FILTER ARRANGEMENT DESCRIPTION OF THE INVENTION The present invention relates to a filter arrangement for extracting solid particles from a flowing liquid, the arrangement of a kind that includes a filter box being at least one tubular filter that is mounted on the box, so that the liquid flows through the filter wall and an inlet for the liquid and an outlet for the liquid. A filter or screen arrangement of the kind mentioned is known from German patent document DE1536939. In this case, the tubular filter is placed in the mucus filter housing, where one end of the filter captures the entire liquid flow, while the other end rests against the internal surface of the filter housing to prevent the liquid flow through the end of the filter. The object of the present invention is to provide a novel filter arrangement that is especially improved as regards the flow of liquid therethrough. Therefore, it is proposed according to the invention, that in the case of a filter arrangement of the kind defined in the introduction, the mutually reinforcing ends of the filter or of each are arranged so that the liquid flows simultaneously to the filter. through its ends, and that the filter is surrounded by an internal box mounted in the filter box and spaced from the walls thereof, so that the opposite ends of the filter are left free, wherein the inside of that internal box or cover is connected, either to the entrance or exit, preferably to the exit, as long as the space between the filter box and the inner cover is connected to the entrance or exit, preferably to the entrance. This arrangement achieves an advantageous reduction in the resistance to flow through the filter, and also uses the total filtering area more evenly. Another advantage is that heavier particles can follow the wall of the filter box to the bottom of the box without penetrating the filter or filters. The filter box can conventionally be provided in its lower part with an opening through which the particles that have been collected in the bottom of the box can be removed. The filter box or the inner cover has a rounded shape, for example spherical, thus obtaining low flow resistances, which is favorable. From the aspect of the liquid flow, this is favorable for the combined area of the filter end to generally coincide with the entrance area of the filter array. When the filter box is typically provided with a bottom tube that can be closed with a removable cap or hood, the inner cover can advantageously be provided with a bottom opening that is opposite the tube and through which the filter or filters can be removed. of the cover and the filter box, for example, for cleaning purposes, and then return to the filter box and removably mounted on the inner cover. This allows the filter or filters to be conveniently locked in their working position in the inner box. For example, the filter or filters may be provided with a handle to facilitate the removal and replacement thereof, and to coloborate with a locking device that can be moved manually to one side and that functions to removably block the filter in the inner cover. When the filter arrangement includes a plurality of filters disposed side by side, the filter ends can be adjusted with end plates that function to hold the filters together and make bridges by sealing the spaces between the filter openings. A particular advantage is obtained when the filter arrangement is integrated with a gas separator connected directly, either to the input or output of the filter arrangement. According to a preferred embodiment, the filter arrangement and gas separator include a generally cylindrical outer casing, which is common to both the filter array and the gas separator, and which when used has at least one horizontal axis, wherein the filter array and the gas separator are mutually separated by a dividing wall extending transversely in the box, and where there is a tube through which the liquid flows and that has an open upper part, through which the gas bubbles can rise when rising, a tube that extends in the gas separator between one end of the outer cover and the dividing wall. Now, the invention will be described in more detail with reference to several exemplary embodiments and in relation to the accompanying drawings in which: FIGURE 1 is a vertical axial sectional view of a first embodiment of a filter arrangement according to the invention along line II, in Fig. 2; FIGURE 2 is a horizontal sectional view taken on line II-II, in Fig. 1; FIGURE 3 is a vertical cross-sectional view of the arrangement shown in FIGS. 1 and 2; FIGURE 4 is a view corresponding to FIG. 1, and illustrating a second embodiment of the inventive filter arrangement; FIGURE 5 is a horizontal sectional view taken on line V-V, in Fig. 4; FIGURE 6 is a vertical axial sectional view of a combined filter and gas separator arrangement according to the invention; FIGURE 7 is a cross-sectional view taken on line VII-VII, in FIG. 6; and FIGURE 8, is a view corresponding to FIG. 6, and illustrating another combined mode of filter arrangement and gas separator according to the present invention. Corresponding or in general corresponding components of the illustrated modalities are indicated with the same figure. The filter arrangement shown in Figs. 1-3, comprises a filter box 1, a cylindrical filter 2, which is open at both ends and an inner cover or cage 3, the figure 4, identifies an entry for the liquid to be filtered during its passage through the filter arrangement, while figure 5 identifies a liquid outlet. The inlet 4 is connected to the filter box 1, while the outlet 5 is connected to that part of the inner cover 3, which surrounds the filter 2. The inner cover 3, and the filter ends are spaced from the surface internal of the filter box 1, and the inner cover is provided with the upper and bottom openings 6, 7, which are configured to free the mutually opposite openings of the filter 2, for the simultaneous flow through the liquid. The filter 2 is maintained in the correct position in the inner box 3, with the help of a flange 8, upper locating the filter directed