The filter systems which are typically used today for the cleaning of media, such as the lubricating oil in engines driving e. g. electric generators on ships, are manufactured as an integrated unit, where the active filter me- dium is encapsulated in a protective steel jacket which simply cannot be separated from the filter medium.

When the filter medium is to be replaced after use, this therefore means that also the protective steel jacket has to be replaced.

Within the maritime transport business, it was previously so that, when worn, the filters for cleaning the engine lubricating oils were frequently thrown overboard when the ship was on the open sea. However, as a result of the internationally enhanced awareness of the environment several countries have now adopted regulations for the handling of the used filter units. Now, the standard is thus that filters are registered and may not be thrown overboard after use, but have to handed over to the regional envi- ronmental authorities for disposal. Normally, the ship owners are to pay the costs of the disposal of the exchanged filter units.

It is known from WO 99/64133 to manufacture filter systems which are composed of modules. These known filter modules are assembled using special coupling elements which add to the costs of the finished product and make exchange and assembly cumbersome and are relatively expen- sive to manufacture.

Accordingly, an object of the invention is to manufacture a filter system where all the metallic parts may be used again, and where the active filter module, which is to be exchanged at intervals, may be separated from the rest of the filter system in a simple manner.

The object of the invention is achieved by a filter system of the type defined in the introductory portion of claim 1, which is characterized in that the filter modules have flanges at each end which are constructed such that an end flange from one module may engage an end flange on another module, and that the filter modules are clamped together at their outer ends with two outer flanges, said outer flanges being adapted to engage the flanges of the outer filter modules.

Hereby, the filter modules may be released from the rest of the filter system merely by loosening the outer flanges.

A particularly expedient way of loosening the outer flanges from the rest of the filter system is advantageously carried out in that, as stated in claim 2, the clamping is established with a central through shaft which extends through the outer flanges, and that the central shaft has clamping means at its ends.

To ensure a sufficient seal between the filter modules after the clamping, it is an advantage if the clamping is carried out as stated in claim 3, more particularly in that the end flange at one end of a filter module is formed by a truncated cone provided at the outer side of the filter module or as a wall having a slightly inwardly inclined outer side, while the end flange at the other end at the outer side is formed as a circular wall, and so that the outer side of the truncated cone or the wall may engage the inner side of the cir- cular wall.

Hereby, a press fit is provided, ensuring a good and sufficient seal between the filter modules.

When, as stated in claim 5, the filter modules are enclosed by a perforated outer protective jacket in the form of a steel pipe, it is ensured that the filter modules do not collapse in use when their outer sides are subject to great pressures.

Additionally, it is an advantage if, as stated in claim 6, a perforated inner protective jacket in the form of a steel pipe is provided along the inner side of the filter modules, and, as stated in claim 7, a steel net is arranged along the inner side of the inner protective jacket, said net having a mesh size which allows larger particles to pass than the filter modules allow, as the inner protective jacket will stiffen the filter modules, while the filter steel net will serve as a safety filter if one or more of the filter modules should col- lapse.

When, as stated in claim 8, the filter modules are made of combustible materials, where the end flanges are made of a plastics material, such as polyamide or teflon, it is possible to incinerate the filter modules in waste combustion furnaces, such as e. g. the so-called incinerators which are fre- quently provided on modern ships.

Thus, it is clear that filter systems composed of filter modules according to the present invention are easy to handle, environmentally acceptable and also economically advantageous for the users, who also avoid having to pay for the disposal of the worn filters.

Additional expedient embodiments of the invention are defined in claims 4 and 9.

The invention will now be explained with reference to the embodiment shown in the drawing, in which fig. 1 shows a filter system having filter modules according to the invention, partly in section, fig. 2 shows two filter modules in perspective, while fig. 3 shows components incorporated in the assembly of a filter system according to the invention.

In fig. 1, a filter system according to the invention is generally designated 1.

Here, the filter system consists of three filter modules, two of which are designated 2.

The filter modules may also be composed of a pleated paper material which is terminated by end flanges, cf. also fig. 2, as will be explained later.

As mentioned, three filter modules are assembled in fig. 3 in that adjacent flanges are clamped together by means of a central through shaft 9, which has a nut 7,8 at its ends which may be clamped against two outer flanges 14,15, which each engage end flanges of their respective filter modules 2.

A protective pipe 6, which may be a perforated steel pipe, is arranged along the outer side of the filter modules.

An inner protective pipe is arranged along the inner side of the filter mod- ules 2, and this protective pipe, too, may be constructed as a perforated steel pipe on whose inner side a steel net may be arranged, having a mesh size that allows larger particles to pass than the pleated paper of the filter modules allows.

A hole 4 is provided at one of the outer flanges 15, while a safety valve (not shown) is arranged in the other outer flange.

Before explaining more fully how the filter modules are composed, it will first be explained how the filter system operates in use.

The medium to be cleaned is transported in the direction of the arrow 3 in- wards toward the filter modules 2 where the pleated paper ensures that impurities of a certain particle size do not pass.

The cleaned medium passes through the inner protective pipe and leaves the filter system through the shown hole 4 in the one outer flange 15.

When the filter module has been in operation for a given period, the filter system is separated in that the nuts 7,8 are loosened, and the outer flange or both outer flanges are removed, following which the filter modules are replaced by new ones.

The used modules, which are made of combustible materials, are sent to a combustion facility in which the filters with impurities are incinerated in an environmentally acceptable way.

In the use of such a filter system it is extremely important that there is a good seal between the individual filter modules, so that the entire medium to be cleaned passes through the pleated paper of the filter modules and not through the adjacent flanges of the filter modules.

To ensure that there is a sufficiently tight connection between the end flanges of the modules, they are constructed such that an end flange of a module may be pushed together with another end flange of another mod- ule. This is done in that along the outer side of a filter module there is pro-

vided a frustoconical wall 11 which may engage a circular wall 11 provided in an adjacent filter module, and so that the inner diameter of the circular wall has a size which just allows the outer side of the frustoconical wall to be pressed against the inner side of the circular wall when the filter mod- ules are clamped together, Instead of a frustoconical wall, it is possible to provide a wall having an outer side inclined slightly inwards in a direction toward the centre of the filter module.

Additionally, the end flanges, at their inner sides, of the filter modules are formed with a circular wall 12. The interior of this circular wall forms part of a U-shaped recess which serves to attach the pleated paper of the filter module, e. g. using a hardening mass which is introduced into the U-shaped recess together with the pleated paper.

In general, it is intended that the circular walls at the end flanges do not adjoin each other completely after clamping, but form a gap 13 between them, so that no pressure can be generated in the cavity 16 which is de- fined by the inner and outer walls of the end flanges, with the consequent risk of leakages being created at the outer walls.

In the event that a filter module gets inoperative for some reason and al- lows particles to pass, the filter arranged on the inner side of the inner pro- tective pipe will absorb most of these impurities and be clogged shortly af- terwards, so that it will quickly be detected that there is a defect in the filter system.

Also, the safety valve (not shown) in the outer flange 14 will open if the hole 4 is closed for some reason, or, altogether, if there is an interruption of flow after the hole.

Fig. 3 shows the most important parts of the parts incorporated in the filter system according to the invention, in a disassembled state. These parts are a filter module 2, the outer protective pipe 6, the central shaft 9 with the outer flange 14 and the inner protective pipe 5.