Note: Descriptions are shown in the official language in which they were submitted.
llZ518Z
The invention relates to an ultrafilter, more particu-
larly for filtering blood, comprising at least one slit-like
filter chamber bounded on at least one side by a membrane of a
filter element, each filter chamber communicating with an inlet
for medium to be filtered and an outlet for medium concentrated
by filtering.
A known ultrafilter of the kind in question comprises
a plurality of superposed rectangular plastic filter plates.
Each filter plate has longitudinal webs on both sides. When
two filter plates are superposed, the webs are likewise super-
posed and enclose the membrane. Grooves on which the membrane
rests are formed parallel t~ the webs, and the space between the
- 1 - ' i~
5~Z
bottom of each groove and the membrane is used for discharging
the filtrate. The slit-like filter chambers formed between the
webs and the membrane have a height (i.e. the distance from the
active portions of the membrane) of at least 150 microns.
The known ultrafilter has a disadvantage in that the
slit-like filter chambers are very long, necessitating large
pressure differences between the filter inlet and outlet. As
a result of the high inlet pressures individual components of
the ultrafilter are twisted, i.e. lose their dimensional stabil-
ity, so that the desired chamber height is no longer maintained.
Moreover, the inlet pressures may damage organic components of
the medium to be filtered. In addition, in the known ultrafilter,
a secondary filter is deposited on the membrane, so that the
filtering conditions become progressively worse during operation.
An object of the invention is to provide an ultra-
filter of the initially-mentioned kind which gives efficient
filtering, with constant output over a long time, even when the
uniform f~ilter chamber heights are extremely small, using reason-
able pressure differences between the filter inlet and outlet.
To this end, the invention provides a device for ultra-
filteration, especially for the filtration of blood, comprising:
a housing having spaced first and second walls, and having
an inlet for medium to be filtered, an outlet for concentrated
medium, and an outlet for filtrate;
means within said housing defining at least one gap-shaped
chamber, in the form of a plurality of flow channels during use,
for medium being filtered; and an adjacent chamber for filtrate,
~l'Z5~Z
said chambers being separated by a membrane, said outlet for
filtrate communicating with said chamber for filtrate, and
said inlet for medium -to be filtered and said outlet for concen-
trated medium both being in communication with said gap-shaped
chamber for medium being filtered;
said chamber for filtrate containing a substantially non-
compressible, dimensionally stable substrate layer having a
structure comprising a plurality of protuberances extending
against said membrane, said protuberances having spaces of 0 -
2.5 mm therebetween and a thickness of 0.1 - 0.5 mm, said mem-
brane and said substrate layer being formed as a filter element
unit; and
the height of each gap-shaped chamber for medium being
filtered being between 8 and 150 microns.
Advantageously, the substrate layer comprises a fabric
having a clear mesh width between 0 and 2.5 mm and a thickness
between 0.1 and 0.5 mm.
From another aspect, the invention provides an ultra-
filter comprising:
a housing having first and second parallel walls, an inlet
for a medium to be filtered and an outlet for concentrated med-
ium; and
a plurality of filter element units disposed in said hous-
ing between said first and second parallel walls to define a
plurality of slit-like filter chambers each of height between
about 8 and 150 microns communicating with said housing inlet
-- 3 --
~lZ51~2
and outlet and each being in the form of a plurality of flow
channels during use;
each of said filter element units comprising a substrate
layer and a membrane with said membrane bounding a slit-like
filter chamber, said subs-trate layer being made of a substan-
tially non-compressible, dimensionally stable material and having
a structure comprising a plurality of protuberances, said pro-
tuberances having spaces therebetween of 0 - 2.5 mm and a height
of 0.1 - 0.5 mm.
The thus-constructed ultrafilter has the advantage of
being very easy to manufac~ure, since the membrane support of
substrate layer can be a plastics fabric or a thin foil embossed
in the appropriate shape. The gap-shaped filter chamber height
is obtained when the membrane assumes the surface structure of
the substrate layer, either as a result of excess pressure on
the filter or negative pressure under the filter. A number of
uniform flow channels form as a result. The resulting chamber
height can be very small, e.g. between 8 and 150 microns. The
filter has been found extremely efficient during a long-term
test.
