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Description  |
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BACKGROUND TO THE INVENTION
The invention is concerned with apparatus for filtration of fluids and of
carrying out chemical or biochemical analyses requiring prior filtration
of fluids.
In one of the commonest laboratory techniques a suspension of solid
particles in liquid is separated out by filtration. In its simplest form
the filtration is brought about by folding a disk of filter paper into a
cone, fitting the cone into a rigid conical filter funnel and inserting
this in a flask which is the receiver for the filtrate. More complex
apparatus may require elaborately constructed filter means, filter
supports, vacuum or pressure pumps and valves. After filtration is
complete the apparatus is normally readied for re-use by disassembling it
and washing or sterilizing the individual parts. The storage or bench
space required for adequate numbers of apparatus and the labour required
to assemble and wash them can be considerable. Other disadvantages of this
common technique are that the apparatus (being often made of glass) is
easily broken, it can be knocked over easily, and unless special fume
hoods are available volatile solvents may give off flammable or toxic
fumes. Labeling on filters or receivers must be carefully removed in order
to avoid confusion when the apparatus is re-used. When biological
materials are handled inconvenient precautions are needed to prevent
airborne microorganisms contaminating the material being filtered.
A frequent hazard experienced by travellers, campers and survivors of
earthquakes etc, is the presence of pathogenic microorganisms in the
drinking water. These organisms can be removed by filtration. However, it
is rarely practicable to carry or store a bulky filtration apparatus. Many
instances of illness ensuing from the drinking of contaminated water might
be avoided if a lightweight and portable filtration apparatus were
available. Occupants of lifeboats to whom only salt water is available
would similarly benefit if a lightweight, portable desalination apparatus
were available.
A related problem occurs in many procedures for chemical or biological
analysis, where it is necessary to filter the fluid sample before adding
the test reagents. For example, it may be difficult to measure the acidity
of a soil suspension or lake water by means of a colour sensitive
indicator unless the sample is first clarified. In addition to the labour
required to perform the filtration, labour is also required to make up
solutions of the test reagents and dispense them.
I have realized that the weight and the space normally taken up by the
components of filter assemblies, the work involved in fitting them
together and of cleaning them, and the making up and adding of chemical
reagents are major problems to be overcome in many types of filtration
work and in providing local supplies of potable water. It is important to
the appreciation of my invention to understand that a complete filtration
apparatus comprises three functional elements, namely, the filter means
itself, and receptacles for both the fluid to be filtered and the filtered
fluid (functionally equivalent to the aforementioned funnel and receiver),
said receptacles being capable of holding the whole volume of fluid until
such time as it is put to further use. Many inventions claimed to be
filtration apparati are not, in fact, complete.
Accordingly, my invention provides a lighweight and self-contained
preformed filtration apparatus of insignificant volume when not being
used, comprising a filtration means such as a paper or cloth or membrane
filter, and two sheets of flexible film or one sheet of said film folded
double, said components being joined together in such a way that
compartments functionally equivalent to the aforementioned funnel or
receiver are formed from the film but are connected to one another
internally by said filter means.
My invention also provides for said receiver to be formed in such a way
that an orifice is available either directly or only after cutting off a
piece of the film, or else it contains a drinking tube or straw through
which the filtered fluid may be sucked without need to tilt the apparatus.
In each of these cases filtrate may be removed without need to first
remove the remainder of the suspension being filtered.
My invention also provides for a filtration apparatus in which the fluid
may be isolated from aerial contamination by simply folding the flexible
top, and which, when in use, may be suspended from its upper end by means
of hooks, wires or other suspending means, so that it may conveniently be
suspended from a wall-rack at the side of the work area, rather than
standing on a bench.
My invention also provides for indicators of various chemical or
biochemical properties (for example, pH, Redox value, etc) to be sealed
into one or more of the compartments if so desired, so that tests for
these properties can be made automatically on the suspension or filtrate.
My invention also provides for a plurality of filtration compartments to be
formed together, with successive filter means of different porosities and
with different chemical or biochemical test reagents sealed in or between
each receiver, so that a liquid poured into the funnel undergoes
successive chemical reactions as it passes through the compartments.
Such apparatus for filtration or chemical analysis being made of flexible
material can be stored flat in large numbers in a small space, either
lying on top of one another, or removably attached to one another as, for
example, on a continuous roll from which single units may be removed by
tearing along a perforation. Thus it considerably alleviates the bulk and
storage problems associated with carrying out large numbers of
filtrations. It is important to note that while the funnel and receiver in
my apparatus have no internal volume until the apparatus is put into use,
these elements are each and individually capable of holding the whole
volume of fluid which is to be filtered, and that being flexible they
dilate or contract as necessary to accomodate the addition of fluid to the
apparatus and the movement of fluid through it as it passes through the
filter means under the influence of gravity.
