GB2132913A - Fluid filter - Google Patents

Abstract

A filter for water filtration, particularly for the depyrogenisation and/or sterilisation of infusion solutions, com- prises a selectively permeable flat membrane which suitably has a cut-off of at least 5000 daltons and a pore size at most equal to 0.2 micrometres and which is supported at both sides by a planar support fleece or cardboard and folded together with these supports to form a pleated filter unit (17). A parallelepipedonal housing (1,2) with at least one inlet (4) and a vent at a filling side and an outlet (6) at a pure side encloses the filter unit (17) at all sides. The housing (1,2) is of asymmetrical cross-section in that a fluid distribution space (18) is formed along the filter unit fold edges on the filling side and the fold edges on the pure side lie against the facing housing wall surface. <IMAGE>

Description

SPECIFICATION Fluid filter The present invention relates to a fluid filter, especially a filter for water filtration, particularly for depyrogenisation and/or sterilisation of an infusion solution.

To increase the filter area, it is known to fold a flat filter blank and a support thereof into a plurality of pleats so that a pleated unit having a large effective filter area is formed. The filter unit can be parallelepipedonal and arranged in an enclosing housing (DE-OS 31 43 542), be a hollow cylinder arranged in a corresponding housing (DE-OS 31 28 546), or be a hollow cylindrical segment arranged in an appropriately adapted housing (DE-OS 30 07 065). Such filters are constructed either as overflow filters or as throughfl ow filters.

A filter for the above-mentioned purpose should desirably have a large effective filter area with relatively small housing dimensions and should be constructed to permit a uniform distribution of the fluid over the entire effective filter area at a filling side and relatively high pressures on the filter surfaces and housing surfaces. Moreover, the filter should be relatively economic to produce. In these respects there is scope for optimising the aforementioned prior art filters, which are designed for the special treatment of blood or for the general treatment of fluids.

According to the present invention there is provided a fluid filter comprising a pleated filter unit which comprises a selectively permeable membrane supported at each face thereof by a respective fluid-permeable support sheet and which is enclosed by a substantially parallelepipedonal housing formed from two interconnected shell halves conjoining in a plane generally parallel to the planes of the filter unit pleats, the housing being provided with an inlet duct and a vent duct extending transversely to said plane and over the depth of the filter unit at an inlet side portion thereof and with an outlet duct extending transversely to said plane and over the depth of the filter unit at an outlet side portion thereof, the fold edges of the filter unit at at least the outlet side portion thereof being in contact with the respectively facing internal wall surface of the housing, and sealing material being disposed between the filter unit and the housing internal wall surfaces other than those surfaces facing the inlet and outlet side portions of the unit.

In a preferred embodiment there is provided a filter for water filtration, particularly for the depyrogenisation and/or sterilisation of an infusion solution, comprising a selectively permeable, flat membrane with a cut-off #- 5000 daltons and a pore size ~ 0.2 micrometres, the membrane being supported at both sides by a planar support fleece or cardboard, which conduct liquid threedimensionally therethrough and do not give off fibres, and being folded together with this support into a pleated filter unit. A parallelepipedonal housing with at least one inlet and one vent on a filling side and an outlet on a pure side encloses the filter unit at all sides.The cross-section of the housing is such that, in the case of use as a throughflow filter, a fluid distribution space is formed along the fold edges on the filling side and the fold edges on the pure side rest against the facing housing wall surface, and in the case of use as an overflow filter, the fold edges rest against both facing housing wall surfaces. Distributor passages bulging out at the housing and extending over the depth of the filter unit are provided in the region of the inlets and outlets. The housing in the region of its end faces has free spaces which enlargingly enclose the end faces of the filter unit and cover both the end pleats of the unit, which extend in direction of the end faces of the unit, wherein these spaces are filled by a sealing material through several passages in the housing.The housing itself is formed from two shell halves, wherein the dividing plane thereof extends parallelly to the plane of stratification of the membrane pleats and transversely to the longitudinal axis of the distributor passages and the two shell halves are durably connected together in this dividing plane, for example by way of gluable or weldable connecting flanges of the shell halves in the dividing plane and snap fasteners at each end face of the housing.

An embodiment of the present invention will now be more particularly described with reference to the accompanying drawings, in which: Figure 1 is a schematic cross-section, on the line 1-1 of Fig. 2, of a filter embodying the invention; Figure 2 is a plan view of a lower shell of a housing of the filters; Figure 3 is a partial longitudinal section along the line 3-3 of Fig. 2; and Figure 4 is a schematic cross-section, to an enlarged scale, on the line 4-4 of Fig. 2.

Referring now to the drawings, there is shown a filter comprising a pleated filter unit 17 enclosed in a housing. The filter unit comprises a selectively permeable membrane 14 with a microporous membrane structure, for example on a cellulose base, the membrane having a cut-off of at least 5000 daltons and a pore size not exceeding 0.2 micrometres and being supported at both sides by planar support fleeces or cardboard sheets 15 and 16, which are fibrous but which do not give off fibres. The membrane and support are folded together to form the pleated unit 17. For a membrane width of 220 millimetres, pleat width of 14 millimetres and a pleat or fold number of 35, an effective filter area of 0.2 square metres is formed.The filter unit 17 is so sealed by sealing material 8 in the housing 1 and 2 that the fluid can flow only from the filling side through the first support fleece 16, through the membrane 14 and the second support fleece 15 to the pure side.

The housing consists of two half shells 1 and 2 with sealing flanges 13 and 11 which extend in the plane of stratification and are glued or ultrasonically welded to each other.