Advantageously, the clear mesh width of the fabric is
between 0.5 and 2 mm and theaverage fiber thickness is between
0.2 and 0.3 mm; in the case of fabrics made of plastics fibers,
the fiber thickness is equivalent to the average fiber diameter.
The filter comprises a housing having first and second
parallel walls between which each filter element unit is dis-
posed.
~" 9 - 4 -
5182
In apreferred embodiment of the filter, a filtrate dis-
charge element, made of a material permeable to the filtrate, is
accommodated in a recess in the substrate layer of each filter
element. The last-mentioned device is particularly advantageous
when the ultrafilter has a number of filter chambers defined
by a plurality of filter elements disposed in the housing. This
structure produces a number of points of contact which exactly
define the extremely constant chamber height.
In an ultrafilter of the aforementioned kind there may
be two filter elements respectively disposed adjacent to the walls
of the housing, the remaining filter element units being covered
on all sides by membranes.
In the last-mentioned device, filtrate discharge ele-
ments of the filter element units are perferably juxtaposed and
pressed against one another in sealing-tight manner and aligned
with the filter outlet.
When the substrate later is composed of fabric, the
thickness of the filtrate discharge elements is dependent of the
thickness of the fibers of the fabric.
In the thickness direction, the filtrate discharge
element may extend in sealing-tight manner through the membrane
or membranes.
Alternatively, each filtrate discharge element may have
a flow aperture therethrough and be covered in sealing-tight
manner, except for the flow aperture, by the filter medium, the
flow apertures being aligned with one another and with the filtrate
51~2
outlet. The aligned apertures make it easy to inset a rod when
assembling the filter element units r which can thus be aligned
in the desired manner.
In one embodiment, the filter element units are circular
and have a central inlet for the medium to be filtered. The out-
lets for the filtrate and concentrated medium are provided in the
peripheral region.
The resilient, porous, disc-shaped filtrate discharge
elements press the filter element units together in sealing-tight
manner, so that the medium (e.g. blood) to be filtered cannot
enter the filtrate duct. The filtrate can flow through the por-
ous seal into the duct.
In another embodiment, the filter element units are
rectangular, the inlet for the medium to be filtered being
provided near one edge and the outlet for the concentrated medium
being provided near the opposite edge.
The untrafilter having a number of filter element
units is very cheap to manufacture, and can therefore form a
typical throwaway unit. The device is very simple to assemble.
Two housing parts are provided with corresponding connections,
and the end filter elements (i.e. the filter element units in
which a fabric-like surface structure is embossed on the inside
of the parallel housing walls or covered by a corresponding
fabric) are disposed at the opposite major inner walls of two
housing halves. The filter element units which are mass-produced
in completely automatic manner, are placed in the correct position
in the form of a stack, using centring pins, and inserted in
the housing. Next, the housing halves are welded together under
-- 6
~5~2
a pressure such that the filtrate discharge elements abut in
sealing-tight manner and the desired or rated filter chamber
height is obtained during operation.
Further objects and advantages of the invention will
appear from the following description of perferred embodiments,
given with reference to the appended drawings, in which : -
FIGURE 1 diagrammatically shows a first embodiment ofan untrafilter according to the invention;
FIGURE 2 shows a detail II from Figure l;
FIGURE 3 is a longitudinal section through a second
embodiment of the ultrafilter;
FIGURE 4, which appear on the third page of drawings,
shows a filter element unit from the ultrafilter of Figure 3;
FIGURE 5, which appear on the second page of drawings,
is a partical plan view of the untrafilter of Figure 3;
FIGURE 6 is a longitudinal section through a third
embodiment of the ultrafilter;
FIGURE 7 shows a filter element unit from the ultra-
filter of Figure 6; and
FIGURE 8 is a plan view of the ultrafilter of Figure 6.
Figure 1 shows a first ultrafilter embodying the
invention and comprising a housing having a first chamber wall
4 and a second, parallel chamber wall 5 spaced from wall 4.
