TECHNICAL FIELD

The invention relates to a cylindrical air filter comprising filter media enclosed between an inner air permeable cylindrical wall and an outer cylindrical wall and at least one air tight end plate, sealing the space between cylindrical walls of the filter in an end distal from an inlet side of the filter.

BACKGROUND OF THE INVENTION

Air filter are used in many environments where the air can contain dangerous particles. One example is air filters in nuclear plants in which radioactive particles are captured in the filter media of the filters. When the amount of particles captured in the filter media reaches a certain level, the used filter has to be substituted by a new fresh filter. The used filter is then placed in a bin or container for radioactive waste and either stored at the nuclear plant or transported in the bin to a storage facility. Due to the regulations regarding radioactive waste, such bins are very expensive.

The object of the present invention is to construct an air filter, which improves the handling of used filters so that the number of bins for storage can be reduced.

SUMMARY OF THE INVENTION

This objective is accomplished by a cylindrical air filter comprising filter media enclosed between an inner air permeable cylindrical wall and an outer cylindrical wall and at least one air tight end plate, sealing the space between cylindrical walls of the filter in an end distal from an inlet side of the filter , characterised in that the filter comprises at least two cylindrical filter bodies having inner and outer walls between which filter media is enclosed, said filter bodies being displacably connected to each other. By such a construction of a cylindrical air filter, a cylindrical air filter comprising two such filter bodies can be compacted to half the size by displacing one of the filter bodies into the inner space of the other filter body which mean that two such compacted air filters can be disposed in a bin designed for one full sized air filter.

In a preferred embodiment, the at least two cylindrical filter bodies are telescopically displaceable in relation to each other. When the filter bodies are in an extended state, the diameters of the at least two cylindrical filter bodies decrease in a direction from the inlet side of the filter to the opposite end thereof , whereby a filter body of said at least two cylindrical filter bodies is telescopically displaceable into the cylindrical space between the inner wall of an adjacent of the at least two cylindrical filter bodies, said adjacent filter body being closer to the inlet side of the filter when the filter bodies are in an extended state. A gasket or other sealing means is preferably disposed between the outer wall of each cylindrical filter body, which is telescopically displaceable into the cylindrical space between the inner wall of an adjacent filter body, and the inner wall of said adjacent filter body. A releasable locking device locking the displacable filter bodies in an extended state is preferably disposed between the outer wall of each cylindrical filter body, which is telescopically displaceable into the cylindrical space between the inner wall of an adjacent filter body, and the inner wall of said adjacent filter body.

In a second preferred embodiment, the filter media enclosed between the inner and outer cylindrical walls is compressible and wherein one of the at least two filter bodies is insertable between the inner and outer walls of an adjacent of the at least two filter bodies, whereby the filter media enclosed between the inner and outer walls of said filter bodies are compressed during a such insertion.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described with reference to the enclosed figures, of which;

fig. 1 schematically discloses a partially sectioned side view of an air filter according to a first preferred embodiment of the invention in its extended state,

fig. 2 shows the air filter according to figure 1 in a compacted state, and

figs. 3 and 4 schematically discloses similar views as figure 1 and 2 of an air filter according to a second preferred embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

In figures 1 and 2, a first preferred embodiment of a cylindrical air filter 1 is schematically shown. The filter 1 has an open inlet side 2 allowing air from for example a ventilation duct (not shown) to flow into the filter 1 in an axial direction. The air filter 1 an inner cylindrical wall 3 and an outer cylindrical wall 4 between which a filter medium 5, for example consisting of pleated filtration paper, is enclosed. The end of filter 1 opposite to the inlet end is closed by an end plate 6. The cylindrical walls of the filter are air permeable so that air flowing into the inner space of the filter can radially pass through the filter medium 5, as indicated by arrows in figure 1. The cylindrical walls 3,4 can consist of perforated walls, as indicated in the figures, but other forms of air permeable walls, such as walls constructed from net-shaped material, could be used as well.

According to the invention, the inner wall 3 and the outer wall 4 are made of two separate cylindrical wall parts 7,8 and 9,10, respectively. The diameter of the cylindrical inner wall part 8 located distal from the inlet side of air filter 1 is larger that the diameter of the inner wall part 7 proximal to the inlet side 2 of filter 1 and the diameter of the outer cylindrical wall part 10 located distal from the inlet side of air filter 1 is smaller than the diameter of the outer cylindrical wall part 9 proximal to the inlet side 2 of filter 1. Thereby the filter body 11 distal from the inlet side 2 of the filter 1 and consisting of cylindrical wall parts 8,10, end plate 6 and the portion of the filter medium 5 enclosed between wall parts 8,10 is telescopically insertable into the filter body 12 proximal to the inlet side 2. During the insertion of filter body 11 into filter body 12, the filter medium 5 is compressed.

The dimensions of the diameters of the cylindrical walls 7- 10 of the filter bodies 11,12 are chosen so that the upper ends of wall parts 8,10, as seen in figure 1, abut the insides of wall parts 7,9. The insides of the wall parts 7-10 are the sides proximate to the filter medium.

