Liquid filtration device

A filter, mainly for coffee-making devices, comprises a cup-shaped cylindrical member and a circular member partially closing the top aperture of the cup-shaped cylindrical member so as to leave a filter-forming circular gap therebetween. This gap increases in width from the inner edge of the cup-shaped member inwards; the top face of the circular member may constitute the bottom of the filtration chamber. Means may be provided for adjusting the relative spacing of these members and therefore the width of the filter-forming gap. Ribs or shims may be provided on either of the two members for maintaining a permanent gap width.

BACKGROUND OF THE INVENTION 
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. 
SUMMARY OF THE INVENTION 
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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
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.