Walls 4 and 5 are circular and are interconnected by an edge 11.
At the centre of the first wall 4 there is aninle~ 1 for the med-
ium to be filtered. In the neighbourhood of edge 11, wall 4 has
1l32
an outlet 2 for filtrate. An outlet 3 for the concentrated
medium is provided at the diametrically opposite place on edge
11. A substrate layer is provided on the inner surface of wall
4 in the form of a fabric 6 (as shown) or by embossing the inner
surface of wall 4 to produce a structure having a number of
protuberances. Fabric 6 is apertured near inlet 1. On its
surface remote from wall 4, fabric 6 is closed in sealing-tight
manner by a membrane 7 of aknown kind used in ultrafilters.
A filtrate discharge element 8 (see Figure 3) made of
a material permeable to the filtrate is disposed in a recess in
fabric 6 below outlet 2
As shown by the detail in Figure 2, interconnected
free spaces 9 are left between fibers 10 of fabric 6 even if,
at the operating pressure, the membrane 7 penetrates somewhat
into the f~ee spaces. In this manner the filter chamber heights
are obtained. Housing wall 4 touches the fabric 6 through
the membrane 7 at the points where the fibers cross. Consequently,
the chamber height depends on the dimensions of the fabric,
and is between 8 and 150 microns. The medium supplied to the
central inlet 1 is distributed and flows radially outwards
through slit-like filter chamber 20, as shown by the arrows,
to annular duct 15, where the concentrated medium is collected
and discharged through outlet 3. The filtrate
flowing through membrane 7 flows along the inter-connected
free spaces 9 of fabric 6 through the porous filtrate dis-
charge element 8 to the filtrate outlet 2.
.. ~,
~ - 8
~5~2
In the second embodiment, shown in Figures 3 to 5,
there are two end filter el.ement units 12 instead if the single
filter element unit 12 shown in Figure 1. One filter element
unit 12 is disposed adjacent to wall 4 and the other to wall 5.
Between the filter medium sides of filter element units 12,
there are two additional filter element units 12a covered on
both sides by membrane 7 welded in sealing-tight manner at an
inner and an outer edge 14. The annular fabrics 6 have recesses
containing filtrate discharge elements 8 which, with the exception
of a flow aperture 13, are covered at the ends by membrane
7. Apertures 13 are aligned with one another and terminate in
outlet 2.
The medium to be filtered, which is supplied through
the c~entral inlet 1, flows from the central cavity into filter
chambers 20, where it flows radially outwards and is concentrated,
and then collected in annular duct 15 and discharged through
outlet 3. The filtrate travelling through the membrane 7 flows
through the free spaces in the fabric to the filtrate discharge
elements 8, through which the filtrate passes and is discharged
via apertures 13 and outlet 2.
The embodiment shown in Figures 6 to 8 is rectangular
and elongated, in contrast to the embodiment in Figures 3 to 5.
The inlet 1 for the medium to be filtered is disposed in the
neighbourhood of one end of the filter, whereas the outlet 3
for the concentrated medium is in the neighbourbood of the other
end. Outlet 2 is in the neighbourhood of inlet 1. The other
~"51~32
details of the devices are similar to those of Figures 3 to 5.
The filter chamber is uniform as a result of the
many points of contact between the membrane and fabric, which
are spaced in accordance with the points of intersection between
the fibers of the fabric.
The chambers are produced by the membrane, which
bends under excess or negative pressure. Seals are used only
for discharging the filtrate; in addition, since they are
resilient, they seal the filter chambers against the filtrate
outlet.
EXAMPLE
The untrafilter of Figure 3 was used to filter hepar-
inised bovine blood. The overflow capacity was 300 ml/min.
The fabric used had a fiber thickness of 0.28 mm. The inner
mesh width varied, i.e. was 1.4, 1.0 and 0.63 mm. The filtrate
capacity was 27, 50 and 75 ml/min when the differential pressure
between the inlet and outlet was 0.17, 0.22 and 0.25 bar
respectively.
Further tests showed that, in the case of bovine
blood, the filter was efficient up to a concentration of 40%.
-- 10 ~
