at the end having the greatest diameter , and to cause the throughflow per unit of filter surface to diminish in the direction toward the other end , so that the end region of the filter , neighboring the outlet for the fiber stock and serving for the compaction of the fiber stock , is no longer strongly acted upon by the flowing air even when the filter is still empty . consequently , a nearly even pressure drop of the air at the filter is always obtained from the beginning of the operation on . it will be observed that the concept of the invention has utility with conical filters as well as considerable advantages with other types of configurations of the filter . the thread 21 of the conveyer screw 19 ends at 37 in the clearance above the membrane 16 , and in the region between this lower end 37 and the membrane 16 the braking components 15 are located at the inner wall of the filter 14 . the braking components 15 are constructed in the form of radically inwardly directed strips extending in the direction of the surface lines of the filter , and reaching close to the circumference of the shaft 20 , so that no rotation of the fiber stock conveyed to the bottom by the conveyer screw 19 can take place within the region of the braking components 15 . eight such braking components 15 can , for example , be distributed around the circumference of the shaft 20 , wherein an equal angular distance between the adjacent braking components is maintained . the braking components 15 thus prevent the rotation of the compacted fiber stock , and the membrane 16 effects the axial braking of the fiber stock . if necessary , the axial braking can also be effected by the face of at least one other rigid , braking components . the braking components 15 also effect the axial braking with their upper surfaces , and this function can be further amplified by broadening these braking components 15 . since the filtered fiber stock consists of fibers that are tangled with each other and thus possesses a compact consistency , the braking effected by the braking components 15 also acts upward against the thusly interconnected fiber stock which is continually being conveyed downward , so that it too does not rotate , and is hence continually pressed downward and compacted by the rotation of the conveyer screw 19 . thus , a strongly compressed and compacted fiber mass , whose cohesion is increased by the mutual entanglement of the fibers , forms in the lower region of the filter 14 , which fiber mass also contains the other filtered coarser contaminants such as shell remnants or equivalent materials , and which is continually pressed axially against the membrane 16 through the rotation of the conveyer screw until , at sufficiently large pressures , it bends the membrane downward , thus opening the outlet 17 . the membrane 16 thus offers a considerable resistance to expulsion of the fiber mass , in order to intensify substantially the compaction of the fiber stock , and the membrane also deflects the fiber stock into the outlet 17 . the fibers or equivalent materials filtered further upward within the filter need not yet possess a compact consistency , since they are continually conveyed downward by the conveyer screw even when they are moving in the direction of the circumference of the filter 14 , since that motion occurs in every case at a lesser rotational velocity than that of the conveyer screw , because these fibers are constantly flung toward the filter 14 by the air flowing through the filter , and their axial motion is thus also braked . it is also an advantage of this filtering apparatus that optimally large filters can be accommodated for any given proportional housing dimensions , so that it can filter very large air quantities per unit time , and hence is extremely efficient . the propulsion motor 27 can drive the conveyer screw 19 preferably continuously , so that the filter 14 is cleaned continuously and practically no pressure fluctuations of the air flowing through the filter are produced by the fiber stock filtered at the filter 14 , and thus a uniform air throughput is achieved at a minimal propulsive output for the conveying of the air , which is extremely advantageous . the free lower end face 39 of the conveyer screw 19 is conically constructed , and protrudes through the membrane opening 17 , wherein the membrane 16 is pressed downward by this cone - shaped end 39 , so that so long as no compressed fiber stock is present between the membrane 16 and the cone - shaped end 39 of the shaft 20 , the membrane lies snugly against this end 39 of the shaft 20 and therewith forms an air - tight closure . if , during operation , the fiber stock is continuously pressed into the outlet 17 , the fiber stock presses the membrane 16 downward and thereby fills the ring slot created between the membrane 16 and the end face 39 of the shaft 20 tightly , so that no air can flow from the outlet 17 , irrespective of the fact that compressed fiber stock is then also still present above the outlet 17 , where it acts like a stopper . the compacted fiber stock forms a strongly compressed fiber mass , which , after leaving the outlet , does not increase its own volume , or increases it relatively little , so that compressed fiber stock collects in the collecting sack 38 hanging beneath the outlet 17 of the housing . as a result , the sack 38 can hold large quantities of filtered