Liquid purification or separation – Portable receptacle with hood or closure
Reexamination Certificate
1999-10-22
2001-10-02
Savage, Matthew O. (Department: 1723)
Liquid purification or separation
Portable receptacle with hood or closure
C210S380100, C210S497010, C210S498000, C422S105000
Reexamination Certificate
active
06296763
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to improvements in filters.
BACKGROUND OF THE INVENTION
It is conventional to examine a biological sample, for example a faecal sample, by placing it in a first tubular receptacle which is then closed by a filter medium. The first tubular receptacle may be attached to a second one in axial alignment such that the sample will pass into the second receptacle from the first through the filter. Filtration can be achieved simply by standing the assembly with the first receptacle uppermost or it may be encouraged by shaking the joined receptacles and/or placing them in a centrifuge. Following the completion of filtration, particles trapped by the filter and/or precipitated to the closed end of the second receptacle can be removed for analysis.
A double-receptacle filtration system of this kind is particularly, although not exclusively, suitable for the treatment of faecal samples where it is desired to isolate and remove for analysis of parasites, their eggs and larvae which may be present in the sample. The handling of such samples is unpleasant and presents biological hazards so that the “closed” double-receptacle filtration system is particularly attractive. Hitherto, however, the filter medium used has most commonly been a disc of woven material or a molded lattice which can be fitted across the open mouth of the first receptacle. This is liable to become clogged and occluded by larger particles suspended in the sample, such as pieces of undigested food Moreover if the double-receptacle is placed in a centrifuge this will tend to drive particles through the filter into the second receptacle. For this reason filtering and centrifuging are normally done separately and this two-stage operation is time consuming and labor intensive, as well as representing a hazzard to the operator when the two receptacles are disconnected.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided a filtration assembly comprising a sample mixing receptacle closed at one end and open at its other end, a second receptacle having a closed end and an open end and adapted to be fixed in coaxial alignment with the mixing receptacle to receive filtrate from the latter when the two, joined receptacles are placed in a centrifuge and a stopper for the open end of the mixing receptacle, the whole assembly being adapted to be placed in a centrifuge, wherein a tubular filter extends from the center of the stopper such that when the mixing receptacle is stoppered a closed end of the filter confronts the closed end of the receptacle and an open end of the filter opens through the stopper, the stopper providing a shoulder around the filter at the open end of the mixing receptacle.
The tubular filter provides an enlarged filter area by comparison with a disc filter, but a more important advantage is that centrifugual forces, instead of driving particles through the filter will instead drive them off the filter and toward the shoulder, where they will be retained when the two receptacles are subsequently disconnected. This means that filtration and centrifugeing can be carried out as a single operation. There is less danger of contamination of the sample in the second receptacle and the two receptacles can be disconnected without exposing the operator to the residue in the first receptacle.
Preferably the stopper is adapted to make screw-threaded connections to both of the receptacles and means is provided whereby the second receptacle is preferentially unscrewed from the stopper when the two receptacles are oppositely twisted.
The filter preferably comprises a lattice structure of crossing, elongated elements of which at least those presented outwardly of the filter tube extend outwardly of the filter with respect to the plane of the pores formed by the crossing elements, thereby to provide ribs on the exterior of the lattice which will act as a pre-filter for larger particles in advance of said pores. The interior of the filter tube is preferably additionally ribbed, the internal ribs extending longitudinally of the filter tube and the external ribs extending transversely thereof.
It is known that tubular filters can be made by molding a plastics material into a lattice formation. However the porosity of such a “lattice” is considerably inferior to that of a woven filter, i.e. the pores of a molded filter are relatively few in relation to the total filtration area, so that it is not apparent that this alternative would be an improvement.
In accordance with a preferred embodiment of the present invention the filter comprises a lattice structure of crossing, elongated elements of which at least those presented outwardly of the filter tube extend outwardly of the filter with respect to the plane of the pores formed by the crossing elements, thereby to provide ribs on the exterior of the lattice which will act as a pre-filter for larger particles in advance of said pores.
Preferably the interior of the filter tube is additionally ribbed, the internal ribs extending longitudinally of the filter tube and the external ribs extending transversely thereof.
An advantage of this arrangment is that occlusion of part of the length of a channel defined by two adjacent ribs by a large particle will not occlude the pore or pores confronted by the trapped particle, because liquid will still reach said pore or pores along the channel beneath the particle. It has been calculated that particles just large enough to be trapped by the ribs can confront each pore within the lattice without any observable restriction of the flow of liquid through the filter. If the depth of the ribs is increased then larger particles can confront several pores within the lattice without any observable restriction in the flow through the filter.
In a molded, tubular construction any internal ribs must be longitudinal as otherwise it would be impossible to remove the mould core. Effectively this means that any external ribs must be transverse (the outer mould part being separated into two halves to remove it from the molded filter). Transverse external ribs on a tubular filter formation have a dual advantage. During manufacture and while the filter is still contained in the external mould part they serve to anchor it while the mould core is withdrawn from the interior of the filter. When the filter is in use the fact that the external ribs are transverse means that the channels formed between them are at right angles to the “natural flow” of the liquid sample out of the first receptacle. Causing the liquid to change direction to enter the channels enhances filtration by creating a greater tendency for larger particles to be trapped by the “pre-filter”.
REFERENCES:
patent: 751918 (1904-02-01), Jagger
patent: 916340 (1909-03-01), Lewis
patent: 2579863 (1951-12-01), Robinson
patent: 5545318 (1996-08-01), Richmond
patent: 298513 (1993-05-01), None
patent: WO 93/10433 (1993-05-01), None
DiaSys Europe Limited
Nixon & Peabody LLP
Savage Matthew O.
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