Device for removing material screened or filtered out of a liquid flowing in a channel

A device for removing material screened or filtered out of a liquid flowing in a channel (3), especially in waste water treatment plants, is described. The device comprises an unpowered cylindrical grating surface (8) being immersed partly in the liquid and being formed by a plurality of substantially semicircular grating bars (10) located with distance to each other. The device further comprises a removing beam (12) rotatably driven about the axis (2) of the grating surface (8) and having removing elements (15) extending between the grating bars (10) from the inside of the cylinder to the outside. A conveying device (17) for the material is provided which is positioned with respect to the grating surface (8) and leads to a point outside the liquid in the channel (3), the device having a tube-like housing (22) with an opening (23) for the entry of the material and a driven screw (20) inside the housing (22). The unpowered at least about semicircular formed grating bars (10) of the grating surface (8) are positioned with their convex surfaces facing the flow direction (5) of the liquid in the channel (3) so that the material is deposited on the outside of the grating surface (8). The removing elements (15) on the removing beam (12) extend from the inside of the cylinder to the outside between the grating bars (10) in the direction opposite to the flow of the liquid according arrows (29) through the slots (11) between the grating bars (10).

FIELD OF THE INVENTION 
The invention relates to a device for removing material screened or 
filtered out of a liquid flowing in a channel, especially in waste water 
treatment plants. Although the device is especially intended for water 
treatment plants, it can also be employed in a practical way in other 
fields of technology, in the textile and plastic industries, in 
slaughter-houses, in poultry farms, in tanneries, etc., for example, in 
order to remove material, i.e. sieve or raking material, out of the 
liquid. 
BACKGROUND OF THE INVENTION 
A device of the type mentioned above is known from DE 40 06 970 A1. The 
semicircular grating bars of the grating surface are fixed to each other, 
fixly mounted and form a grating surface with its inner concave surface. 
The grating bars extend only partly about the lower part of the 
circumference. The part of the cylinder which is not covered by the 
grating bars is closed by a covering in form of a semicylindrical wall or 
sheet steel. The front side of the cylinder id designed open to make the 
entry of the liquid including the material possible. The liquid flows 
through the grating surface from the inside to the outside of the cylinder 
so that the material is deposited on the inside, i.e. on the concave side 
of the grating bars. A removing beam having removing elements is rotatably 
driven around the axis of the cylinder. The removing elements of the 
removing beam extend in a comb-like fashion into the slots between the 
grating bars from the inside to the outside and gathers the material 
during revolution. A conveying device is arranged outside the cylinder of 
the grating surface, the conveying device comprising a tube-like housing, 
a shaft and a screw on the shaft. The conveying device has an opening for 
the material to enter. The tubelike housing is designed closed with the 
exception of the inlet and outlet. A space is provided between the 
coverings in sheet steel form and the beginning of the semicircular 
grating bars. The space serves for the transition of the material from the 
grating surface to the conveying device. In the region of transition of 
the material a comb-like stripper is arranged. Changing the direction of 
revolution of the removing beam a stripping effect occurs loosening the 
material from the removing elements of the removing beam so that the 
material falls into the opening of the conveying device. It is not evident 
where the liquid level of the oncoming liquid is positioned. Due to the 
fact that the entry of the liquid only is possible through the front 
surface of the cylinder and a part of the grating surface as large as 
possible should be used for depositing of the material on the grating 
surface the liquid level should be arranged in an adapted height. However, 
in this case, at least a large part of the opening of the conveying device 
is positioned below the liquid level so that the material loosened can 
fall only from the comb-like stripper into the liquid. Since the housing 
of the conveying device is designed in closed manner the flow of the 
liquid can only happen in the region of the grating surface so that the 
danger results that the material loosened from the comb-like stripper 
falls down into the liquid again and again without being removed out of 
the channel. Thus, a concentration of material results on the grating 
surface. If, however, the liquid level is chosen much lower the opening of 
the conveying device is prepared to take over material, but in this case 
the effective area of the grating surface is substantially reduced and the 
effectivity is decreased. The disadvantages described depend on the height 
of the liquid level. It is a further disadvantage that the removing beam 
and the removing elements cooperate with the inner circumference of the 
semicircular grating bars. The removing beam is positioned facing the 
concave side of the grating surface, i.e. in a place in the liquid, in 
which the liquid contains the material. From this the danger results that 
the material will deposit on the removing beam generating stricks of the 
material. It is a substantial disadvantage that the removing elements of 
the removing beam penetrate the grating surface in the direction of the 
flow of the liquid through the grating surface. Thus, a substantial part 
of the material is pressed through the slots between the grating bars, 
this part of the material remaining in the liquid so that the cleaning 
effect of this device is limited. 