inwards, against the interior of which the upper end of the filter 2 is pressed, by means of a locking device (described in greater detail below), to removably but firmly lock the filter 2, in its working position in the inner cover 3. It is provided opposite to the bottom opening 7, of the cover internal 3, a bottom tube 9, which can be closed by means of a removable hood 10. The hood 10 is fixed with the aid of a flange gasket formed by the flanges 11, 12, on the tube and on the hood respectively, thus, as with the bolts 13. the hood is sealed by means of a ring -014, received in the peripheral groove in the hood 10. The hood 10, is provided with a central opening 15, which allows the particles that have been put together in tube 9, it was emptied in and that can be sealed with a plug or something similar that is not shown. The entire hood 10 is removed when you want to remove the filter 2, for example, for cleaning purposes. The filter 2 is provided with a handle 16, in the form of an agitator that facilitates the removal of the filter 2 from the filter box. The filter 2 can be locked in its working position in the internal cage 3, by means of a blocking device provided for this purpose. In the embodiment shown in Figs. 1-3, the locking device includes an angled leaf spring 17, which is connected to the inner cover 3, and a leg of which generally extends diagonally over most of the opening 6. As is best appreciated by the Fie ?. 3, the leg has a connection with a bar 18, which generally extends centrally downwardly through the filter 2, and whose bottom end includes U-shaped upper and lower parts 19, 20, which are bent outwardly. in mutually opposite directions, of those parts, the lower part 20, is intended to grip around the handle in the form of agitator 16, in the manner illustrated, and with this, hold the upper end of the filter 2, pressed against the flange 8 The curved part, top 19, it functions as a handle to urge or force the part 20, down against the action of a spring 17, and to one side out of engagement with the filter handle 16, after removing the hood 10, to allow the filter 2, it is removed from the cover or cage 3, and from the filter box 1. The filter box 1, and / or the inner cover 3, can conveniently have a spherical shape thus reaching advantages with respect to mechanical strength and with respect to the Fluid flow through the arrangement. The combined area of the filter end will preferably be the same as the area of the inlet 4, and basically equal to the area of the outlet 5. This will result in a relatively low pressure flow through the filter array when the liquid flow enter through the inlet 4, through the inside of the filter box 1, and get to the outside of the inner cage 3, and then, through the openings 6, 7, and from there to the filter 2, from where the liquid comes out through of the filter wall leaving leaving particles and leaving the outlet 5. Because the liquid flows to the cylindrical filter 2, from both ends thereof, in general, the filtering surface and the area centrally of the filter will be uniformly used with a cleaning opening that is missed by a screw cap 23. The remaining components of the arrangement shown in Figs. 4 and 5, have been identified by the same reference figures as those used to identify corresponding components of the modality shown in Figs. 1-3, and will not be described in detail. The use of a plurality of tubular filters 2A allows the total filtering area to be increased without increasing the volume of the filtering assembly. The particles extracted from the liquid flowing through the filter array are essentially collected on the removable bottom 10 of the filter box 1. The bottom part of the filter box 1 forms a tube turn corresponding to the return of the tube 9 in Figures 1- 3. Figures 6 and 7 illustrate an embodiment wherein the filter arrangement corresponding in all essentials to the filter arrangement shown in Figures 1-3 is combined with a gas separator. Such a gas separator can be advantageously used in a circulating liquid system, since the presence of gas, for example air in the system operating with heat carried by water, tend to low efficiency and cause the presentation of cavitation in circulation pumps, the gas separator and the filter arrangement includes a common exterior box 1A in the form of a horizontal cylinder having arcuate or curved ends and separated by a transverse partition wall 24. The gas separator has an inlet 25 and an upper part and bottoms are lockable at the tube ends 26, 27 through which collected gas and collected solid particles or waste can be removed as required, extending centrally through the interior of the gas separator between inlet 25 and dividing wall 23 there is a tube 28 whose upper part is largely open, as shown at 29, and the downstream end 30 passes through the wall. d divider 24 forming the filter arrangement entrance. The gas bubbles accompanying the liquid as it passes through the gas separator are able to separate upwardly from the tube 28, through its open part 29, to finally collect at the top of the gas separator. The solid particles can also be separated from the liquid to some extent, these particles are removed through the pipe section 27. As best seen in Figure 7, the desired flow template through the gas separator is improved with the help of flaps 31. The liquid entering the filter array through the tube end 30 is filtered in the manner described with reference to Figures 1-3. The embodiment illustrated in FIG. 8 differs from the embodiment illustrated in FIGS. 6 and 7 only in that the filter array is located forward of the gas separator constructed therein together. The liquid filtered or passed through the filter exits through the outlet of the filter box, from where it passes through the end 30 of the partially open tube 28 and leaves the gas separator through the tube section 25. It is appreciated that the invention will not be restricted to the modalities described and illustrated, but that there are multiple changes and modifications without departing from the spirit and scope of the present invention.