Filter apparatus including filter cartridges and an inpermeable film bag

A filter apparatus is described, in which there are in the interior of a filter housing (7) a multiplicity of filter elements (1) which are suspended on the filter cover (3) and in which the inner bores of the filter cartridges are connected to the outlet nozzle (6) via a system of channels. Against the wall of the filter housing (7) there bears a film bag (2), the upper end of which is welded to an O-ring (4), which is seated in an annular groove on the flange of the filter housing, with the diameters of O-ring and film bag being identical. Furthermore, volume displacers (16, 17, 25), which extend in the axial direction over the entire length of the filter housing, are provided between filter bag (2) and inner wall of the filter housing as well as in the inner space of the filter cartridges. When a filter is changed, these volume displacers are, for example, inflated with compressed air, as a result of which the volume of residual filtrate is considerably reduced, so that less loss of dispersion occurs. The arrangement described permits an easy filter change and offers advantages in the disposal of the residues (2).

The invention relates to a filter apparatus for the filtration of liquids 
or dispersions, having a filter housing, a filter cover, having filter 
cartridges suspended from the cover, having a media-impermeable film bag, 
the length and width of which are greater than the dimension of the filter 
housing and which surrounds the filter cartridges and bears against the 
filter housing, having a feed opening arranged between cover and filter 
housing, which opening communicates with the interior of the film bag, and 
having discharge nozzles extending upward from the interior of the filter 
cartridge, which nozzles cross the filter cover and open out into a common 
discharge nozzle in the filter cover. 
Filter apparatuses of the generic type mentioned at the beginning are known 
from the prior art. For instance, in U.S. Pat. No. 3,684,100 a filter 
device is described in which there is located in the interior of the 
filter housing a flexible sleeve which can be disposed together with the 
filter cartridge and is supported on the inside of the filter element, so 
that the filter element can be quickly exchanged without contaminating the 
surroundings. In U.S. Pat. No. 4,711,717, a filter apparatus is described 
which has a media-impermeable hose which is firmly connected by its one 
end region to the one end of the filter cartridge by means of a 
disc-shaped adaptor and the second end region of the hose being closed, at 
least during the operation of the filter apparatus. In U.S. Pat. No. 
4,882,051, a filter apparatus, in particular for magnetic dispersions, is 
described, in which a likewise media-impermeable film bag is situated in a 
filter housing, the liquid to be filtered flowing in under pressure 
through its upper opening and being forced through a filter cartridge 
situated centrally in the film bag and leaving the filter apparatus 
downward, the lower end of the film bag being firmly connected to the 
filter cartridge. DE 39 09 382 and 39 17 517 disclose individual filter 
elements for magnetic dispersions which cause only a minimal loss of 
filtrate when the filter insert is changed. In the first-mentioned 
application this is brought about by there being located in an upwardly 
open annular gap between an outer supporting body and an inner supporting 
body a filter insert comprising an annular bottom part and cover part 
having inlet and outlet openings and, if appropriate, flexible walls and 
filter material between the walls, through which material the dispersion 
to be filtered is forced radially from the one hollow space into the other 
hollow space. In the last-mentioned application, a filter cartridge is 
described which is likewise flowed through radially from outside to inside 
by the dispersion to be filtered and there being contained in the inner 
space of the filter cartridge a compressible flexible volume displacer, 
which is compressed upon pressurization and thus allows the filtrate 
through and assumes its original shape again when the filter is changed, 
so that only a minimal volume is lost. 
If filter elements and filter housings in which large volumes of liquids or 
dispersions are forced through are used, increased amounts of lost 
filtrate must be expected when changing the filter cartridges on account 
of the design and combination of a plurality of filter elements to form a 
complete filter of larger filter area. If toxic, environmentally hazardous 
and expensive raw materials are used, this leads to difficulties in the 
disposal of the used filter elements or to high filtrate costs. This 
applies in particular to the filtration of magnetic dispersions in which 
polymeric binders, inorganic pigments and additives are dispersed in an 
organic solvent. Such dispersions are filtered under differential 
pressures of 2 to 10 bar through filters having pore widths of 1 to 50 
.mu.m. 