To use the apparatus the funnel compartment is held open, for example, by
thumb and forefinger and the fluid to be filtered is poured in. The flat
flexible receiver dilates automatically as the filtrate runs into it and
the funnel collapses as it empties. In the apparatus for carrying out
chemical or biochemical analyses the reagents dissolve in or disperse in
the filtrate from each preceeding compartment and yield colours,
precipitates or other reactions according to the known laws of science.
The apparatus can be hung in any convenient space by means of a clip, hook
or wire, and these may even be fabricated into the apparatus. However, the
actual means of suspension is not critical. In addition, the apparatus can
be sealed temporarily by folding over the top of the funnel compartment.
Thus it conveniently eliminates the possibility of airborne microorganisms
contaminating the fluids, or prevents the release of flammable or toxic
vapours. After use the apparatus can be discarded, thereby eliminating the
need for washing or removing identifying codes.
When said filter means is of a quality such as to remove pathogenic
microorganisms or is a membrane impermeable to dissolved salts my
invention provides a lightweight and portable source of potable water. For
example, it may be carried folded in a backpack then filled with impure
water and hung from the frame of a tent. In one embodiment a drinking
straw or tube may be sealed into the receiver so that the user can
withdraw purified water as necessary.
My invention thus provides a complete filtration apparatus which enables
filtrations or analyses to be carried out immediately, without the need to
assemble filter paper, funnel and receiver, or to add test reagents,
whereas previously these were required to be stored separately and to be
brought together before use, and to be washed out again where necessary
after the filtration. This simplifies and speeds up the process and can
reduce labour costs.
SUMMARY OF THE INVENTION
Apparatus in accordance with the invention will in the preferred form be
constructed from conventional filter means such as paper, cloth, cellulose
acetate or other cohesive porous sheet, and flexible single-ply or
laminated plastic film of a type that is easily joined by welding or
gluing and of a quality suited to the use to which the assembly is to be
put. Once familiar with the general principles of construction of the
apparatus as described herein the method of bringing together the
components and of joining them together by welding will be obvious to
anyone skilled in the art of making plastic bags and similar articles. In
its simplest form the filter means is not folded before being sealed into
the apparatus; however, if it is folded double and sealed in with the
crease at the bottom so that the crease intersects the direction of fluid
movement, as shown in the drawings, the mechanical strength of the
apparatus is considerably improved.
Four embodiments of the invention will now be described by way of example
with reference to the accompanying diagrammatic drawings in which:
FIG. 1a is a perspective view showing the relation of the folded filter
means and two plastic sheets before assembly, and FIG. 1b shows the side
elevation of a complete filtration apparatus in the preferred form in
which the filter means is folded double,
FIG. 2a perspectively shows a detail of the assembly around the entry point
of a straw and FIG. 2b the side elevation of this filtration apparatus in
which the receiver contains a drinking straw,
FIG. 3 shows an apparatus containing indicators of various chemical
properties and a plurality of compartments in which precipitation and
filtration can occur,
FIGS. 4a and 4b show a plurality of such apparatus for filtration or
chemical or biochemical analysis, illustrating how they can be stored on a
roll or in boxes.
Referring to FIGS. 1a and 1b, the filter means 1 is preferably a folded
rectangular filter paper, cloth or membrane, the size and aspect ratio of
said rectangle not being critical but preferably being chosen to suit the
use to which the apparatus will be put. For example, if the apparatus is
expected to filter out voluminous precipitates the aspect ratio may be
such that the folded filter means is as tall as, or even taller than it is
wide. If the apparatus is expected to filter out only small volumes of
precipitate it will be more economical to choose a filter means for which
the height is small in relation to the width. In general, wider filter
means will be chosen for filtration of larger volumes of fluid. While the
preferred shape is a rectangle other shapes are not excluded. For example,
a regular or symmetric hexagon before folding may be used, but may provide
less efficient filtration and be more difficult to fabricate. Likewise,
while the filter means is preferably folded double and preferably oriented
so that the crease will be downwards and intersecting the direction of
fluid flow when the apparatus is used other folds and orientations are not
excluded.
Said filter means 1 is folded along the line A--A and inserted between two
sheets of impermeable, flexible single-ply or laminated plastic film or a
single sheet of said film folded double. The two sheets of film are then
joined together and to the outer surfaces of filter means 1 at the places
indicated by the shaded area in FIG. 1b. The joining may be brought about
by means of conventional thermal or ultrasonic welding, whereby the
components are compressed between the opposed faces of welder dies shaped
according to the shape of said shaded area. Alternatively, said sheets of
film may first have applied to them by printing means a suitable fusible
or solvent-based adhesive before being brought together around said filter
means and bonded, for example, by being passed between opposed heated
rollers.
