Liquid Filtration Device

The present invention relates to a liquid filtration device of the type adapted to separate a liquid from solid particles, and is applicable notably to the filtration of a coffee infusion either in a household coffee machine or in a percolator.

Metal filters either in the form of perforated discs with or without raised edge, or in the form of a bell, are already known. Since the holes of these filters are extremely small, of the order of 0.15 to 0.2 mm, they clog inevitably. In this case, the only solution consists in clearing the hundreds of holes one by one with a pin.

In percolators pertaining to the pressure filter type filtration occurs under a certain pressure and the filter medium must have an adequate strength, and therefore a minimum thickness. To avoid any increment in the risk of clogging, it is known to flare the orifices out in the direction of flow. But also in this case the holes clog up rapidly as in thin filters.

It is the essential object of the present invention to provide a filtration device for liquids which is based on a different principle consisting in substituting one or several slots for the conventional orifices.

This device consists in juxtaposing at least two members so as to provide therebetween at least one slot of a width corresponding to the order of magnitude of the solid particles to be filtered, said slot flaring out in the direction of flow of the liquid.

FIG. 1 illustrates in vertical axial section the filter device according to a preferred embodiment of the invention, inserted in a percolator;

FIG. 2 illustrates in axial section a modified embodiment of the two filter-forming members;

FIG. 3 is a view similar to FIG. 2 but showing means for adjusting the relative position of the two members; and

FIGS. 4 and 5 illustrate in plan view from above and in vertical axial section, respectively, ribs or shims for centering the two members in relation to each other.

Referring to FIG. 1, it will be seen that a first member 1 consists of a cup or inverted bell-shaped cylindrical body having its top aperture partially closed by another member 2 of substantially frustoconical configuration, generally disposed in the cup 1 so as to leave a gap 3, the major and upwardly facing, upper base of this member 2 constituting and inner wall and particularly shown the bottom of the filtration chamber 6 and being, as shown, approximately flush with the upper, inner edge 1a of cup 1. The partial closure or valve member 2 has a minor, lower base 5 adjacent to and opposite the bottom 1b of the cup 1. Base 5 is formed with a blind hole engaged by a fitting member or support 23 centered with precision in the bottom of the first, cup-shaped member 1. This cup-shaped member 1 further comprises a tube 22 extending through its bottom to permit the escape of filtered liquid, for example coffee or another infusion to the outside. FIG. 1 also shows how the filter device of this invention can be adapted to a percolator, since the cup-shaped body or member 1 may act as a piston slidably fitted in the bore of a cylinder 19 and movable under the control of suitable actuating means, designated only diagrammatically by the arrow F, for compressing the ground coffee in the filtration chamber 6 against another piston 20, hot water being injected through another pipe 21. By properly moving the pistons 1 and 20, the coffee-grounds are expelled when necessary, after the coffee has filtered through the slot 3.

FIG. 2 shows a modified embodiment in which the valve-like member constitutes a kind of short cylinder 2' provided with a shouldered base 9, a centering shank 10, and a screw-threaded extension 11 of this shank adapted to be engaged by a nut. The hollow or cup-shaped member 1' has a cylindrical outer and frusto-conical inner configuration with a concentric bore increasing in diameter from the upper, inner edge 7 inwards, down a level designated by the reference numeral 8, so that the width of the slot 3 formed between the cup 1 and cylinder 2 increases outwardly and downwardly, as shown.

FIG. 3 illustrates how the relative positions of members 1 and 2 may be modified by means of a modified support for the valve member 2. Instead of the support 23 of FIG. 1, this embodiment uses a support 16 having an upwardly facing shoulder; supporting, below the member 2, a suitable number of washers 18 in order to permit a convenient adjustment of the width of slot 3 and therefore the fineness of the filtration. In this case the support 16 and thereby the frustoconical member 2 is secured to the bottom of cup-shaped member 1 by means of a knurled nut 17.

FIGS. 4 and 5 illustrate in plan view and in section respectively a modified embodiment in which the width of slot 3 is maintained by means of ribs or shims 13, integral with cup 1.

In this modified embodiment the frustoconical member 2" bears directly with its minor base 14 on the bottom of the cup-shaped member 1. The two members are assembled by means of a screw 15, the relative centering being provided for by the aforesaid ribs or shims 13.

Of course, the filtration device according to this invention can be operated both vertically, as shown in the drawing, and horizontally; in this last case, the infusion outlet tube 22 is disposed radially, as illustrated in FIG. 5.

The frustoconical member and cup-shaped members illustrated in the drawing are solid members machined or cast integrally; however, other manufacturing methods may be used such as stamping, embossing, punching or injection moulding (in the case of cast-iron).

A possible improvement, notably when the filter of this invention is intended for a percolator, consists in providing suitable means for causing a relative movement between the two members 1 and 2 in order to release any solid particles likely to adhere to the edges of the slot 3.

It will readily occur to those conversant with the art that various modifications and changes may be brought to the filter described and illustrated herein without departing from the basic principle of the invention.