The present invention generally relates to filters for liquids containing solid particles, specially lubri-refrigerants coming from machine tools.

More particularly, the scope of the invention is a self- cleaning filter of the type comprising: -a casing circumscribing a first vertical axis chamber, possessing a side inlet duct for the liquid to be filtered; -a discharge valve normally arranged on a closed position on the bottom of the first chamber; -a perforated cylindrical wall arranged on a coaxial direction within the casing and a bottom wall; -an elongated cylindrical body arranged in a coaxial direction within said perforated cylindrical wall, projecting from the upper portion of said perforated cylindrical wall, the latter being closed on the upper portion thereof, said elongated cylindrical body defining a second chamber closed on the lower portion thereof by said bottom wall.

-an outlet duct laterally connected to said elongated cylindrical body by a cable for discharge of the filtered liquid, within a collection pan; -a filtering element lining said perforated cylindrical wall; -an axially and hermetically arranged sliding cylinder within an elongated cylindrical body, normally arranged in an upper position; -a stem connecting said piston to said discharge valve through said bottom wall; -an actuator to control the displacement of said stem from an upper position to a lower position, to perform the opening of said bottom valve and the simultaneous downward displacement of said piston along said cylindrical body, so as to cause a backflow of the filtered liquid from said second chamber into said first chamber through said filtering element; -a check valve connected to said outlet duct, to allow the introduction of air into said elongated cylindrical body during the downward displacement of said piston.

A self-cleaning filter of the type defined above is known from the American patent US 4.271.019 granted to the applicant hereof. In this filter, the backflow of filtered liquid from the second chamber into the first chamber performs the counter-current washing of the filtering element, causing the detachment of the solid particles filtered by said filter and the elimination thereof through the open bottom valve. The cleaning cycle is conveniently controlled in an automatic fashion, once a pre-established degree of encrusting of the filtering element is reached.

The present invention is an improvement of said known filter, and the particular object thereof is to improve the discharge of the filtered liquid, preventing it from contaminating the environment externally of the pan without however reducing the efficiency of the filter's self-cleaning cycle.

A further object of the invention is to additionally improve the functional efficiency of the filter, also in relation to the emissions of the liquid to be filtered.

In accordance with a first aspect, the filter pursuant to the invention is mainly characterized in that said outlet duct includes a substantially vertical discharge tube that ends in said filtered liquid contained in said collection pan and being provided with a side outlet passage arranged at a level above the maximum level of the filtered liquid in said collection pan.

Thanks to this solution idea, during the filter's normal operation, the filtered liquid is taken into the collection pan without risks of dripping and dispersions in the outer ambient, and the lateral outlet allow to eliminate eventual overpressures of the filtered liquid in the outlet duct. During the filter's cleaning cycles, the lateral outlet allows the discharge into the atmosphere of the residual air contained in the outlet duct through the check valve, thereby preventing bubbling, and also foam formation in the filtered liquid (generally including oil in water emulsions) contained in the collection pan.

According to a preferred manner of operation of the present invention, said outlet is formed of an open, horizontal tubular appendix open on the lower portion of said substantially vertical discharge tube.

According to another aspect of the invention, said lateral inlet duct for the liquid to be filtered is associated to a deflector arranged within said first chamber, to direct the flow of liquid to be filtered substantially against the inner wall of said casing.

This characteristic allows to prevent that the flow of liquid to be filtered be directly sent against the filtering element, thereby limiting the wear and at the same time reducing the formation of foam inside the filter's first chamber.

The invention will now be described in a detailed manner with reference to the appended drawings, provided solely by way of non-limiting examples, wherein: -Figure 1 is a schematic, partial axial section view of a filter according to the invention, represented during the filtering cycle; -Figure 2 is a view similar to Figure 1, showing the filter during the self-cleaning cycle;

-Figure 3 is an enlarged, partial side elevation view showing the filter's casing; -Figure 4 is a horizontal cross-section view according to line IV-IV of Figure 3; -Figure 5 is an enlarged, elevation view of a detail of Figures 1 and 2; -Figure 6 is a lower plan view according to arrow VI of Figure 5; and -Figure 7 is an enlarged, cross-section view according to line VII-VII of Figure 5.

