The present invention relates to a filter arrangement for extracting solid particles from a flowing liquid, said arrangement being of the kind which includes a filter housing, at least one tubular filter which is mounted in said housing so that the liquid will flow through the filter wall, and a liquid inlet and outlet.

A filter or screen arrangement of the aforesaid kind is known from DE 1 536 939, for instance. In this case, the tubular filter is positioned in the filter housing so that one end of the filter captures the whole of the liquid flow, whereas the other end of the filter lies against the inner surface of the filter housing such as to prevent liquid from flowing through this end of the filter.

The object of the present invention is to provide a novel filter arrangement which is particularly improved with regard to the flow of liquid therethrough.

Accordingly, it is proposed in accordance with the invention that in the case of a filter arrangement of the kind defined in the introduction the mutually opposite ends of the filter or of each filter are disposed so that liquid will flow simultaneously through both of said ends, and that the filter or filters are surrounded by an inner casing mounted in the filter housing and spaced from the walls thereof such as to leave the mutually opposite filter ends free, wherein the interior of said inner casing is connected to either the inlet or the outlet, preferably the outlet, while the space between the filter housing and the inner casing is connected to the other of said inlet or outlet, preferably the inlet. This arrangement achieves an advantageous reduction in the resistance to flow across the filter or filters, and also utilizes the total filter area more uniformly. Another advantage is that heavier particles are able to follow the

wall of the filter housing to the lower part of said housing, without entering the filter or filters. The filter housing may be provided conventionally in its lowermost part with an opening through which particles that have collected on the housing bottom can be removed.

The filter housing and/or the inner casing suitably has a rounded, e.g. spherical shape, thereby obtaining favourable, low flow resistances. From the aspect of liquid flow, it is also favourable for the combined filter-end area to coincide generally with the inlet area of the filter arrangement.

When the filter housing is typically provided with a bottom pipe stub that can be closed with a removable cap, the inner casing can be provided advantageously with a bottom opening which lies opposite the pipe stub and through which the filter or filters can be removed from the casing and from the filter housing for cleaning purposes for instance, and thereafter returned to the filter housing and mounted detachably in the inner casing. This enables the filter or filters to be conveniently locked releasably in its/their working position or working positions in the inner casing. For instance, the filter or filters may be provided with a handle for facilitating the removal and replacement thereof and for coaction with a locking device that can be moved manually to one side and which functions to releasably lock the filter or filters in the inner casing. When the filter arrangement includes a plurality of filters placed side-by- side, the ends of the filters may be fitted with end plates which function to hold the filters together and which sealingly bridge the spaces between the filter openings.

A particular advantage is obtained when the filter arrange¬ ment is integrated with a gas separator connected directly to either the inlet or the outlet of said filter arrangement. According to one preferred embodiment, the filter arrangement and the gas separator include a generally cylindrical outer

casing which is common to both the filter arrangement and the gas separator and which in its state of use has an at least generally horizontal axis, wherein the filter arrangement and the gas separator are mutually separated by a partition wall that extends transversely in the casing, and wherein a pipe through which the liquid flows and which has an apertured upper part through which rising gas bubbles can depart extends in the gas separator between one end of the outer casing and said partition wall.

The invention will now be described in more detail with reference to a number of exemplifying embodiments thereof and also with reference to the accompanying drawings, in which

Fig. 1 is a vertical axial section view of a first embodi¬ ment of an inventive filter arrangement, said view being taken on the line I-l in Fig. 2; Fig. 2 is a horizontal sectioned view taken on the line II- II in Fig. 1; Fig. 3 is a vertical cross-sectional view of the arrangement shown in Figs. 1 and 2; Fig. 4 is a view corresponding to Fig. 1 and illustrating a second embodiment of the inventive filter arrange¬ ment; Fig. 5 is a horizontal sectional view taken on the line V-V in Fig. 4; Fig. 6 is a vertical axial section view of a combined filter arrangement and gas separator in accordance with the invention; Fig. 7 is a cross-sectional view taken on the line VII-VII in Fig. 6; and

Fig. 8 is a view corresponding to Fig. 6 and illustrating another embodiment of a combined filter arrangement and gas separator according to the present invention.