It will be seen that, in a filtration apparatus constructed according to
this description, receptacles (funnel 2 and receiver 3) capable of holding
the whole volume of fluid to be filtered are fabricated in one step and
that although they are at this stage lying flat and have no internal
volume thay will be capable of flexibly dilating to accept the fluid
poured into the apparatus as it passes through under the influence of
gravity. It will also be seen that the filter means separates but
internally connects the funnel 2 and receiver compartment 3 and is the
only route by which fluid can pass from one to the other. The small joins
4 are optional and may be added to provide extra support for the filter
means if the apparatus is very large. An optional hiatus in the otherwise
continuous join provides an outlet 5 which allows filtrate to be poured
out of the receiver. Alternatively, the join may be made continuous at 5
so that the receiver is completely sealed unless an orifice is made by
cutting the plastic film. The dimensions of the apparatus are relatively
unimportant but are preferably chosen so that the volume of the receiver
is at least as large as the volume of the funnel.
The apparatus may be fabricated either with or without regard for the means
by which it will be suspended when in use since almost any suspension
means will be acceptable and will, in any case, depend on the type of
support structure (hook, nail, rail, clothes-line, tent-frame, tree, etc)
available. For example, two sets of holes 6 may be provided so that the
funnel top may be folded along the line B--B and the apparatus hung from
hooks. Alternatively, the holes may be omitted so that the apparatus may
be hung up by a clip or pins, but any other method of sealing and hanging
such as a pliant wire or plastic closure combined with a handle is not
excluded. Whatever method is used, it will be seen that the funnel is
sealed from minor upsets and the entry of microorganisms or escape of
volatile solvent is minimized.
Referring to FIGS. 2a and 2b, an apparatus containing a drinking straw or
other tube 7 sealed into the receiver is shown. The numbers 1-6 have the
same meaning as in FIG. 1. To fabricate the apparatus the tube 7 is simply
inserted between the plastic sheets at a suitable angle and distance from
the crease of filter means 1 and becomes sealed in place when the
components are all joined together. The tube 7 is preferably of a
cross-section and flexibility that will allow it to be stored flat with
the rest of the apparatus, or it may be a more rigid tube around which the
apparatus is wrapped until use, but other forms and arrangements are not
excluded. The tube may also be sealed until use by a removable cap or
cuttable tip so that the entry of airborne microorganisms is prevented
until such time as fluid is withdrawn.
Referring to FIG. 3, a more complicated apparatus is shown in which certain
chemical test compartments and two filters are constructed. The numbers
1-6 have the same meaning as in FIG. 1 and the suffixes a and b refer to
the repeated components of the apparatus, which these may be repeated as
many times as is necessary. Each receptacle 3a, 3b etc., is of a volume
sufficient to hold the whole volume of fluid being filtered, so that even
if one filter means becomes impermeable to the filtering fluid filtration
will be completed through all of the stages above it. The porosities of
the various filter means will not necessarily be in a graded series but
will be chosen so as to be appropriate to the nature of any precipitate
formed in the receptacle above it by reaction of fluid with the reactant
sealed therein. This apparatus is useful for carrying out tests for
certain chemical or biochemical properties and by varying the number of
compartments and the reactants therein a number of analytical schemes are
possible. The test reagents may be inserted as pieces of impregnated paper
as shown, or as powders, or in specially formulated inks which are printed
onto the plastic film or the filter paper before the apparatus is sealed
together. Very many combinations of tests are possible and the reagents
and their quantities and method of retainment in the apparatus must be
chosen according to the use to which the apparatus is to be put. To use
the apparatus a solution or suspension is poured into the funnel 2 and
passes through the first filter 1a into receiver 3a where it reacts with
indicator 8 which may be, for example, lead acetate which forms a black
precipitate in the presence of sulfide. The filtrate passes through filter
1b into receiver 3b where it reacts with indicator 9 which may be, for
example, silver nitrate which forms a characteristic precipitate in the
presence of chloride, bromide or iodide. It should be noted that this
apparatus carries out automatically and without effort a series of tests
which previously required a considerable amount of manipulative time.
Referring to FIG. 4a, large numbers of such apparatus can be stored on a
roll from which units can be removed by tearing along a perforation or by
pulling them from a backing sheet to which they are attached.
Alternatively, large numbers of the apparatus can be stacked above one
another as in FIG. 4b.
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