fiber material without the requirement of any additional compaction devices . in some cases the depicted braking components 15 can also be omitted , namely when the compacted fiber stock is prevented from rotating synchronously with the conveyer screw 19 by the filter 14 , and / or by the membrane 16 , that is to say , when the membrane 16 and / or the filter 14 alone suffice to serve as the braking components . however , it is better to provide braking components , such as 15 , which protrude into the compacted fiber stock . as a result of the cohesion of the compacted fiber stock , it is in many cases also possible and appropriate to place braking components outside of the fiber filtering assembly 13 beneath its outlet , as indicated in fig1 by the dash - dotted lines . the rim of radial strip - shaped stationary braking components 15 &# 39 ;, whose radial orientation is relative to the conveyer screw , protrude under the outlet opening 17 to a proximity with the end face 39 of the shaft 20 . as a result , the components 15 &# 39 ; prevent the rotation of the fiber stock leaving the outlet 17 . this retardation of the rotation of the fiber stock is also propagated through the outlet 17 to the interior of the fiber filtering assembly 13 , in consequence of the cohesion of the fiber stock , such that here too a braking sufficient for an intensive , uniform compaction of the fiber stock is achievable . where appropriate , the braking components 15 and 15 &# 39 ; can be provided in combination . the propulsion unit of the conveyer screw 19 is graphically represented in an enlarged view in fig2 . the electric motor 27 is mounted on a disc 40 . the disc 40 has several slots 41 extending in a circumferential direction , which slots are penetrated by bolts 42 attached to a stationary plate , so that the disc 40 carrying the motor 27 can rotate restrictedly . a tension spring 44 , held by a support 43 attached to the disc 40 , is mounted with its other end on a stationary bolt 45 , and thus urges the disc toward the view depicted in fig2 which corresponds to the normal operational position . when the torque delivered by the motor exceeds a predetermined value , as may be called forth by an unacceptably severe congestion of the fiber stock 14 , by a jamming of the conveyer screw in the filter 14 ; then the disc 40 rotates in opposition to the restoring force of the spring 44 , and thus actuates a stationarily disposed electrical switch 47 , which closes a current circuit which triggers a suitable action , for example , switching off of the motor 27 and triggering of an alarm signal to summon an attendant , or of reversing the rotational direction of the motor shaft . in the last case , the conveyer screw then rotates clockwise as viewed from its top , thereby transporting the congested fiber stock upward so that this congestion is loosened , wherein a timing switch can be provided which once again switches the propulsion motor 27 to its normal rotational shaft direction after a preselected period of time . in this manner , excessively severe congestion can be loosened automatically , whether it be through a single , or through a repeated reversal of the rotational direction of the motor 27 . a further safety feature is additionally provided in this filtering apparatus , for the loosening of a congestion , which functions through the actuation of a stationary switch 47 &# 39 ; by a rod 46 attached to the shaft trunnion 22 . when the conveyer screw 19 is pressed axially upward due to a congestion , which can , for example , occur when the sack 38 is full . this switch 47 &# 39 ; can also either switch the motor 27 off and trigger an alarm , or else reverse the rotational shaft direction of the motor 27 . for this purpose the rod 46 is mounted in a conventional manner to the shaft 22 so that it is retained in alignment with the switch 47 &# 39 ;. alternatively , the rod 46 could be a plate which rotates with the shaft 22 . the exemplary embodiments according to the fig3 and 4 can , with the following differences , correspond to the filtering apparatus according to fig1 and 2 . the differences consist in the fact that the diameter of the shaft having the thread 21 of the conveyer screw 19 is substantially smaller than the diameter of the lower end of the conical filter 14 of the fiber filtering assembly 13 , and further that a cylindrical housing component 48 is coupled to the lower end face of the filter 14 , and that two rims of radial and axially extending plate - shaped braking components 15 , 15 &# 34 ; are arranged in the interior of the fiber filtering assembly 13 . the screw thread 21 ends at the lowest face surface of the filter 14 . the upper braking components 15 &# 34 ; end at this lowest face surface . these braking components 15 &# 34 ; are attached to and extend along the lower section of the filter 14 , reaching inward almost to the thread 21 of the conveyer screw 19 , wherein the diameter of the thread 21 is correspondingly decreased within the region of the braking components 15 &# 34 ;, since they must not engage with the threadways of the conveyer screw 19 because the rotation of the conveyer screw does not permit it . the other rim of similarly radial plate - shaped braking components 15 extending axially in the direction of the conveyer screw is located in the lower , cylindrical part of the housing 12 , and in this preferred exemplary