TECHNICAL FIELD

The present invention relates to a filter insert for sewage vent pipes according to the preamble of claim 1 .

BACKGROUND ART

Ventilation systems for sewage systems normally comprise an outlet pipe, also called ventilation pipe or vent pipe, which is located outdoors for expelling the air and gases from the sewage. The vent pipe is generally provided with a filter for purifying the outlet air from contamination or odour. This is especially the case in ventilation systems for city waste water networks or sewage, in which the odour from the expelled air could disturb neighbouring residential areas.

A known filter unit for sewage vent pipes comprises a filter housing and an adaptor. In the known arrangement, the adaptor is fixed to the end of the vent pipe and the filter is attached to the adaptor. The filter housing is thereby positioned above the end opening of the vent pipe and thus extends above the vent pipe.

A problem associated with this known filter unit is that it is exposed to external forces, such as snow, rain, debris or strong winds which may clog or damage the filter. The overall lifetime of the filter is therefore reduced. A further problem is that individually dimensioned adaptors must be provided for sewage vent pipes of different dimensions. This increases the manufacturing cost of the filter unit. The arrangement of the filter and the adaptor makes it further cumbersome to change the filter since the adaptor must be removed before the filter can be exchanged.

Thus, an object of the present invention is to achieve a cost effective filter unit that is easy to handle and which has a long lifetime. SUMMARY OF THE INVENTION

According to the invention this object is achieved by a filter unit for sewage vent pipes, said filter unit comprising a filter housing comprising a filter medium for purifying sewage gases, said filter housing comprising a closed end portion and an upper portion comprising an opening for letting purified air out of the filter housing, characterized in that the filter housing is configured to fit inside a sewage vent pipe, wherein said filter unit further comprises a support means that is attached to the upper portion of the filter housing, said support means comprising a ring-shaped portion that protrudes a predetermined distance over the filter housing, so that when the filter housing is inserted into a sewage vent pipe, the lower surface of said ring-shaped portion is supported on the end surface of the sewage vent pipe. Due to the configuration of the filter housing and the ring-shaped portion of the support means the filter housing can be lowered into a sewage vent pipe and is held in position there by the support means that rests on the end surface of sewage vent pipe. The wall of the sewage pipe thereby protects the filter housing from external forces such as rain or debris. A further advantage is that the filter unit is held in place in the sewage vent pipe by its own weight. Thus, no additional clamps are needed.

The filter unit can be used in all existing sewage vent pipes, provided that the ring-shaped portion is manufactured with a diameter that is larger than the outer diameter of all standard sewage vent pipes. The filter unit can therefore be produced at low cost since no extra adaptors are necessary.

It is easy to change the filter medium in the filter unit since it is only necessary to lift the filter unit out of the vent pipe, exchange the filter medium and replace the filter unit in the vent pipe again. In the same manner it is easy to exchange the entire filter unit. A sealing element may be arranged on the lower surface of the ring-shaped portion. The sealing element provides for an air tight seal between the filter unit and the vent pipe. Ideally, the compressibility and the thickness of the sealing element is selected such that, when the filter housing is inserted into a sewage vent pipe, an air-tight seal against the end surface of the sewage vent pipe is achieved by the weight of the filter unit acting on said sealing element. According to an alternative, the sealing element is manufactured from polyurethane foam. This material provides for effective sealing and is easy to apply to the support means by spraying.

According to one embodiment, the lower surface of the ring-shaped portion comprises at least one circular groove for receiving an end portion of a sewage vent pipe. The filter unit can thereby be securely supported on the end of the sewage vent pipe and is effectively prevented from sliding of the sewage vent pipe. Preferably, filter unit comprises several grooves arranged on predetermined distances from the center of the ring-shaped portion. The same filter unit can thereby be used on sewage vent pipes of different diameter.

Preferably, the grooves are formed between walls, extending from the lower surface of the ring-shaped portion.

The sealing element is preferably arranged in said at least one groove.

According to an alternative the filter unit comprises a weather cover.

The weather cover may be detachable arranged on the support means. According to an alternative, the weather cover is integrated with the support means.

According to one alternative, the support means is detachable attached to the filter housing.

The support means and the filter housing may each comprises a threaded portion, so that the support means can be screwed onto the filter housing. This provides for an economically favorable filter unit since the same support means can be used several times whereby only the filter housing or filter medium need to be exchanged.

According to a further alternative the support means is formed integrally with the filter housing. Such a filter unit is cost effective since it is inexpensive to manufacture in one step.

The support means may for example be glued to the filter housing. This is an inexpensive way of attaching the filter housing to the support means. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates schematically a prior-art filter unit that is mounted on top of a sewage vent pipe.