It is an object of the present invention to provide a filter apparatus of 
the generic type mentioned at the beginning which has an exchangeable 
filter insert and 
causes only a minimal loss of filtrate when the filter insert is changed 
and in which the number of parts to be cleaned is reduced 
is designed in such a way that the filter insert withstands the operating 
pressure 
when a filter is changed, any contact of the operating personnel with the 
liquid to be filtered is reduced to a minimum. 
We have found that this object is achieved by a filter apparatus for the 
filtration of liquids or dispersions, having a filter housing, a filter 
cover, having filter cartridges suspended from the cover, having a 
media-impermeable film bag, the length and width of which are greater than 
the corresponding dimension of the filter housing and which surrounds the 
filter cartridges and bears at least indirectly against the filter 
housing, having a feed nozzle provided on the cover or in the filter 
housing for the liquid, which communicates with the interior of the film 
bag and having a discharge nozzle extending outward from the interior of 
the filter cartridges, wherein the upper open end of the film bag is 
connected to an O-ring, which is seated on an annular recess of the upper 
flange of the filter housing, which is firmly connected to the cover by 
screwing, the diameter of the O-ring being equal to the diameter of the 
film bag, compressible volume displacers being arranged in the inner space 
of the filter cartridges or compressible or externally 
compressed-air-inflatable volume displacers being arranged between inner 
wall of the filter housing and the film bag or compressed air being blown 
into the space between film bag and inner wall of the filter housing 
through an opening. Further details of the invention emerge from the 
subclass, the description and the drawings.

FIG. 1 shows a design of the filter apparatus according to the invention. 
The filter element comprises a cup-shaped hollow-cylindrical outer housing 
(7) having an upper annular flange (8). Seated on the latter is the cover 
(3), which is connected to the flange by screwing and the lower part (3') 
of which is provided with various openings, which are explained in more 
detail below. A lateral opening (5) is intended for the entry of the 
dispersion into the filter vessel, into which there enter a multiplicity 
of filter cartridges (1), which are inserted and fastened (26) on the 
lower part of the cover (3'). The dispersion to be filtered flows through 
the filter cartridges in the radial direction through the filter cloth 
(27) from outside to inside and the filtered dispersion flows off through 
the inner space (12), which is connected to the openings (13) in the 
filter cover, via channels (14) and the delivery nozzle (6). Possible 
arrangements of the filter cartridges in the filter element are evident 
from the cross sectional drawings FIG. 4 and FIG. 5. 
Against the inner wall of the filter housing (7) there bears a flexible 
film bag (2), the upper end of which is open and the open end of which is 
connected to a flexible O-ring (4), the O-ring being seated in an annular 
recess (9) of the flange (8). The length and width of the film bag are 
greater than the corresponding dimension of the filter housing. In this 
way, an adequate seal is accomplished between the cover (3, 3') and the 
filter vessel (7). What is essential for the invention is that the 
diameter of the O-ring (4) is equal to the diameter of the film bag (2). 
It is namely in this way that the open end of the film bag is connected 
free from folds to the O-ring and thus provides an outstanding seal. 
When a filter change is necessary, the cover is removed by unscrewing from 
the filter housing (7) and the film bag (2) is removed and disposed of 
together with the filter cartridges and the residual dispersion located in 
the inner space of the filter. Thereupon, the filter elements (1) can be 
taken off the lower part of the cover (3'), and only the cover (3, 3') 
need be cleaned, since the inner space of the filter housing did not come 
into contact with the dispersion during the filtering time. Thereupon, a 
new filter bag can be inserted, then new filter cartridges can be fitted 
together with the cover, whereupon a further filtering cycle begins. 
