FIELD OF THE DISCLOSURE

The present disclosure relates to a liquid filtering apparatus, as described in the preamble of independent Claim 1 . The present disclosure also concerns a key and a filter medium element, as described in the preamble of independent Claims 20 and 27, respectively. Furthermore, the present disclosure also relates to a method of operating and servicing a liquid filtering apparatus, as described in the preamble of independent Claims 33 and 34, respectively.

BACKGROUND OF THE DISCLOSURE

In a conventional liquid filtering apparatus of the type concerned by the present disclosure, normal operation follows an operation cycle, in which filter material is first fed into a filter chamber in which in filtrate is separated from the solids content of the filter material by the filter medium. As a result, a filter cake of solids is formed within the filter chamber, while filtrate flows through the filter medium. The filtrate separated from the filter material is collected for possible further processing with a drainage arrangement. After the filter cake effectively fills the filter chamber, no more filter material can be fed. At this stage, compression is typically applied on the filter cake so as to extract residual filtrate therefrom, which is then also collected by the drainage arrangement. Finally, no more filtrate can feasibly be removed from the filter cake, and the cake is discharged from the filter chamber by removing it therefrom. Additional steps, such dry blowing and/or filter cake washing may precede filter cake discharge.

BRIEF DESCRIPTION OF THE DISCLOSURE

An object of the present disclosure is to facilitate maintenance of a liquid filtering apparatus of the type being gravitationally dischargeable of a filter cake via a bottom discharge opening, the filter chamber being immovable at least during discharge of the filter cake.

The objects of the disclosure are achieved by the liquid filtering apparatus, and a key, filter medium element, method for operating and method for servicing a liquid filtering apparatus, as characterized by the independent Claims 1 , 20, 27, 33 and 34, respectively.

The preferred embodiments of the disclosure are disclosed in the dependent claims. The disclosure is based on the idea of providing a filter medium element having a jacket with a closed circumference defining an inner space. This provides the advantage of not having to disassemble a filter chamber element 2 when replacing the filter media.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the disclosure will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Figs. 1 -5 exemplarily illustrate schematic variations of a liquid filtering apparatus according to the disclosure as a cut view;

Fig. 6 exemplarily illustrates a schematic cut view a liquid filtering apparatus according to the disclosure having several filter chamber elements;

Figs. 7-9 exemplarily illustrates various aspects of a key according to the disclosure;

Figs. 10-12 exemplarily illustrates various aspects of a filter medium element according to the disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

In the following, the term when in use is intended to describe the condition of an entity during a normal operation cycle of a liquid filtering apparatus. That is, during filter material feed, filter cake compression, filtrate drainage and filter cake discharge. In this context, service and maintenance procedures, such as replacing a filter medium, is not considered as a part of the normal operation cycle.

According to a first aspect of the disclosure, a liquid filtering apparatus 1 is provided. Such a liquid filtering apparatus 1 comprises at least one filter chamber element 2, within which an intermediate space is formed. Furthermore, a filter chamber 3 is formed within the intermediate space of the filter chamber element 2. The filter chamber 3 has a top feed opening 3a at a level above the filter chamber and bottom discharge opening 3b at a level below the filter chamber. The filter chamber 3 is gravitationally dischargeable of a filter cake via said bottom discharge opening 3. That is, a filter cake formed within the filter chamber 3 can be removed therefrom by letting the filter cake fall due to its own weight. Naturally, detaching the filter cake from the walls of the filter chamber 3 may be aided. It should be noted, that although the filter chamber needs to extend vertically, it does not need to be fully vertical, i.e. it may be inclined with respect to the vertical. Moreover, the filter chamber 3 itself is immovable at least during discharge of a filter cake. In other words, opposing walls of the filter chamber typically, but not necessarily, provided as adjacent filter plates 2', 2" do not need to be retracted away from each other to discharge the filter cake.

The liquid filtering apparatus 1 further comprises, in said intermediate space, a filter medium element 4. The filter medium element 4 comprises a jacket 4a, a feed opening 4b and discharge opening 4b. The jacket 4a has, when in use, a vertically extending closed circumference defining an inner space, at least laterally limiting the filter chamber 3. The feed opening 4b is arranged to operationally correspond with the top feed opening of the filter chamber for enabling filter material to be fed into the inner space. That is, filter material may be fed to the inner space of the filter medium element 4 through the top feed opening 3a and the feed opening 4b. Suitably, the feed opening 4b is arranged for being attachable to at least a portion of a key 5 so as to secure the filter medium element 4 to the liquid filtering apparatus 1 .

The discharge opening 4c is arranged to operationally correspond with the bottom discharge opening 3b for enabling a filter cake formed within the inner space to be discharged therefrom. That is, a filter cake may be discharged from the inner space of the filter medium element 4 through the bottom discharge opening 3b and the discharge opening 4c.

Providing the filter medium element 4 as a one having a jacket 4a as discussed above, enables the filter medium element 4 to be inserted and removed without disassembling the filter chamber element 2, as the filter media does not need to be clamped between filter plates for ensuring a sealed inner space into which the filter cake is formed, as conventionally has been done.