Figure 2 illustrates schematically a cross-section of a filter unit according to a first preferred embodiment of the invention.

Figure 3 illustrates schematically a cross-section of a filter unit according to a second embodiment of the invention.

Figure 4 illustrates in a view from below the support means of the filter unit of the second embodiment of the invention. Figure 5 illustrates schematically a filter unit according to the first embodiment of the invention inserted into a sewage vent pipe.

DETAILED DESCRIPTION

Figure 1 shows schematically a prior-art filter unit 100 comprising an adaptor 101 and a filter 102. The filter unit is mounted on the end of a sewage vent pipe 103 through which air 107 is vented out from a sewage well 104. The filter 102 is attached to the end of the vent pipe 103 by the adaptor 101 that is fixed to the vent pipe 103. The filter 102 thereby extends above the vent pipe 103. On top of the filter is a roof shaped hat 105 mounted to protect the filter from rain, snow etc.

Figure 2 shows a first embodiment of a filter unit 1 according to the invention in cross-section. The filter unit 1 comprises a hollow cylindrical filter housing 10 that comprises an elongated cylindrical central portion 1 1 , an upper portion 12 and a lower portion 13. An opening 14 is provided in the upper portion 12 of the filter housing. The lower portion 13 is closed by an end wall 15. The outer diameter of the filter housing 10 is less than the inner diameter of the sewage vent pipe that the filter unit should be installed in. Preferably, the outer diameter of the filter unit is at 0,5 cm less than the inner diameter of the sewage vent pipe so that when the filter housing is lowered into a sewage vent pipe, a gap is formed between the filter housing and the inner wall of the sewage vent pipe. The length of the filter housing depends on the amount of sewage gas that shall be filtered. If a high filtering capacity is needed a long filter housing is provided.

The filter housing 10 further comprises a filter medium (not shown) suitable for absorbing contamination from the air from the sewage. According to one alternative, the filter medium is granules and/or pellets of active carbon, zeolites or ion-exchanger material. The granules are typically of a diameter of 2-3 mm. In this case the elongated cylindrical portion 1 1 of the filter housing comprises an outer wall 17 and an inner wall 18 that are perforated with small holes 16, of 1 -2 mm in diameter. The walls are arranged at a distance from each other, so that a gap of typically 2 cm is formed between the walls. The gap between the walls is filled with the granular filter medium. According to a second alternative (not shown), the filter housing 10 is manufactured from sintered active carbon i.e. either or both of the cylindrical portion 1 1 and the end wall 15 are manufactured from sintered active carbon. According to a further alternative (not shown), the elongated portion 1 1 is manufactured from pleatable carbon medium. This material can e.g. comprise outer fibre layers and an intermediate active carbon layer and is pleated so that a large surface is achieved. It is also possible that the pleatable carbon medium comprises active carbon granules that are held in place by fibre layers. In this case ribs could be provided in the pleatable carbon medium to reinforce the filter housing.

The filter unit 1 further comprises a support means 30 having a general flat circular form and comprising a central opening 35. The support means 30 is attached to the upper portion 12 of the filter housing 10 so that the opening 35 in the support means 30 is concentric with the opening 14 in the filter housing. According to one alternative, the support means 30 is integrated with the filter housing, i.e. the support means and the filter housing is formed in one piece. According to a second alternative, the support means 30 is glued to the upper portion of the of the filter housing. According to a further alternative, the support means 30 comprises attachment means that extends around the opening 35 so that the support means 30 can be attached to the upper portion 12 of the filter housing. For example the attachment means comprises a cylindrical portion 32 that extends vertically upwards an surrounds the central opening 35 in the support means 30. The vertical cylindrical portion 32 may be provided with an inner thread 33. In this case the upper portion 12 of the filter housing is provided with a corresponding outer thread 19 so that the filter housing and the support means can be screwed together. However, other types of attachment means are possible in both the support means and in the filter housing. For example, latches or bayonet fittings. The support means 30 further comprises a flat ring-shaped portion 34 that extends horizontally in a direction away from the central opening 35. The ring-shaped portion 34 is configured, i.e. its width is dimensioned, so that the ring shaped portion protrudes a distance over the cylindrical elongated portion 1 1 of the filter housing 2. The protruding distance should be dimensioned so that the distance from the centre of the support means 30 to the outer edge 37 of the ring-shaped portion 34 is at least equal to the outer diameter of the sewage vent pipe that the filter unit should be installed in. More preferably, the protruding distance should be dimensioned so that the distance from the centre of the support means to the outer edge of the ring-shaped portion 34 is greater than the outer diameter of the sewage vent pipe that the filter unit should be installed in. Preferably, the ring-shaped portion protrudes a distance that is greater than the outer diameter of all standard types of sewage vent pipes.