Another device for removing material out of a liquid flowing in a channel 
is known from DE 30 19 127 C2. Here also grating bars fixly connected to 
each other are used to form a grating surface, the grating bars extending 
over a circumference of about 270.degree. of the cylinder. Here also the 
liquid flows through the slots between the grating bars from the inside to 
the outside, i.e. the concave side of the grating bars is facing the 
oncoming liquid in the channel. The liquid enters the interior of the 
cylinder via the open front side. A removing beam having removing elements 
cooperates with the grating bars. The drive of a conveying device is used 
to drive the removing beam. The conveying device having a housing, a shaft 
and a screw is positioned coaxially with respect to the axis of the 
cylinder. Again, the opening in the housing of the conveying device is 
located below the liquid level and partly even apart from the falling zone 
of the material so that the danger results that the material is deposited 
on the grating surface and falls back into the liquid and is again 
deposited on the grating surface and so on instead of being guided into 
the conveying device. Here also the effect of pressing parts of the 
material through the slots between the grating bars occurs. This part of 
the material remains in the liquid and is not removed. 
It is the object of the invention to improve a device of the type initially 
described which can be used in channels of different depth and with 
differing liquid levels and which allows a proper removing of material 
independent from different conditions. 
According to the invention this is achieved with a device of the type 
mentioned above, wherein the unpowered at least about semicircular formed 
grating bars of the grating surface are positioned with their convex 
surfaces facing the flow direction of the liquid in the channel so that 
the material is deposited on the outside of the grating surface, the 
removing elements on the removing beam extend from the inside of the 
cylinder to the outside between the grating bars in the direction opposite 
to the flow of the liquid according arrows through the slots between the 
grating bars, the part of the cylinder not covered by the semicircular 
grating bars is designed open, and the conveying device is positioned with 
its axis slanting downwardly to the bottom of the channel. 
The invention starts with the idea to let the liquid flow through the 
semicircular grating bars from the outside to the inside of the cylinder. 
The material is deposited on the convex surface of the grating bars. The 
front surfaces of the cylinder are closed so that the liquid can enter the 
interior of the device only by a passage through the slots between the 
grating bars from the convex outer surface to the concave inner surface. 
The semicircular grating bars are positioned with the convex surface 
facing the oncoming liquid in the channel, while in the prior art the 
concave surface is facing the oncoming liquid flow. By this change the 
advantage results that there is no longer a dependency on the principle 
limits of the devices known in the prior art, i.e. the grating surface can 
be used in an optimal way independent from the changing liquid levels. The 
slanting downward positioning at least of the conveying device can be 
varied and adapted to the special conditions. The device does not need 
much room in the channel. It is especially advantageous to position the 
grating surface with its axis vertically in the channel so that a very 
short length of the device in the channel results. A further substantial 
advantage is the possibility of standardizing. It is possible simply to 
add or to remove grating bars and elements of the removing beam in order 
to adapt the device to the conditions of the application. Thus, it is 
possible to mount the device from single elements in foreign countries far 
away from the production plant. 
The grating bars of about semicircular form extend over half the 
circumference of the cylinder, i.e. over 180.degree., and have 
prolongations at both ends. Each of the grating bars has the shape of a 
walking stick, wherein the prolongations may have different length. The 
prolongation facing the conveying device is designed longer than the 
prolongation on the other side. The axles or bars to take up and hold the 
grating bars with intermediate distance pieces are located in the area of 
the prolongations. Thus, The axles and the distance pieces do not prevent 
rotating of the removing beam with the removing elements. On the other 
hand this kind of bearing of the grating bars is sufficient to hold the 
grating bars in the predetermined distance to each other in the 
semicircular part. The removing elements enter the slots between adjacent 
grating bars in the vicinity of an axle or bar so that this is a place 
where the distance is fixly adjusted by the height of the distance pieces. 
