Filter device

The filter device has a housing with elongated top and bottom walls and side walls which taper inwardly from top to bottom. The top wall has extending downwardly therefrom into the housing a generally flat filter membrane support with a quadrangular periphery, a pair of filter membranes being disposed on opposite sides of the support and sealingly bonded to its periphery, the support having a center portion with spaced coplanar surfaces on each side to provide support for the center portion of the filter membranes. The housing is provided with an opening communicating with the space between the two filter membranes and with an opening communicating with the space between the housing and the two membranes. The bottom wall and side walls of the housing are in the form of a unitary molding of organic polymeric material open at its upper end, and the top wall and the downwardly extending filter membrane support is formed of another molding of organic polymeric material bonded about the periphery of the top wall into the open end of the outer molding. Because of such structure the device can be manufactured at relatively low cost and is compact while yet affording a large filtering area.

TECHNICAL FIELD 
This invention relates to a filter device of the type incorporating two 
filter membranes of equal surface area bonded to the oppositely disposed 
sides of a support member disposed within a housing, the housing having 
one fluid opening which communicates with the space between the two filter 
membranes and another opening which communicates with the space between 
the housing and the assembly of the two membranes and the support. 
BACKGROUND ART 
Filter devices of a general type incorporating two filter membranes of 
equal size on oppositely disposed sides of a membrane support are well 
known in the art as shown, for example, by U.S. Pat. No. 3,730,353. The 
purpose of using the two filter membranes, instead of only one, is to 
double the available filtration area without commensurate increase in the 
size of the filtration device. However, such filter devices have 
heretofore consisted of assemblies of three or more components, in 
addition to the two filter membranes, and at that with the geometry of the 
components and assemblies being such as to involve difficulties and 
expense in manufacture without compensating increase in filtration 
performance or effective filter life. 
The objective realized by the present invention is a compact filter device 
which provides the desired increased filtration surface area by the 
incorporation of two membranes and which can be manufactured at relatively 
low cost using, in addition to the two membranes, only two components, 
each a plastic molding, which can be readily bonded together. 
DISCLOSURE OF INVENTION 
The filter device of the present invention comprises a housing having 
elongated top and bottom walls and side walls which taper inwardly from 
top to bottom. In the preferred embodiment each of the top and bottom 
walls is of generally rectangular shape with a length more than four times 
its width and all of the side walls, four in number, are generally 
trapezoidal shaped, two opposed side walls being relatively narrow and the 
other two opposed side walls being flat and relatively wide whereby the 
housing is of a generally flat shape but with all of the side walls 
tapering from top to bottom thereof. 
The top wall has extending downwardly therefrom into the housing a 
generally flat filter membrane support with a quadrangular periphery which 
is spaced from the bottom wall and from the side walls, the pair of filter 
membranes being sealingly bonded to the periphery of the support, one on 
each side thereof, the support having a center portion with a plurality of 
spaced coplanar surfaces on each of the two sides thereof adjacent the two 
filter membranes thereby to provide support for the center portions of the 
filter membranes. In the preferred embodiment the coplanar surfaces on 
each side of the support center portion are in the form of elongated ribs 
on a thin plate which connects to the periphery of the support, the ribs 
extending in a direction from top to bottom of the support. 
The housing is provided with an opening which communicates with the space 
between the housing and the assembly of the two membranes and the membrane 
support, and an opening through the top wall and through the periphery of 
the support which communicates with the space between the two filter 
membranes. In the preferred embodiment the thin plate with the ribs 
thereon which forms the center portion of the support has an upper end 
which is spaced from the portion of the support periphery through which 
the top wall opening extends thereby forming a header which provides 
communication between the opening and the spaces between the elongated 
ribs on the thin plate. 
Further and in accordance with the preferred embodiment of the invention, 
the bottom wall and all of the side walls of the housing are in the form 
of a unitary molding of organic polymeric material, such molding being 
open at its upper end, and the top wall with its downwardly extending 
filter membrane support is formed by a second molding of organic polymeric 
material, this second molding being sealingly bonded about the periphery 
of the top wall into the opening at the upper end of the other plastic 
molding after the filter membranes have been bonded to the filter membrane 
support. Hence, other than the two filter membranes, only two components, 
each a relatively inexpensive plastic molding, are required. Particularly 
by reason of the tapered shape of the molding which provides the bottom 
and side walls of the housing, it can be molded with relatively little 
trouble and expense. Still further, in the preferred embodiment the top 
wall is provided with an additional fluid opening or openings which 
communicate with the space between the housing and the assembly of the 
filter membranes and the filter membrane support. The tapered shape of the 
housing provides sufficient spacing between the housing side walls and the 
assembly, at the top of the housing, to permit such additional openings at 
that location without there being wasted space in other portions of the 
device. These and other features and advantages of the invention will be 
more apparent from the detailed description of the preferred embodiment 
which follows hereinafter.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawings, the preferred embodiment shown comprises a 
housing 2 having an elongated, rectangular-shaped top wall 4 the length of 
which is more than four times the width, an elongated, rectangular-shaped 
bottom wall 6 also having a length more than four times its width, the 
length and width of the bottom wall being less than the length and width, 
respectively, of the top wall. The housing has a pair of opposed side 
walls, 8 10, which are of trapezoidal shape and relatively narrow, and a 
pair of opposed side walls, 11 and 12, which are also of trapezoidal shape 
and which are flat and relatively wide, all of these side walls connecting 
to each other and to the top and bottom walls whereby the housing has a 
substantially flat shape but tapered from top to bottom on all sides 
thereof. 