embodiment a considerable distance is provided between these braking components 15 and the radially proximate and cylindrical region of the shaft 20 of the conveyer screw 19 , wherein each intervening space between these braking components 15 and the shaft 20 possess an approximately triangular shape , in such a manner that this intervening space tapers from top to bottom , which has been shown to be particularly favorable . the outlet 17 is again formed by a hole in the membrane 16 . the membrane can , for example , consist of a rubber sheet having a thickness of a few millimeters , which sheet can be reinforced by cloth . so long as no fiber stock is present in the outlet 17 , the membrane 16 lies air - tight against the likewise conical end face 39 of the shaft 20 of the conveyer screw 19 . as soon as the fiber stock is pressed into the outlet , the membrane 16 bends correspondingly downward to open the outlet , and always serves to assure that the compressed fiber stock is pressed through the outlet 17 , which fact further increases the compaction effect of the conveyer screw . these braking components 15 , 15 &# 34 ; retard particularly intensively the rotation of the compacted fiber stock , wherein as a result of the relatively long braking components 15 &# 34 ; inside the filter 14 , the fiber stock is hindered directly by these braking components 15 &# 34 ; in its rotation , up to the corresponding level in the fiber , so that even under unfavorable conditions practically no rotation of the compacted fiber stock can take place . in this exemplary embodiment , each rim of braking components 15 , 15 &# 34 ; has eight braking components , as seen in fig4 . in addition , the braking components 15 , 15 &# 34 ; which are grouped one above the other group , are also paired and aligned axially , which is useful . however , in a given case , the two rims of braking components 15 , 15 &# 34 ; can be respectively offset angularly , and / or possess mutually differing numbers of braking components . although , as mentioned , it is particularly advantageous to construct the filter in the form of a cone , other configurations of the filter can be provided . thus , in the exemplary embodiment according to fig5 the filter 14 &# 39 ; of the fiber filtering assembly 13 is cylindrical and is clamped at its top by a flange between an air inlet component 11 and a main component 12 of the housing 10 . the embodiments according to fig1 - 4 are valid for the housing 10 and the propulsion of the conveyer screw 19 in the embodiment according to fig5 . in this exemplary embodiment , the membrane 16 lies against a flat surface 39 &# 39 ; of the shaft 20 , so long as the membrane is not pressed down by fibers . in this exemplary embodiment part of the weight of the conveyer screw 19 is similarly relieved by means of a weight relieving device , and so the conveyer screw can be supported by the membrane , or it can be provided that the lower axial terminal position of the conveyer screw 19 be determined by means of an axial pressure bearing located in the output component 24 of the coupling 23 . the partial relieving of the weight of the conveyer screw 19 , effected by the spring means 29 , serves in particular to insure that the conveyer screw 19 moves upwardly during an axial congestion of the fiber stock so that actuation of the switch 47 &# 39 ; can occur . this actuation occurs sooner than would be the case in the absence of weight relieving . in this exemplary embodiment , inwardly directed plate - shaped braking components 15 &# 34 ; reaching almost to the screw thread 21 are likewise provided within the filter 14 &# 39 ; along its lower end region . the diameter of the applicable thread region of the thread 21 is correspondingly decreased in the region of the braking components 15 &# 34 ;. in addition , the screw thread extends almost to the membrane 16 in this exemplary embodiment , which fact can be useful especially during very large fiber yields . the braking components 15 , 15 &# 39 ; and 15 &# 34 ; in this and the other exemplary embodiments need not necessarily be constructed in the form of strips or plates , but can rather also possess other suitable shapes . also the plates or strips forming the braking components need not in all cases extend radially , that is along surface lines of the cylinder . rather , they can , if need be , be angularly inclined relative to the diametric planes of the conveyer screw and thus likewise effect a good braking of the fiber stock . in the preceding exemplary embodiments , the conveyer screw 19 had respectively a thread 21 of constant pitch . however , in many cases threads of varying pitch can be provided , as depicted in the example according to fig6 . this exemplary embodiment according to fig6 differs with the one according to fig5 due to the fact that the pitch of the thread 21 &# 39 ; of the conveyer screw 19 is not constant , but rather decreases uniformly in the direction of the outlet 17 of the fiber filtering assembly 13 . with a decreasing pitch , the axial conveying velocity of the conveyer screw 19 correspondingly decreases uniformly in the direction toward the outlet 17 . this is often advantageous , since the delivery of the fibers filtered at the filter 14 &# 39 ; to the compaction zone for the fiber stock , created by the braking components 15 &# 34 ; and the membrane 16 , therefore takes place at