During revolution the removing elements can have contact with the 
semicircular grating bars which are elastically held in their mutual 
relationship. This is not disadvantageous because wear makes production 
tolerances to disappear in a self-correcting manner. At the line in which 
the free ends of the removing elements are withdrawn from the convex 
surface of the grating bars a transfer of the material from the removing 
elements to the grating bars occur without the need of a special loosening 
element. The flow of the liquid is used at this line to convey and guide 
the material into the conveying device. 
The transition line of the material from the removing elements to the 
conveying device is located below the liquid level. This is a substantial 
advantage and offers the possibility to use the flow of the liquid as a 
loosening element and a transport vehicle for the material. For this 
purposes the housing of the conveying device has to be designed with holes 
distributed over the axial length of the opening in the housing. Thus, the 
liquid flows not only through the grating surface but also through the 
housing of the conveying device in order to favour the transfer of the 
material from the end of the grating surface into the interior of the 
conveying device and to prevent a second depositing of the material on the 
grating surface. The flow of the liquid is used advantageously. The 
material is concentrated in front of the opening of the housing of the 
conveying device. This concentrated material is taken by the screw under 
the liquid level and guided upwardly over the liquid level. Parts of the 
liquid flow back in the channel through holes in the housing of the 
conveying device. 
A further substantial advantage of the invention is the fact, that the 
shaft of the removing beam and the removing elements work on the clean 
side of the liquid. This prevents a depositing of material on the removing 
beam and the removing elements. At the same time an effect of pressing 
parts of the material through the slots between the grating bars is 
avoided, because the removing elements act through the grating surface in 
a direction opposite to the direction of flow of the liquid. The removing 
elements penetrate through the slots from the inside to the outside of the 
cylinder and extend over the outer surface of the grating bars in order to 
make the gripping and gathering of the deposited material possible. 
Swimming material is not pressed through the grating surface but deposited 
on the convex side of the grating surface. 
The conveying device has a substantial washing effect for the gathered 
material in moved below the liquid level and guided to that part of the 
housing of the conveying device having holes. 
The invention offers the advantage of standardization of the two units of 
the device, i.e. a conveying device having a predetermined diameter can be 
used in conjunction with depositing units having different diameters of 
the cylinder and the grating bars. The conveying device is a separate 
construction element which has to be located with respect to the 
depositing unit only as far as local arrangement is concerned. It is not 
necessary to connect the two units with each other. The new device can be 
used for different applications, for example also if it is the liquid 
which has to be cleaned. The device can be used in very deep channel 
having only a normal width. 
A connection wall may be provided between the semicircular grating bars and 
the opening of the housing of the conveying device. The cylindrical 
grating surface with the axis and the conveying device with the axis are 
designed to be positioned in different angles with respect to the channel. 
The connection wall may extend below the conveying device. The connection 
wall may be designed closed, for example by a sheet steel. However, the 
connection wall may consist of the walking-stick-like prolongations on the 
semicircular grating bars and thus constructed open. In all cases the 
connection wall is a plane area arranged tangentially to both, the grating 
bars and the housing of the conveying device. Thus, the advantage results 
to position the grating surface independent from the positioning of the 
conveying device in the channel and to combine these both units. It is 
especially advantageous to position the grating unit with its axis 
vertically and the conveying device with its axis slanting downwardly. 
The housing of the conveying device may be provided with holes distributed 
over the axial length of the opening. This favours the entry of the 
material gathered by the removing elements into the opening of the 
conveying device. 
The semicircular grating bars of the grating surface with the use of 
distance pieces may be mounted and held replaceably in spaced relationship 
on axles. This gives the simple possibility of standardization. The 
adaptation may be performed at the place where the device shall be used. 