Corresponding or generally corresponding components of the illustrated embodiments have been identified with the same

reference signs.

The filter arrangement shown in Figs. 1-3 comprises a filter housing 1, a cylindrical filter 2 which is open at both ends thereof, and an inner casing 3. The reference numeral 4 identifies an inlet for liquid to be filtered or screened during is passage through the filter arrangement while the reference numeral 5 identifies a liquid outlet. The inlet 4 is connected to the filter housing 1, whereas the outlet 5 is connected to that part of the inner casing 3 which surrounds the filter 2. The inner casing 3 and the ends of the filter are spaced from the inner surface of the filter housing 1, and the inner casing is provided with top and bottom openings 6, 7 which are configured so as to leave the mutually opposite openings of the filter 2 free for the simultaneous throughflow of liquid. The filter 2 is held correctly positioned in the inner casing 3 with the aid of an upper, inwardly directed filter localizing flange 8, against the inside of which the upper end of the filter 2 is pressed by means of a locking device ( described in more detail below) for detachably locking the filter 2 firmly in its working position in the inner casing 3.

There is provided opposite the bottom opening 7 of the inner casing 3 a bottom pipe stub 9 which can be closed by means of a removable cap or cover 10. The cap 10 is fastened with the aid of a flange joint formed by flanges 11, 12 on the pipe stub and on the cap respectively, and bolts 13. The cap, or cover member, is sealed by means of an O-ring 14 received in a peripheral groove in the cap 10. The cap 10 is provided with a central opening 15 which allows particles that have collected in the pipe stub 9 to be emptied and which can be sealed with a plug or like device, not shown. The entire cap

10 is removed when wishing to remove the filter 2 for cleaning purposes, for instance.

The filter 2 is provided with a stirrup-shaped handle 16

which facilitates removal of the filter 2 from the filter housing. The filter 2 can be locked in its working position in the inner casing 3 by means of a locking device provided to this end. In the embodiment shown in Figs. 1-3, the locking device includes an angled leaf spring 17 which is connected to the inner casing 3 and one leg of which extends generally diagonally over the larger part of the opening 6. As will best be seen from Fig. 3, said leg has attached thereto a rod 18 which extends generally centrally down through the filter 2 and the bottom end of which includes generally U-shaped upper and lower parts 19, 20 which are bent outwards in mutually opposite directions, of which parts the lower part 20 is intended to grip around the stirrup- shaped handle 16 in the illustrated fashion and therewith hold the upper end of the filter 2 pressed against the flange 8. The upper, curved part 19 functions as a handle for urging 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 cap 10, so as to enable the filter 2 to be removed from the casing 3 and from the filter housing 1.

The filter housing 1 and/or the inner casing 3 may conve¬ niently have a spherical shape, thereby achieving advantages with respect to mechanical strength and with respect to liquid flow through the arrangement. The combined area of the filter-end will preferably be equally as large as the area of the inlet 4 and also roughly equal to the area of the outlet 5. This will result in a relatively low pressure drop across the filter arrangement as the liquid flows in through the inlet 4, along the inside of the filter housing 1 and the outside of the inner casing 3 to and through the openings 6, 7 and from there into the filter 2, wherefrom the liquid exits through the filter wall while extracting solid parti¬ cles from said liquid, and leaves through the outlet 5. Because liquid flows into the cylindrical filter 2 from both ends thereof, the whole of the filtering surface will be utilized generally uniformly, and the area of the filter

surface can be increased or decreased with relatively small affect on the outer dimensions on the filter arrangement. In the illustrated, preferred orientation of the filter arrange¬ ment, solid particles carried by the liquid are able to fall straight down into the bottom pipe stub 9 and are also extracted from the liquid at the filter surface and fall from said surface down into said pipe stub 9, from which the particles can be removed through the opening 15 or from the filter housing after removing the cap 10. It is also possible to reverse the direction of flow through the filter arrange¬ ment, although this is less favourable because the separated particles would collect within the inner casing 3. On the other hand, short duration reversal of the flow direction may be favourable, since this would enable particles that had fastened on the inside of the filter 2 to be released therefrom and therewith fall down into the pipe stub 9.