The filter illustrated on the drawings comprises an outer, cylindrical, vertical axis casing 1 provided on the lower portion thereof with a truncated cone wall 2 formed with a central opening 3 normally closed by the valve actuator 4 having an inverted truncated cone shape supported with interposition of a power spring 5 on the lower portion of a vertical stem 6.

The casing 1 is entirely hermetically sealed by an annular flange 7 and communicates laterally with an inlet 8 for the liquid to be filtered. In the case of the illustrated example, the duct 8 has an elbow shape and, according to a particular aspect of the invention detailed on Figures 3 and 4, in correspondence with its nozzle communicating with casing 1 is provided a deflector 9, the function of which will be presently explained.

Inside casing 1 is coaxially arranged a perforated cylindrical wall 10 that is attached on the upper portion thereof to the annular flange 7 and is closed on the lower portion thereof by a bottom wall 11 hermetically and slidingly crossed by a stem 6.

The perforated wall 10 is lined with an annular filtering element 12 that can be comprised of a metallic mesh or by a textile, for example, of synthetic material, the density of which is in accordance with the nature of the particles to be retained thereby.

The space externally circumscribed by casing 1 with the truncated-cone shaped wall 2 and the upper flange 7 and internally by the perforated wall 10 with the bottom wall 11 comprises a first filter chamber 13. Such first chamber 13 communicates laterally with the inlet duct 8 and can be connected on the lower portion thereof, at the opening position of valve 6, with a discharge container 14.

The inlet tube 8 is destined to be connected to the outlet of a pump (not shown) the purpose of which is to feed under pressure to the first chamber 13 the liquid to be filtered.

With 15 is indicated an elongated cylindrical body arranged in a coaxial direction within the perforated wall 10, through the annular flange 7, to which such cylindrical body 15 is rigidly attached, so as to project upward from the casing 1.

The elongated cylindrical body 15 is open on the lower portion thereof and is closed on the upper portion thereof by a cover 16 which is crossed in a sealing manner by stem 17 of a linear actuator comprised of a double- effect pneumatic or hydraulic hammer 18. To the stem 17 is attached a piston 19 assembled in a sliding manner along the elongated cylindrical body 15. Normally, and as illustrated on said American patent US 4,271,019, the piston 19 is comprised of a rigid disc and a larger-diameter lower disc of elastomeric material capable of performing a sliding and sealing contact along the elongated cylindrical body 15 during the vertical displacement of piston 19.

To the lower portion of piston 19 is rigidly attached the stem 6 supporting the valve plug 4.

The gap externally defined by the perforated wall 10 with the bottom wall 11 and internally by the elongated cylindrical body 15 with cover 16 defines a second chamber 20 destined to be traversed by the filtered liquid.

The volume of the second chamber 20 is variable between a maximum value, corresponding to the fully raised position of piston 19, as shown on Figure 1, and a minimum value corresponding to the fully lowered position of piston 19, as shown on Figure 2.

The elongated cylindrical body 15 communicates, at a small distance from the cover 16, with an outlet duct indicated as a whole by 21, including a horizontal portion 22 laterally connected to the elongated cylindrical body 15 and a vertical portion 23 for discharge of the filtered liquid in a collection pan 24, from which said filtered liquid is sent for reutilization. Between the horizontal portion 22 and the vertical portion 23 of the outlet duct 21 is arranged the fitting 25, to which is fitted a check valve 26 (of the usual type, but assembled in counterflow) capable of allowing, as described below, the introduction of air inside the second chamber 20 during the filter's self-cleaning cycle. The shape of the check valve 26 can be analogous to the one described on said document US 4,271,019.

In accordance with another particular characteristic of the present invention, the length of the vertical portion 23 of the discharge duct 21 is such that its lower end, indicated by 27, is constantly submerged in the collecting pan 24, or is then arranged below the maximum level of such liquid, indicated by L on pan 24. At a certain distance from the lower end 27, the vertical portion 23 of the outlet duct 21 is provided with a vent which, in an opposite manner, is constantly arranged at an upper level in respect of the maximum level L of the filtered liquid in the collection pan 24. As illustrated in detail on Figures 5 through 7, such vent is conveniently comprised of a

horizontal tubular appendix 28 communicating on one side with the outlet duct 21 and closed on the opposite portion, formed on the lower portion thereof with a longitudinal opening 29 facing downwards and eventually also at a certain angle in respect of the horizontal plane. The opening 29 can be replaced by a series of orifices or similar openings facing the surface of the filtered liquid in the collecting pan 24.