On the other hand the elements of the grating surface can be produced in 
series and at low costs. The use of distance pieces, especially in form of 
disks, gives the simple possibility to generate slots of different width 
using the same grating bars. The only need is to have distance pieces of 
different height. This can be done from device to device, but also inside 
a single device, to have the grating surface divided in parts having 
different width of the slots. It is useful to have a smaller width of the 
slots in the lower region of the grating surface, while in the upper 
region of the surface an emergency part can be provided having a larger 
width of the slots. The liquid with low liquid level is cleaned carefully. 
Larger amounts of liquid with higher liquid levels may pass the device 
quicker due to the reduced hydraulic drag in the upper region having the 
larger width in the slots. Even an emergency overflow can be arranged. 
The housing of the conveying device may be designed in form of a sieve or a 
slitted wall extending at least over the axial length of the opening in 
the housing. Designing the holes in the lower part of the housing of the 
conveying device it is important to make the sum of the free areas 
sufficiently large to prevent pressing the flow into the direction of the 
grating surface. It is the desired flow of the liquid in the vicinity of 
the conveying device which is used to direct the gathered material into 
the conveying device instead into the grating surface of the grating unit. 
The connection wall may have a closed plane surface and may be positioned 
in the channel parallel to the flow direction. The connection wall may 
support the grating surface also. 
The removing beam with its removing elements may be composed from elements 
which can simply be replaced or completed. Thus, it is possible to adapt 
the removing beam and the removing elements to another axial length of the 
grating surface. 
It is possible to combine two grating surfaces with their removing beams 
driven in opposite direction with one common conveying device. It is 
evident that the opening in the housing of the conveying device has to be 
designed symmetrically with respect to a vertical plane in the middle of 
the channel in order to accept material from both of the grating units. In 
this way the device can be adapted to different width of the channels. 
The conveying device may comprise a pressing zone for the material, the 
pressing zone being arranged upstream to a chute. In this area the housing 
has also holes through which liquid pressed from the material in the 
pressing zone can flow back into the channel. In the pressing zone a 
stopper is generated from the compressed material. The material will fall 
down through a chute into a container or the like. 
The removing beam on the one hand and the conveying device on the other 
hand both may be equipped with separate drives. Thus separate unit are 
created which have to be mounted in local relationship only in the 
channel. It is not necessary to connect the individual drives. It is 
useful to control the drives separately. The circumferential speed of the 
removing elements can be chosen slower than the flowing speed of the 
liquid in the channel in order to make the loosening effect by the flow of 
the liquid more effective. Furthermore the times of revolutions and the 
times of standstill can be controlled separately and in different manner. 
The front surfaces of the cylinder-like grating surface are closed so that 
the liquid can enter the grating unit only through the grating surface. 
Positioning the grating surface with its axis vertically the front surface 
is closed by the bottom of the channel. Positioning the grating surface in 
a slanting downward manner a step in the bottom is necessary or something 
similar to close the front surface.

DETAILED DESCRIPTION 
A schematically shown side view of the device 1 with its essential elements 
is illustrated in FIG. 1. The device 1 is positioned with its axis 2 
slanting in the channel 3, of which only the bottom 4 and a side wall are 
shown. A liquid containing material to be screened of filtered flows in 
the channel 3 in flow direction 5. The liquid level in the channel can 
vary between limits. The drawing shows a comparatively low liquid level 6 
and a comparatively high liquid level 7. But the liquid level may be even 
higher or lower, for it depends upon rain showers for example. 