As is evident from Figure 2, the housing is provided on the filling side with an inlet 4, which, at right angles to the fold edges of the unit 17, passes over into a distributor shaft 4',4", and also with a vent or outlet 5, which passes over into a corres ponding distributor shaft 5',5" at the other end of the housing. On the pure side, the housing has an outlet 6, which correspondingly passes over into a distributor shaft 6',6".

As is apparent from the sectional view of Fig. 1, the housing is of asymmetrical cross-section, in particular with respect to the fold edges pointing towards the filling side and the fold edges pointing to the pure side. On the filling or pressure side, the housing enlarges in the region of the fold edges into a a fluid distribution space 18, whilst the fold edges on the pure side bear directly against the facing housing wall. In this manner, a good fluid distribution on the filling side is achieved and a firm support of the fold edges against the housing is provided on the side of the pressure gradient. This embodiment is particularly suitable as a throughflow filter. In the case of use as an overflow filter, the connection 5 is used as an outletforthe medium on the filling side and as a throttle location for pressure build-up.For the avoidance of short-circuit paths, the fluid distribution space 18 is dispensed with and the fold edges lie against the facing housing wall.

As is evident from Fig. 2, the housing widens in the region of the ends of the unit 17 so that free spaces 9 are formed, which serve for the reception of a sealing material 8 partially sealing the side edges and completely sealing the end surfaces of the unit 17. Similarly, free spaces 3 are provided in the longitudinal direction of the two shells 1 and 2, which free spaces face the end pleats 17' of the unit 17 and also serve for the reception of the sealing material 8. The material 8, which is pressed through 7 in the shells 1 and 2 into the free spaces 3 and 9, preferably consists of a physiologically harmless, permanently resilient material, for example silicone or polyurethane.

As is evident from Fig. 4, the sealing material 8 is preferably arranged on the side of the pressure gradient, i.e. the fluid pressed from the filling side into the open folds presses the end pleat 17' on the pure side against the preferably permanently resilient sealing material 8 so that apart from an adhesion seal also a pressure seal is formed. The space 18, which is triangular in cross-section, is sealed against the sealing material 8 by a respective additional sealing rib 10 at each of the housing end faces.

As is evident from Figs. 2 and 3, two snap fasteners 12 and 13 are arranged as assembly aids at both housing end faces and are formed by a hook 12 of the shell 2 engaging over the flange 13 of the shell 1.

The construction of the housing is extremely simple. The ready pleated unit 17 is laid, according to Fig. 2, into the lower shell 2 and covered by the upper shell 1, for which the snap fasteners 13 and 12 at the housing end faces form an assembly connection. Subsequently, ultrasonic welding of the flanges 11 and 13 is effected and the free spaces 3 and 9 are injected with the sealing material 8.

In order to prevent the flowable and rigidifying sealing material 8 introduced into the free spaces 3 from penetrating into the distributor shafts, which are open towards the filter unit, and reducing their cross-section, low step barriers 19, extending para llei to the folding, are arranged at both ends of the free opening of the distributor shafts, or the free opening of the distributor shafts begins closely underneath the free spaces 3 and ends closely above the free spaces 3.

With a relatively large filter area and a small housing dimension, the production of the individual parts, their assembly and the manipulation of the entire filter is relatively simple.

Claims (13)

1. A fluid filter comprising a pleated filter unit which comprises a selectively permeable membrane supported at each face thereof by a respective fluid-permeable support sheet and which is enclosed by a substantially parallelepidedonal housing formed from two interconnected shell halves conjoining in a plane generally parallel to the planes of the filter unit pleats, the housing being provided with an inlet duct and a vent duct extending transversely to said plane and over the depth of the filter unit at an inlet side portion thereof and with an outlet duct extending transversely to said plane and over the depth of the filter unit at an outlet side portion thereof, the fold edges of the filter unit at at least the outlet side portion thereof being in contact with the respectively facing internal wall surface of the housing, and sealing material being disposed between the filter unit and the housing internal wall surfaces other than those surfaces facing the inlet and outlet side portions of the unit.

2. A filter as claimed in claim 1, wherein the membrane has a cut-off of at least 5000 daltons and a pore size of at most 0.2 micrometres.

3. Afilter as claimed in either claim 1 or claim 2, wherein each of the support sheets comprises fibrous material.

4. A filter as claimed in any one of the preceding claims, wherein each of the ducts comprises a distributor passage formed in an outwardly projecting portion of the housing.

5. A filter as claimed in any one of the preceding claims, wherein the housing is provided with openings as introduction inlets for the sealing material in flowable state.

6. A filter as claimed in any one of the preceding claims, wherein the housing shell halves are provided with flanges bonded together in said plane.

7. A filter is claimed in any one of the preceding claims, wherein the housing is provided at each of two oposite ends thereof with a snap fastener connecting the shell halves together.

8. A filter as claimed in claim 7, wherein the housing is made of plastics material and the ducts and the fasteners are formed integrally with the shell halves.

9. A filter as claimed in any one of the preceding claims, wherein the fold edges of the filter unit at the filling side portion thereof are disposed at a spacing from the respectively facing internal wall surface of the housing.

10. A filter as claimed in claim 9, wherein the space between the fold edges at the filling side portion of the filter unit and the respectively facing internal wall surface has the cross-sectional shape of a substantially equilateral triangle, the hypoteneuse of which extends over the depth of the filter unit.

11. A filter as claimed in any one of the preceding claims, wherein the filtr unit is so arranged in the housing that the free edges of both end pleats of the unit are disposed at the filling side portion thereof, the sealing material being resilient and being disposed to provide a seal between the housing and the end pleats at the outlet side portion of the unit.

12. A filter as claimed in any one of the preceding claims, wherein the housing is provided at each end of each duct with barrier means disposed to prevent ingress of the sealing material into that duct.

13. A filter substantially as hereinbefore de- scribed with reference to the accompanying drawings.