The support means and rigid parts of the filter housing, such as walls and top and bottom parts, are preferably manufactured from a plastic material such as Polyethylene, Polypropene, Polystyrene or Acrylonitrile Butadiene Styrene (ABS).

The support means 30 may further comprise at least one sealing element (not shown) that is arranged on the lower surface of the ring-shaped portion 30. Typically, the sealing element covers the whole area of the lower surface of the ring-shaped portion 30. However, the sealing element may also be ring-shaped and be arranged on a predetermined distance from the centre of the support means. The predetermined distance corresponds to the diameter of the sewage vent pipe that the filter unit shall be installed in.

The sealing element is configured such that when the filter unit is lowered into the sewage vent pipe, an air-tight seal is achieved between the ring- shaped portion 34 and the end surface of the vent pipe, by the weight of the filter unit acting on the seal. To achieve this it is important to provide a sealing element which has the right compressibility, softness and thickness with respect to the weight of the filter unit. It is appreciated that these parameters are determined by the skilled person in order to achieve an air tight seal. Preferably, the sealing material is manufactured from polyurethane foam, silicone, polyester, polyethene or EPDM.

A second embodiment of the filter unit according to the invention is shown in figures 3. In this embodiment the filter housing 10' is identical to the filter housing 10 described in connection with the first embodiment. The filter unit 1 ' comprises a support means 30' similar to the support means 30 of the first embodiment. The support means 30' comprises a protruding ring-shaped portion 34'. The lower surface of the ring-shaped protruding portion 34', i.e. the surface that is directed towards the lower portion 13' of the filter housing, comprises one or several grooves 38'. The grooves 38' are ring-shaped and run concentrically with opening 35' in the support means 30', (see figure 4). The grooves 38' are formed by walls 36' that extend vertically from the lower surface of the ring-shaped protruding portion 34' in a direction towards the end portion 13' of the filter housing. The height of the walls are dimensioned such that the filter unit is kept in place without having the possibility to slide of the sewage vent pipe. Preferably the height is at least 10 mm. The width of the grooves 38', i.e. the distance between two adjacent walls 36' should be greater than the wall thickness of the sewage vent pipe and may for example be at lest 10 mm. The grooves are arranged on predetermined distances from the centre of the support means 30'. The distances correspond to the outer diameter of the sewage vent pipe that the filter unit should be installed in. Preferably the distances correspond to outer diameters of different standard sewage vent pipes. For example, going from a standard size of 100 mm to next standard size of 1 10 mm. A sealing element (not shown), as described under the first embodiment may be arranged on the lower side of the ring-shaped element. The sealing element is arranged in the grooves, i.e. between two adjacent walls. Preferably, the sealing element is polyurethane foam that is sprayed into the grooves.

The filter unit may further comprise a weather cover, also called weather cap, which prevents snow, rain or debris form falling into the filter housing through the opening 14. Figure 3 shows a filter unit according to the second embodiment of the invention that is provided with a weather cover 40'. However, a similar weather cover may also be provided in the filter unit according to the first embodiment.

The weather cover 40' is dome-shaped, however other shapes are also possible, for example pointed shapes, such as a roof shapes or pyramid shapes. The weather cover is attached to the outer edge 37' of the support means 30'. The weather cover is attached such that gaps 41 ' are formed between the weather cover and the support means 30' so that air can exit from the filter unit. The weather cover 40' may be integrated in the support means 30', e.g. formed together with the support means. The weather cover 40' and the support means 30' may also comprise corresponding attachment means (not shown) so that the weather cover can be attached to and removed from the support means. For example, the weather cover may comprise latches and the support means may comprise corresponding grooves so that the weather cover can be snapped on to the support means. It is also possible to provide corresponding threads in the weather cover and the support means so that the weather cover can be screwed onto the support means. Figure 5 shows the inventive filter unit 1 lowered into a ventilation pipe 50 of a sewage system. The protruding ring-shaped portion 34 of the support means 30 rests on the end surfaces of the vent pipe 50 and the filter housing 10 extends within the vent pipe so that it is surrounded by the vent pipe. The filter housing is thereby protected by the walls of the vent pipe. As can be seen in figure 3, a gap is formed between the filter housing and the sewage vent pipe. Air 60 that is rising through the vent pipe 50 enters through the walls of the tubular filter housing 10 and is filtered by contact with the filter medium in the filter housing. The filtered air exits through the upper opening 14 of the filter housing 10.

Although particular embodiments have been disclosed this has been done for purpose of illustration only and is not intended to be limiting. Features of the enclosed embodiments may be combined. In particular it is contemplated by the inventor that various substitutions, alterations and modifications may be made within the scope of the invention.