The device 1 comprises a grating surface 8 formed by a plurality of grating 
bars 10 extending half the circumference of a surface 9 of a cylinder. The 
grating bars 10 are illustrated schematically only. The grating bars 10 
are positioned along the height or the length respectively of the surface 
9 of the cylinder. The grating bars 10 are mounted with distance to each 
other so that slots 11 are formed between adjacent grating bars 10 for the 
passage of liquid. The liquid flows through the surface 9 of the cylinder 
from the outside to the inside due to the relative positioning of the 
semicircular grating bars 10 being positioned with their convex side in 
opposite direction to the flow direction 5. Thus, the grating surface 8 is 
provided on the outside of the surface 9 of the cylinder. The material 
contained in the liquid and to be removed will deposit on the outside of 
the grating surface 8 of the cylinder, while the liquid cleaned from the 
material will flow through the slots 11. The grating surface 8 formed by 
the half-cylindrical surface 9 of the cylinder is positioned with respect 
to a step in the bottom 4 of the channel 3, to direct the liquid to flow 
through the slots 11. It is clear that the bottom side of the 
half-cylindrical surface 9 and the connections of it to the side walls of 
the channel 3 are closed. These details are not shown for clarity. 
A removing beam 12 in shape of a shackle is fixly connected with a shaft 
13, the axis of which is positioned in the axis 2 of the device 1 and thus 
in the axis of the cylinder. The shaft 13 is supported in bearings (not 
shown for clarity). The shaft 13 extends over the liquid level and is 
driven by a schematically illustrated motor 14. The removing beam 12 is 
provided with removing elements 15 arranged with respect to the location 
of the slots 11 between the grating bars 10. The removing elements 15 
during rotation extend through the slots 11 between the grating bars 10 in 
a comb-like fashion from the inside of the cylinder to the outside. The 
removing elements 15 extend over the outside of the grating bars 8 in an 
extend to be sure to gather on the one hand all the material deposited of 
the outside of the grating bars 10 during one revolution of the shaft 13 
and the removing beam 12 and to deplace and convey on the other hand this 
gathered material in the direction to the side according to the direction 
16 of revolution of the removing beam 12. The conveying motion often 
occurs substantially below the liquid level 6 or 7 in the lower part of 
the semicylindrical surface, while in the upper part it happens that the 
gathered and conveyed material will be raised higher than the liquid 
level. But at the end of its semicircular conveying way this material will 
be pressed under the liquid level again. 
Displaced to the side (FIGS. 1 and 2) of the device 1 containing the 
grating surface 8 a separate conveying device 17 is provided which is 
positioned with its axis 18 slanting in the channel 3 also. The conveying 
device 17 is not connected with the device 1 neither with respect to a 
drive nor with respect to the elements of construction. The device 1 and 
the conveying device 17 may be completely separate units, only positioned 
with respect to each other in the channel 3. The conveying device 17 
comprises a shaft 19 (FIG. 2) equipped with a screw 20. A motor 21 
connected to the top end of the shaft 19 serves to drive the shaft 19 of 
the conveying device 17. A reduction gear may be provided between the 
motor 21 and the shaft 19. A further substantial element of the conveying 
device 17 is a tube-like housing 22 which is closed on the circumference 
of most of the length of the conveying device 17. Only in the lower part 
with respect to the axial length of the grating surface 8 or the 
semicylindrical surface respectively the housing 22 is designed with an 
opening 23 to pick up the material conveyed by the removing elements 15 
from the device 1. On the opposite side, downstream in the channel 3, the 
housing 22 has holes, slits or the like 24 for the liquid to pass. The 
holes, slits or the like 24 are located over the axial length or height. 
In the upper region of the conveying device 17 or the housing 22 a 
pressing zone 25 is arranged and located prior to a chute 26. In the 
pressing zone 25 the screw 20 is removed from the shaft 19 so that the 
shaft 19 extends up to the motor 21. The material screened, deposited, 
gathered, conveyed, and compressed is ejected through the chute 26 into a 
receptacle, a container, or into another conveying means. In the area of 
the pressing zone 25 the housing 22 may be provided with holes 27 (FIG. 
3), through which liquid from the compressed material will flow back into 
the channel 3. The holes 24 and 27 may have the same size and shape or a 
different form adapted to the purposes. 
As best seen from FIG. 2 the semicircular grating bars 10 with their one 
ends are in contact to the side wall of the channel 3. On their other ends 
the grating bars 10 may have extensions 28 forming a delivery line for the 
material deposited on the grating surface 8, and gathered and conveyed by 
the removing elements 15. The housing 22 of the conveying device 17 is 
positioned in a manner to contact the extensions 28 with its opening 23 
according to the relative position illustrated in FIG. 2. The extensions 
28 substantially are directed radially with respect to the axis 2 and in 
the flow direction 5 of the liquid in the channel 3. The liquid penetrates 
the slots 11 between the grating bars 10 in the direction of arrows 29. 