In the first chamber 13 is inserted a pressure gage 30 capable of generating-when the pressure value of said chamber exceeds a predetermined threshold-a pulse that is transmitted to an electric servo control 31 associated to a distributor 32 that controls the operation of hammer 18. The system, known in itself, and accordingly not described in detail, is arranged in the retracted position, as shown on Figure 1, corresponding to the raised position of piston 19 and the closing of valve plu 4, when the pressure inside the first chamber 13 is below said threshold and, contrariwise, assumes the extended position shown on Figure 2, corresponding to the lowered position of piston 19 and to the condition of opening of plug 4, when the value of said pressure exceeds said threshold.

The operation of the filter in accordance with the invention is as follows: The liquid under pressure to be filtered comes from the inlet duct 8 and passes from the first chamber 13 to the second chamber 20 by crossing the filter element 12 and the perforated wall 11 and then reaches the discharge duct 21. The presence of deflector 9 associated to the inlet duct 8 prevents the incoming liquid from directly hitting the filter element 12 and causing damage thereto. In fact, such deflector 9 allows to obtain at the inlet of the first chamber 13 a substantially laminar rotating flow of the liquid to be filtered, thereby reducing the turbulence and the formation of foam by effect of the oil emulsion normally present in the lubri-refrigerant liquid to be filtered.

The section of passage of the liquid through the filter element 12 is selected so that the pressure inside chamber 13 is normally lower than the threshold described for a given flow intensity. Accordingly, under such conditions, the second chamber 20 communicates with the outlet duct 21 and, accordingly, with the collecting pan 24. The filtered liquid, the pressure of which inside duct 21 maintains check valve 26 closed, is then discharged inside the pan 24 below level L of already filtered liquid present therein. In this situation, the vent comprised by tubular appendix 28 and arranged above level L does not perform any other function besides that of discharging eventual liquid overpressures inside the outlet duct 21.

The deposit of solid particles on portions of the filter

element 12 and arranged facing the orifices of perforated wall 10 gradually reduces the flow of liquid through such orifices and, accordingly, causes a progressive increase in the pressure in the first chamber 13 of the filter. When such pressure exceeds the threshold to which the pressure gauge 30 has been adjusted, the latter sends a signal to the servo command 31 and determines the switching of distributor 32, which actuates the hammer 18 to the effect of quickly lowering stem 17 with stem 6, thereby arranging the piston 19 in the lower stop position and the plug 4 in the opening position, as shown on Figure 2. Evidently, this causes the opening of the bottom of chamber 13 and sudden decrease of the volume in the second chamber 20, which generates a countercurrent flow of the already filtered liquid from the second chamber 20 towards the first chamber 13, through the orifices of wall 10. The displacement and disposal of particles adhered to the filter element is thus achieved, jointly with the filtered liquid flowing towards the first chamber 13, in the direction of container 14, through the bottom opening 3.

The quick descent of piston 19 is speeded up by the opening of valve 26, caused by the suction achieved in the portion 22 of the outlet duct, which allows the inflow of air inside the upper zone of the elongated cylindrical body 15.

At this stage, the vent comprised by the tubular appendix 28 allows the discharge inside the pan 24 of the liquid contained in the upper zone of the vertical portion 23 of outlet duct 21.

The discharge of the liquid and the impurities from the first chamber 13 determines in the later a pressure drop below the threshold. This is again detected by the pressure gage 30 which, through the servo control 31 and distributor 32, actuates the hammer 18 in the opposite direction, to raise again stem 17 with stem 6, replacing piston 19 in the upper position and plug 4 in the closing position, as shown on Figure 1, thereby resuming the filter's normal operation.

Naturally, the construction details and the manners of operation can be amply varied in respect of what has been described and illustrated herein, without departing from the scope of the present invention, as defined on the following claims. Accordingly, for example, the filter may comprise means to allow a manual control for operation of actuator 18, jointly with or in an alternate manner in respect of the automatic operation previously described.