The top wall 4 has extending downwardly therefrom into the housing a filter 
membrane support 14 which is spaced from the bottom wall and the side 
walls of the housing. This support has a quadrangular peripheral portion 
16 each of the oppositely disposed lateral sides of which is a continuous 
planar surface, one of these continuous planar surfaces being shown at 18 
and the other being shown at 20 (see FIG. 3). The center portion of the 
filter membrane support has a plurality of surfaces 22 on one side thereof 
which are coplanar with each other and, on the other side thereof, another 
plurality of surfaces 24 which are coplanar with each other. 
A filter membrane 26 is bonded about its periphery to the continuous planar 
surface 18 of the peripheral portion of the support, the center portion of 
the filter membrane 26 being supported, during use of the device, by the 
coplanar surfaces 22. A second filter membrane 28, which is identical in 
shape to the filter membrane 26, is bonded about its periphery to the 
continuous planar surface 20 of the periphery of the support, the center 
portion of the filter membrane 28 being supported, during use of the 
device, by the coplanar surfaces 24. The top wall 4 has a fluid opening 38 
which extends therethrough and through the peripheral portion 16 of the 
support and hence into communication with the space between the filter 
membranes. The coplanar surfaces 22 are spaced from each other, and 
likewise the coplanar surfaces 24 are spaced from each other, so as to 
allow fluidflow therebetween and hence between and in contact with the 
filter membranes. In the preferred embodiment shown the peripheral portion 
16 of the support is rectangular and the surfaces 22 are provided by a 
plurality of equally spaced, elongated ribs 30 which extend in a direction 
from top to bottom of the support and which are formed on a thin plate 32 
which connects to the bottom and sides of the peripheral portion 16 of the 
support, the surfaces 24 being provided by a like plurality of elongated 
ribs 34 likewise extending in a direction from top to bottom of the 
support and formed on the other side of the thin plate 32. The plate 32, 
with the ribs 30 and 34 formed thereon has an upper end 36 which is spaced 
from the portion of the periphery 16 through which the opening 38 extends, 
thereby providing a header between the opening 38 and the spaces between 
the ribs 30 and between the ribs 34 thereby to provide fluid flow between 
the filter membranes and to or from the opening 38. 
The housing must be provided with at least one opening for fluid flow into, 
or from, the space between the housing and the assembly of the two filter 
membranes and the filter membrane support and, in the preferred embodiment 
shown, the housing is provided with two such openings, opening 42 which is 
through the bottom wall 6 and opening 44 which is through the top wall 4 
at the side thereof adjacent the wall 8. The provision of the two openings 
42 and 44 enables the fluid inlet and fluid outlet connections both to be 
made at the top of the device, by using openings 38 and 44, or with one 
connection being made at the top and the other connection being made at 
the bottom of the device by using openings 38 and 42. Whichever of opening 
42 and 44 is not used can be plugged. All of the openings 38, 42 and 44 
are provided with a stepped cone exterior surface, as shown at 48, for 
ease in the securement of elastomeric tubing. Additionally, the housing of 
the preferred embodiment shown is provided with an opening 50 through its 
bottom wall and an opening 52 through its top wall, each of which openings 
communicates with the space between the housing and the assembly of the 
filter membranes and the filter membrane support. These openings 50 and 52 
are to enable the escape of air or other gas while the device is in use 
for filtering a liquid, the opening in use for this purpose being provided 
with a hydrophobic filter, not shown, and the other of the openings, not 
in use, being plugged. The choice of the opening 50 or 52 to be used for 
the escape of air or other gas, if such escape is desired, depends on the 
orientation of the device during use, the escape opening for the air or 
other gas always being positioned on top of the device in its orientation 
as used. 
In use, the liquid to be filtered flows into the housing through either 
opening 42 or 44, through the filter membranes into the space therebetween 
and then out through opening 38. The coplanar surfaces on each side of the 
support in the center portion thereof support the filter membranes and 
maintain the spacing therebetween. 
In this preferred embodiment, the bottom wall 6 and all of the side walls 8 
and 10 and 11 and 12 of the housing are in the form of a unitary molding 
of organic polymeric material, such molding being open at its upper end as 
shown in FIG. 1. The top wall 4 with its downwardly extending filter 
membrane support 14 is formed by a second unitary molding of organic 
polymeric material, again as best seen in FIG. 1, the top wall being 
bonded and sealed about its periphery into the upper open end of the other 
molding. The open upper end of the molding which forms the bottom and side 
walls of the housing is preferably formed with a continuous groove 58 
around its periphery for reception of the periphery of the top wall 6. The 
top wall 6 is, of course, bonded to the open upper end only after the 
membranes are sealingly bonded to the support. 
Hence, the structure enables manufacture of the device using, in addition 
to the two filter membranes, only two components, each a unitary plastic 
molding, which can be readily bonded together in sealed relationship. 
Where the organic polymer used is thermoplastic, as is preferred, heat 
bonding and sealing can be used, just as for bonding and sealing the 
filter membranes to the support--though bonding and sealing with an 
adhesive can be used if desired. 
In the particular embodiment shown the actual dimensions of the support, 
within its peripheral portion are: length about 12.5 cm., width about 8 
cm. This provides about 200 sq. cm. of filtering area, the external 
dimensions, i.e. of the housing exclusive of the tube fittings, being: 
length about 14.5 cm., width at center about 10.5 cm., thickness at center 
about 1.5 cm. Hence the device is compact while yet providing a large 
filtering area. 
The filter membrane used can be as desired though for most uses of the 
device the requirement is for microporous membrane and it is preferred 
that the membrane be of organic polymer particularly for ease in sealing 
and bonding. The organic polymer used for the moldings should preferably 
be a thermoplastic, polypropylene being typical. 
It will be understood that while the invention has been described 
specifically by reference to a preferred embodiment thereof various 
changes and modifications can be made all within the full and intended 
scope of the claims which follow.