Due to the positioning of the openings 24 in the housing 22 of the 
conveying device 17 part of the liquid flow in the direction of arrow 30 
(FIG. 2). This flow direction is used to have a conveying motion 
transferred from the flowing liquid in the direction of arrow 30 to the 
material conveyed by the removing elements 15 and on delivery line of the 
extensions 28 and further into the interior of the housing 22 of the 
conveying device 17. The free ends of the removing elements 15 extend only 
with distance to the free ends of the extensions 28. The transport of the 
material from the removing elements 15 to the extensions 28 results from 
the shaping of these mechanical elements and the flow of the liquid in the 
direction of arrow 30. This happens below the liquid level, i.e. at a 
place where the liquid can show a transporting effect. Thus, the flow of 
the liquid in the direction of arrow 30 is advantageously used to convey 
the material into the conveying device 17 and in the area of the screw 20 
on the shaft 19, the material passing the opening 23 of the housing 22. 
The flow of the liquid in the direction of arrow 30 circulates the 
material and thus a washing effect occurs being increased by the motion of 
the screw 20 in the housing 22. In this manner organic parts are removed 
from the material so that these organic parts remain in the liquid, while 
the material removed by the conveying device 17 is cleaned by the washing 
effect. 
As illustrated in FIGS. 2 and 3 the grating bars 10 may be positioned on 
axles 32 with the help of distance pieces 31, the height of the distance 
pieces 31 determining the width of the slots 11. The axles 32 and the 
distance pieces 32 are located outside the revolving way of the free ends 
of the removing elements 15. The grating bars 10 may have earlike 
prolongations 33 formed in a manner to avoid deposit of the material in 
the liquid. The distance pieces 31 simply may have the form of a disk. It 
is possible to use distance pieces 31 of different height for different 
examples of application to mount devices for different purposes. 
This is not only directed as far as different devices are concerned, but 
also with respect to a grating surface one device. It is useful to 
position distance pieces 31 having a smaller width in the lower part of 
the grating surface and distance pieces 31 having a greater width in the 
upper part of the grating surface in order to have a different screening 
effect for the time of low liquid levels 6 compared with times of high 
liquid levels 7, which may occur during heavy rains. In general, this 
system of construction kit offers the possibility to simply vary the axial 
length of the grating surface 8, to adapt the device to different 
conditions, or to replace single grating bars 10 if necessary. In the same 
manner as the grating surface 8 is composed from single elements 10, 31, 
32, also the removing beam 12 is divided into single elements 34, 35, and 
36, as illustrated in the embodiment of FIG. 3. Thus, the possibility 
results simply to vary and adapt the axial length of the removing beam 12 
within this construction kit. The individual axial length of the elements 
34, 35 and 36 may be designed with respect to modular dimensions. 
It is possible also to position two units for depositing material on its 
grating surfaces 8 in conjunction with a single conveying device 17, as 
illustrated in FIGS. 4 and 5. The conveying device 17 is located in the 
middle and the removing beams 12 of the two units are rotated in opposite 
directions so that both units gather and convey the material from the 
grating surfaces in the direction to the conveying device 17. In this case 
two openings 23 or a common opening are provided in the housing 22. Here 
also the flow of the liquid in the channel 3 according arrow 30 is used in 
order to convey the material into the conveying device 17 so that the 
screw 20 can act upon the material. 