If the rigidity of the filter medium 5 is large enough to withstand forces acting on the filter 1 during handling and transport thereof and the forces from the air flowing through the filter 1 during use thereof, the filter medium can be connected to the walls 7,8 and or 9,10 by a releasable connection, such as a glue seam or the like, in order to ensure that the air filter 1 will remain in the extended state shown in figure 1 when subjected to the forces mentioned above. Alternatively, the distal end of the walls 7,9 of filter body 12 can be releasably connected to the proximate end of the walls 8,10 of filter body 11 for example with the aid of glue. Said ends of filter bodies 11,12 could instead be frictionally connected to each other.

When a certain amount of particles has been captured in the filter medium 5, air filter 1 has to be substituted by a fresh one. Then the filter body 11 is pushed into filter body 12 with a force large enough for breaking the possible releasable connection between these two filter bodies and for compressing the filter medium 5. A filter 1 compacted in such a way is schematically shown in figure 2. The filter bodies can be so configured that a compacted filter will only take up about half the volume of a filter having the filter bodies in an extended state.

In the embodiment shown in figure 1 and 2, filter body 11 is insertable between the walls of filter body 12. It is of course possible to instead dimension the filter bodies so that the body proximate to the inlet side of the filter is insertable into the body distal to the inlet side of the filter. Moreover, in the shown embodiment both the inner and outer walls of filter body 11 are abutting the inside of the walls of filter body 12 but one of the walls of the distal filter body can instead abut the outside of the proximal filter body.

In figures 3 and 4 an air filter 13 according to a second embodiment is schematically shown in views similar to figures 1 and 2. The filter 13 includes two filter bodies 14,15. The main difference between this embodiment and the embodiment described with reference to figures 1 and 2 is that the filter body 15 distal from the inlet side 16 of filter 13 is telescopically insertable into the inner space of filter body 14, i.e. the space delimited by the inner wall 17 of filter body 14. Also in this embodiment the filter bodies 14,15 comprise an inner cylindrical wall 17 and 18, respectively, and an outer cylindrical wall 19 and 20, respectively, between which filter media 21 and 22, respectively are enclosed. An annular end plate 23 seals the annular space between the inner and outer cylindrical walls 17,19 at the end of filter body 14 distal from the inlet side 16 of the filter 13. The annular space between the inner and outer walls 18,20 of filter body 15 is at the end of filter body 15 proximate to the inlet side of filter 13 sealed by an annular end plate 24. The end of filter body 15 distal from the inlet side of the filter is sealed by an end plate 25 sealing the annular space between the inner and outer walls 18,20 as well as the inner space of this filter body.

An annular gasket 26 is disposed between the inner wall 17 of the filter body 14 and the outer wall 20 of filter body 15 in order to ensure that air can not escape from filter 13 without having passed through the filter media 21,22 enclosed between the walls of filter bodies 14,15.

A releasable locking device 27 is preferably disposed on the annular end plate 24 of filter body 15. Such a locking device holds the filter bodies 14,15 in an extended state during storing, transporting, mounting and use of filter 13. Such a locking device can consist of one or more resilient tongues, resting in grooves in the extended state of the filter bodies 14,15. Said grooves can have a decreasing depth in a circumferential direction so that the resilient tongues can be brought from the locking state by rotation of the filter body 15 in relation to filter body 14. However, other types of locking devices including breakable connections can be used.

A separate locking device is preferred but not absolutely necessary. The gasket 26 can be designed to frictionally hold the filter bodies in an extended state during normal handling and use of filter 13. When the filter 13 is to be substituted by a fresh one, the locking device 27 is unlocked and filter body 15 is inserted into the inner space of filter body 14 as is schematically shown in figure 4. In contrast to the embodiment according to figures 1 and 2, the filter media will not be compressed by the insertion of the filter body 15 into filter body 14. Thereby there is no risk that captured particles will be spread from the filter media due compression or break thereof which might be the case in the embodiment according to figures 1 and 2. If the particles captured in the filter media are of very dangerous nature, a filter 13 according to the embodiment described with reference to figures 3 and 4 are preferably chosen. Also in this embodiment the filter bodies are so configured that a compacted filter takes up about half the space as an extended filter.

The cylindrical walls of the filter bodies is preferably made of metal, especially if the filters are to be used in a nuclear plant. For other uses plastic materials or other wall materials known to be used in air filters can be used.

The filter medium is preferably filtration paper. The filters are preferably of HEPA (High Effeciency Particle Arrestor) quality.

The described embodiments can be modified without leaving the scope of invention. For example, the filters can contain more than two filter bodies telescopically coupled to each other. Furthermore, the filter bodies can have circular, rectangular, square, triangular and other cross-sections. For some uses the filter bodies in the embodiment according to figures 3 and 4 can be inserted into each other during storing and transport and be extended just before use. The scope of invention shall therefore only be limited by the content of the enclosed patent claims.