In the filter arrangement embodiment shown in Figs. 4 and 5, the filter housing 1 and the inner casing 3 have a configura- tion different to that of the Figs. 1-3 embodiment. For instance, the screen housing 1 is generally cylindrical and has an arched upper part. The inner casing 3 is also cylin¬ drical and is open at both ends. The inner casing 3 is positioned excentrically in the filter housing 1, more specifically such that the liquid will flow throughout the whole of the space between the housing 1 and the casing 3 at essentially the same rate of flow. The arrangement includes several tubular filters 2A, and the open ends of the filters are fitted in circular end plates 21, 22 which are provided with corresponding openings 6A, 7A and which are firmly connected to the filters 2A in sealing abutment with the inside of the cylindrical inner casing 3. The assembly comprised of the filters 2A and the end plates 21, 22 is provided with a handle 16 and is held removably in position in the inner casing 3 by virtue of the handle 16 resting against the inner surface of a bottom cap 10 removably connected to the filter housing 1. The cap is provided

centrally thereof with a cleaning opening that is closed by a threaded plug 23. Remaining components of the arrangement shown in Figs. 4 and 5 have been identified by the same reference signs as those used to identify corresponding components of the embodiment shown in Figs. 1-3 and will not be described in detail here.

The use of a plurality of tubular filters 2A enables the total filter area to be increased without increasing the volume of the filter assembly. The particles extracted from the liquid flowing through the filter arrangement collect essentially on the removable bottom 10 of the filter housing 1. The bottom part of the filter housing 1 forms a bottom pipe stub corresponding to the pipe stub 9 in Figs. 1-3.

Figs. 6 and 7 illustrate an embodiment in which a filter arrangement that corresponds in all essentials with the filter arrangement shown in Figs. 1-3 is combined with a gas separator. Such a gas separator can be used advantageously in a liquid circulating system, since the occurrence of gas, e.g. air in systems that operate with water-carried heat, are liable to lower efficiency and cause the occurrence of cavitations in circulation pumps. The gas separator and the filter arrangement include a common outer casing IA in the form of a horizontal cylinder having arched or curved ends and separated by a transverse partition wall 24. The gas separator has an inlet 25 and closable top and bottom pipe stubs 26, 27 through which collected gas and collected solid particles or sludge can be removed when so required. Extend- ing centrally through the interior of the gas separator between the inlet 25 and the partition wall 24 is a pipe 28 whose upper part is apertured to a large extent, as shown at 29, and the downstream end 30 of which that passes through the partition wall 24 forms the filter arrangement inlet. Gas bubbles that accompany the liquid as it passes through the gas separator are able to depart upwardly from the pipe 28, through its apertured part 29, so as to collect finally in

the upper part of the gas separator. Solid particles can also be separated from the liquid to a certain extent, these particles being removed through the pipe stub 27. As will be best seen from Fig. 7, the desired flow pattern through the gas separator is promoted with the aid of wings or baffles 31. The liquid entering the filter arrangement through the pipe end 30 is filtered in the manner described with refer¬ ence to Figs. 1-3.

The embodiment illustrated in Fig. 8 differs from the embodiment illustrated in Figs. 6 and 7 solely by virtue of the filter arrangement being located forwardly of the gas separator built together therewith. The liquid filtered or screened in the filter arrangement departs through the filter housing outlet, from which it passes in through the end 30 of the partially apertured pipe 28 and leaves the gas separator through the pipe stub 25.

It will be understood that the invention is not restricted to the aforedescribed and illustrated exemplifying embodi¬ ments thereof and that the invention can be applied in practice in any desired manner within the scope of the inventive concept defined in the following Claims.