In FIGS. 6 and 7 a further embodiment of the device is illustrated having 
special advantages. The axis 2 of the grating surface 8 in form of the 
semicylinder is positioned vertically in the channel 3. The semicircular 
grating bars 10 at one end are provided with long extending prolongations 
37 so that the shape of a walking stick results. The prolongations 37 
extend in the flow direction 5 in the channel 3. The prolongations 37 form 
a connection wall 38 having a rectangular area. However, important for the 
construction is the triangular part only which is located above the 
conveying device 17 and forms a tangential transition between the 
semicircular grating bars 10 and the housing 22 of the conveying device 
17. The connection wall 38 thus generated by the prolongations 37 is a 
plane surface which may be designed open having slots, as illustrated in 
FIG. 6, but which may be designed closed also for example by a sheet 
steel. It is due to the connection wall 38 that on the one hand the unit 
having the grating surface 8 and on the other hand the conveying device 17 
may be designed as separate units and may be positioned separately in the 
channel 3. Thus, the axis 2 of the grating surface 8 is positioned 
vertically, while the axis 18 of the conveying device 17 is positioned 
slanting downwardly in different possible angles. This possibility is 
illustrated by the double headed arrow 39 in FIG. 6. Axles 32 are 
positioned in the region of the prolongations 37, while the semicircular 
grating bars 10 are free from axles 32. Here the prolongations 37 have 
openings through which the axles 32 extend. The distance of the 
prolongations and thus the width of the slots 11 between the grating bars 
10 is determined by the height of the distance pieces 31. On the other end 
of the grating bars 10 prolongations 40 may be located which are designed 
shorter than the prolongations 37. Here also axles 32 are arranged in the 
area not covered from the revolving removing elements 15. Thus, the 
semicircular grating bars 10 are positioned and held with precise distance 
to each other, especially at the line at which the removing elements 15 
enter the slots 11 so that the entry is possible without difficulty. 
During revolution of the removing elements 15 a self-adaptation occurs 
within the flexibility of the grating bars 12. The removing elements 15 
gather and push the material on the convex outside of the grating surface 
8. At the line at which the free ends of the removing elements 15 withdraw 
from the semicircular grating bars 12 the material comes free from the 
removing elements 15 and is conveyed further by the flow of the liquid and 
thus guided into the conveying device 17. The material is collected on the 
common line between the connection wall 38 and the housing 22 of the 
conveying device 17. The screw 20 is driven according arrow 41 in a 
direction in order to guide the material into the conveying device 17. 
FIG. 7 illustrates the flow of the liquid in the channel 3. In the region 
of the grating bars 10 the flow is directed perpendicular to the convex 
surface in the direction of arrows 29 through the grating surface. On the 
sidewalls of the channel inserts 42 guiding the flow of the liquid may be 
located as illustrated for one of the sidewalls. Thus, the flow direction 
of the liquid is influenced and a depositing of material is avoided in the 
corners. 
Comparing FIGS. 6 and 8 it is evident to use distance pieces 31 of 
different height. This is possible in all embodiments. Thus, screening 
devices having different width of their slots 11 may be realised, for 
example fine raking devices or raking devices with larger width of their 
slots. However, it is possible also to divide the grating surface of one 
raking device in different parts and to use distance pieces 31 of 
different width in the parts (FIG. 9) to generate an emergency overflow 
for example. 
In the embodiment illustrated in FIG. 8 the axis 2 of the grating surface 8 
is positioned slanting downwardly. The prolongations 37 of the grating 
bars 10 shown in dotted lines are formed with a buckle. The connection 
wall 38 is covered by a sheet steel 43 having a triangular shape. Thus, 
the connection wall 38 is closed. 
The embodiment of FIG. 9 is similar to the embodiment of FIG. 6. In the 
upper region of the grating surface 8 an emergency overflow is provided. 
The normal maximum liquid level 6 is shown. To facilitate loosening of the 
material from the prolongations 37 the connection wall 38 a spraying bar 
44 may be located under the liquid level to generate a flow through the 
slots between the prolongations 37 in the direction towards the conveying 
device 17. In the region above the normal maximum liquid level 6 a nozzle 
bar 45 may be arranged serving to spray service water to create a washing 
effect for the material in the conveying device 17. It is evident that the 
housing 22 is designed open in this region or the opening 23 extends into 
this area. 
While the foregoing specification and drawings disclose preferred 
embodiments of the invention, it will be understood by those skilled in 
the art that variations and modifications thereof can be made without 
departing from the spirit and scope of the invention, as set forth in the 
following claims.