a velocity which decreases in the direction of that compaction zone , and since thus the fiber stock is correspondingly compacted still more , due to the fact that it is expelled from the outlet 17 at a lower velocity . the filtering apparatuses described above are suitable , among other uses , for filtering systems wherein they follow preliminary filters . on the other hand , both of the filtering apparatuses illustrated , according to the invention , in fig7 - 11 serve preferably for the direct filtering of air in pneumatic exhaust systems of spinning machines . they feature , respectively , a box - shaped housing 10 &# 39 ; containing a ventilator 50 which conveys the air to be filtered , and which can be the only ventilator of the given particular exhaust system , and which is a suction ventilator . these filtering apparatuses are thus preferably intended for the purpose of both exhausting the air at spinning machines with exhaust systems , as well as of filtering and automatically compressing the fibers , thread remnants , and equivalent materials , carried by the exhausting air , and to deposit them in a respective collecting chamber 51 in the housing 10 &# 39 ;. one can also designate these filtering apparatuses as being filtering boxes . in the embodiment according to fig7 - 9 , the fiber filtering assembly 13 , and the conveyer screw 19 rotating therein , are , in principle , constructed as illustrated in fig5 and require no further discussion . it is only noted that , in this exemplary embodiment , the propulsion motor 27 provided for the conveyer screw 19 is located in a separate compartment 70 in the housing 10 &# 39 ;. the air flows into the housing 10 &# 39 ; through the large rear inlet 32 &# 39 ;, to which connects a feeder duct 77 . the air drawn into the housing 10 &# 39 ; first reaches the upper throughflow chamber 52 , which is separated by an intervening base 53 from the throughflow chambers 54 , 55 located thereunder . a single hole 56 is provided in the itervening base 53 , with which hole 56 the open face of the cylindrical filter 14 &# 39 ; communicates , so that the air is drawn into the filter 14 &# 39 ; from the upper chamber 52 , and then through the filter and into the throughflow chamber 54 bound respectively on top and on the bottom by the intervening base 53 and the base of the housing . the throughflow chamber 54 is bound on the inside by a vertical intervening wall 57 , into which the ventilator 50 is set with its suction opening . the impeller 59 of the ventilator 50 is located in the rear chamber 55 separated from the chamber 54 by the intervening wall 57 , and is itself located beneath the intervening base 53 . the impeller 59 drives the air through this chamber 55 , from which it flows through a bottom opening 60 . this bottom opening 60 can be aligned to communicate with an opening in the floor of the room of the given building , and can , for example , lead to an air exhaust duct of the climate system of the given building . the fiber stock filtered and compacted in the fiber filtering assembly 13 reaches the collecting chamber 51 , separated from the chamber 54 by an air - tight wall 61 , through the outlet 17 of the membrane 16 , from which collecting chamber 51 the fiber stock is removed , for example , manually , from time to time . in this exemplary embodiment , the conveyer screw 19 is oriented vertically . in the preceding exemplary embodiments , the respective interior of the fiber filtering assembly 13 is constructed to be rotationally symmetrical , which is exceedingly advantageous . however , it is also possible to construct it differently , preferably to construct it to be rotationally symmetrical only over a part of its axial length , and in particular to construct it rotationally not symmetrically in the end region neighboring the outlet for the fiber stock . thus it can , for example , be useful in many cases to make the circumferential wall of the fiber filtering assembly rotationally non - symmetrical in the vertical region of the braking component or components , and instead construct it , for example , star - shaped in cross section featuring at least one inwardly directed spike . such a spike , or the inwardly directed regions of the star - shaped pattern , can then be formed by braking components , which inhibit the rotation of the compacted fiber stock . under some conditions a solely polygonal figure , for example , a square , triangle , or other polygonal figure of the circumferential wall of the compacted zone of the fiber filtering assembly also suffices to exert a sufficient braking effect upon the compacted fiber stock , wherein this region of the fiber filtering assembly can be constructed by means of an airproof wall and / or by means of a section of the filter . in the exemplary embodiments according to fig1 and 11 , the conveyer screw 19 is located in the box - shaped housing 10 &# 39 ;, and its axis of rotation is horizontal . departing from the preceding embodiment , the fiber filtering assembly 13 is not constructed rotationally symmetrical , but rather formed by the flat exterior wall regions 62 , 63 and 64 of the box - shaped housing 10 &# 39 ;, and by the flat interior wall regions 65 , 66 in the housing 10 &# 39 ;, as well as by a filter 14 &# 34 ; which is circular in shape and which extends in this exemplary embodiment over a radial sector of approximately 120 