A second, particularly advantageous embodiment of the filtering apparatus 
according to the invention is represented in FIG. 2. In the case of this 
design, the O-ring (4) holding the film bag (2) is not seated in the 
filter housing itself but in the recess of a separate annular part (18), 
which has two lateral grips (20). This ring (18) is additionally sealed 
from the flange (19), forming the upper end of the filter housing (7), by 
means of an O-ring (21) seated in an annular recess of the flange. On the 
ring (18) there rests an intermediate cover (3'), the construction of 
which corresponds to the lower part of the cover described in more detail 
with reference to FIG. 1. 
On the intermediate cover (3') there is the end cover (3) as a separate 
part, which is firmly connected by a screw connection to the filter 
housing (7) or the flange (19) of the latter. Inserted between the 
intermediate cover (3') and the cover (3) is a film (15), the seal being 
brought about by an O-ring (22), which is seated in an annular recess 
provided in the lower part of the cover (3) and presses the film (15) 
against the intermediate cover (3'). 
When a filter change is necessary in this filter apparatus, the screw 
connections (not shown) between cover and filter housing are loosened, the 
cover (3) is taken off, whereupon the complete filter insert with 
intermediate cover (3') can be lifted out with the aid of the grips (20) 
and removed for cleaning or disposal of the filter bag and the filter 
cartridges. In the case of this embodiment in particular, any contact of 
the operating personnel with the dispersion is avoided; in addition, the 
escape of aggressive solvents is reduced to a minimum. Finally, in the 
case of this embodiment the number of parts to be cleaned is reduced to 
the intermediate cover (3') since all other parts have not come into 
contact with the dispersion. It is also evident from the description that 
in the case of this embodiment a rapid and simple filter change is 
possible. 
A further embodiment is evident from FIG. 3. As far as the inserting and 
sealing of the upper end of the film bag (2) are concerned, this 
embodiment corresponds to the designs of FIGS. 1 and 2. However, in the 
case of this embodiment the dispersion does not enter the filter housing 
(7) laterally through the cover or intermediate cover (3, 3') but rather 
through an opening (23) which is located centrally on the lower end of the 
film bag (2). A pipe piece (11) is connected to the film bag (2) by 
welding. The pipe piece (11) of the film bag is fitted in a corresponding 
clearance (24) in the lower part of the filter housing and is provided 
with a shut-off cock (28). After flowing through the filter cartridges as 
described above, the cleaned dispersion leaves through the channels and 
cross-sections in the intermediate cover, as in the other embodiments. 
In the following it is explained how, when changing the filter apparatus 
described, the object is achieved of causing only a minimal loss of 
filtrate. Further details are revealed by FIGS. 1, 4 and 5. 
In FIG. 1 it is shown that there is a compressible body (17) in the inner 
space (12) of the filter cartridges (1). If the operating pressure is 
removed when changing the filtering apparatus, the compression body can 
expand and displaces the dispersion still remaining in the filter 
cartridges to a minimum. A further reduction in the loss of filtrate is 
brought about by air being blown in through a lateral opening (10) in the 
filter housing (7), so that, as shown in FIG. 4, the filter bag (2) is 
urged away from the wall of the filter housing (7) and is pressed 
partially into the free space between the filter cartridges (1) and in 
this way the residual volume is reduced considerably. 
In FIG. 5, an alternative embodiment for reducing the volume of residual 
filtrate is represented. In this case, air-inflatable volume displacers 
(16) are evenly distributed in the inner space of the filter housing 
between inner wall of the filter housing and film bag. Similarly, 
compressible volume displacers (25) may also be arranged at this point, as 
likewise revealed by this figure. 
The filter housing, the rings, intermediate rings and the cover preferably 
consist of stainless steel, the intermediate cover (3') may likewise 
consist of hard plastic. 
The filter cartridges contain as filter material (27) a folded, coiled or 
sintered medium known from the prior art, for example polypropylene, 
polyethylene terephthalate, polyamide, cotton, glassfibre or steel. The 
film bag (2) and the film (15) consist of synthetic plastics material, for 
example of polyethylene or polypropylene. 
The objects presented at the beginning are achieved completely by the 
embodiments mentioned above, so that cleaning costs and regenerating costs 
are saved and the losses when changing the filter are substantially 
reduced.