degrees , and by a face wall 65 &# 39 ; containing the membrane 16 . the conveyer screw 19 grazes this filter 14 &# 34 ;, and is driven by an electric motor 27 located in a separate compartment 70 of the housing 10 &# 39 ;. a throughflow chamber 67 in the housing 10 &# 39 ; mates to the exterior of the filter 14 &# 34 ;, and a side wall 68 located approximately in the middle of the housing 10 &# 39 ; contains the suction opening of the ventilator 50 , the impeller 59 of which blows air through the throughflow chamber 71 and downward and out through an air outlet 60 in the base of the housing 10 &# 39 ;. the air inlet 32 &# 39 ; of this housing 10 &# 39 ; is located at the rear wall of the housing 10 &# 39 ; and communicates directly with the fiber filtering assembly 13 . in this exemplary embodiment , that given circumferential region of the conveyer screw 19 which does not lie next to the filter 14 &# 34 ; , is situated at some distance from the airproof wall regions 62 - 66 . the air drawn into the filter 14 &# 34 ; flows into the fiber filtering assembly 13 preferably perpendicularly relative to the rotational axis of the conveyer screw 19 , and through it to the filter 14 &# 34 ;. since this air flows into the conveyer screw over its entire free circumference , it inhibits the co - rotation with the conveyer screw of the fibers conveyed by the conveyer screw 19 , so that the fibers are already conveyed along the filter 14 &# 34 ; by the conveyer screw 19 , and are already compacted in the region ahead of the outlet 17 due to the resistance offered by the membrane 16 forming the outlet 17 . the membrane 16 can be constructed and arranged according to the preceding exemplary embodiments . thus , compacted fiber stock is formed which falls into the volumetrically large collecting chamber 51 extending over the entire interior height of the housing 10 &# 39 ;, where it can be manually removed , from time to time , through an opening . the door which normally closes this opening is represented by the dash - dotted line 74 . the braking components for the braking of the rotation of the fiber stock can , in this exemplary embodiment , be formed solely by the filter 14 &# 34 ; and the membrane 16 , wherein the air flowing into the filter 14 &# 34 ; cooperates to prevent the co - rotation with the conveyer screw 19 of the fibers present at the filter 14 &# 34 ; and strongly compacted in the vicinity of the outlet 17 . however , if required , one or several additional braking components can also be provided . for example , according to fig1 , a radial stip 15 &# 39 ;&# 34 ; extending axially relative to the conveyer screw 19 and reaching from an edge of the wall of the fiber filtering assembly 13 toward and close to the conveyer screw 19 or grazing it , can usefully serve as the braking component , so that the fiber stock which reaches the space between the filter 14 &# 34 ; and this strip 15 &# 34 ;&# 39 ; is accumulated by this strip , and thus is certainly prevented from rotating , without being hindered in its motion in the axial direction of the conveyer screw 19 . this accumulated fiber stock also prevents the rotation of other adjacent fiber stock with which it is entangled . this braking component 15 &# 39 ;&# 34 ; can preferably extend along the entire conveyer screw 19 , or it can also extend only opposite the end section of the conveyer screw 19 , generally located in the vicinity of the outlet 17 . in the depicted exemplary embodiments , the fiber filtering assembly 13 has respectively one single filter . however , where appropriate , the fiber filtering assembly can also have several filters , for example , two or more mutually mating filters , or else filters that are mutually offset in the direction of the circumference . in addition , where appropriate , several such fiber filtering assemblies can be arranged in parallel or else one after the other in series . in all of the preceding exemplary embodiments , the membrane 16 serves , among other purposes , for the axial braking of the compacted fiber stock . at its location other braking components , which brake the axial motion of the fiber stock , can also be provided , for example , transverse ribs or bends in the lower ends of the projections 15 , or a rigid , preferably conical ring at the corresponding end face of the fiber filtering assembly . in the event that braking surfaces braking the rotation of the compacted fiber stock already create a sufficient degree of compaction , then the end face of the fiber filtering assembly neighboring these braking surfaces can also be open . the invention also makes possible an automatic regulation of the pressure drop at the filter , wherein this pressure drop is sensed by a differential pressure sensor device , and is compared to a specified and preferably adjustable reference value to generate a reference deviation value , whereby the rotational velocity of the propulsion of the conveyer screw is automatically and preferably continuously variable in accordance with that reference deviation value , in order to regulate the pressure drop at the filter , wherein an automatic chronological stopping of the conveyer screw can preferably occur as well . in some circumstances , a two - point regulation can also be provided , wherein the propulsion of the conveyer screw is regulated by the regulator alternately to stop and to run for a single rotation .