The liquid filtering apparatus further comprises, in connection with said filter chamber 3, a drainage arrangement 2a configured to receive filtrate filter chamber 3 through the filter medium element 4

Preferably, but not necessarily, the drainage arrangement 2a is configure to receive filtrate from at least two sides of the filter chamber 3 through the filter medium element 4, at least during filter material feed to the inner space of the filter chamber 3. This is advantageous for the filter cake formation and filter cake discharge in connection with a filter medium element 4 according to the disclosure. Particularly, draining filtrate from at least two sides ensures, that the filter cake is formed firm enough to be discharged gravitationally from the inner space having a closed circumference. The liquid filtering apparatus 1 further comprises, in connection with said filter chamber 3, a compression arrangement 2b configured to apply compression to the filter chamber 3 externally of the filter medium element 4, so as to extract residual filtrate from filter cake formed within the filter chamber

3. The drainage arrangement is further arranged to receive filtrate also during such extraction of residual filtrate, preferably from at least one side of the filter medium element

4, although receiving filtrate from at least two sides of the filter medium element 4 is envisaged. The compression arrangement further aids in the filter cake formation and discharge.

Suitably, the compression arrangement 2b may be further configured to apply compression to the filter chamber 3 from at least two sides thereof. That is, compression may be applied from two sides of the filter medium element 4 external of the filter chamber.

The liquid filtering apparatus may naturally be provided with other arrangements, such a filter material feeding arrangement configured to selectively feed filter material into the filter chamber, between within the filter medium element 4. Moreover, a discharge arrangement may be provided, configured to discharge a filter cake from each filter chamber. Such a discharge arrangement may suitable be also configure to selectively open and close the bottom discharge opening 3c.

In an embodiment according to the first aspect of the disclosure, the liquid filtering apparatus 1 further comprises, in connection with said filter chamber 3, a key 5 for securing the filter medium element 4 in place, and enclosing the filter chamber top feed opening 3a.

The key 5 comprises a head portion 5a and a stem portion 5b. The stem portion 5b extends from the head portion towards the filter chamber 3 so as to be at least partly received within the top feed opening 3a of the filter chamber 3. Preferably, but not necessarily, the head portion 5a is arranged to cover the top feed opening so as to enclose the top feed opening 3a.

The key 5 further comprises, within the head portion 5a, an internal fluid channel 5c in fluid communication with at least one hole 5d on the stem portion, so as to provide fluid communication between the internal channel 5c and the filter chamber 3 of the liquid filtering apparatus 1 . Using such a key 5 also facilitates inserting and removing a filter medium element 4 according to the disclosure, as it can be attached to and detach from the filter medium element 4 without disassembling the filter chamber element 2

The filter medium element 4 may be secured in place by being pressed between the key 5 and the remaining liquid filtering apparatus 1 , for example. Additionally, or alternatively, the filter medium element 4 may be affixed to the key itself, which in turn, is secured to the remaining liquid filtering apparatus 1 .

Preferably, but not necessarily, the stem portion 5b of the key 5 may have an at least partially increasing cross-sectional dimension towards the head portion. This provides an at least partly a wedge-shaped form, particularly advantageous for ensuring that the filter medium element 4 is secured, should it be pressed between the key 5 and the top feed opening 3a.

Preferably, but not necessarily, the internal fluid channel 5c may extend in a longitudinal direction of the key 5 along the head portion 5a. Moreover, a plurality of holes 5d may be provided along the stem portion 5b, spaced in a longitudinal direction of the key 5, so as to provide fluid communication between the internal channel 5c and the filter chamber 3 of the liquid filtering apparatus. In typical applications, that is when the key is arranged above the filter chamber, the longitudinal direction of the key 5 corresponds to the width direction of the filter chamber.

Preferably, but not necessarily, the key 5 may comprises a key feed connection 5e for receiving fluid into the internal channel, and a key discharge connection 5f for discharging fluid from the internal channel 5c. This enables a fluid flow through the internal fluid channel 5c, which is advantageous for flushing the internal fluid channel 5c from any particles blocking the said internal fluid channel 5c, or one or more holes 5d, for example. Such key feed connection 5e and key discharge connection 5f are suitably positioned opposite to each other in a longitudinal direction of the key 5, resulting in such a flushing flow extending over the whole length of the internal fluid channel 5c.

Preferably, but not necessarily, at least one hole 5d on the stem portion 5b of the key 5 has a cross-sectional dimension at least partially decreasing towards the internal fluid channel 5c. This effectively prevents particles blocking one or more holes 5d from being wedged within said hole 5d by the feed pressure pushing such a particle towards a narrowing cross section. Moreover, such construction of the hole 5d even facilitates release of blocking particles, as the feed pressure pushes blocking particles towards a wider cross section.

In a further embodiment of first aspect according to the disclosure, a sealing element 6 may be provided in connection with the top feed opening 3a, running along the inner circumference thereof. The sealing element may be configured such thatthe filter medium element 4 is pressed against said sealing element by the key 5, for example. Alternatively, or in addition, a sealing member may be provided to seal the interface between the stem portion 5b of the key 5 and the top feed opening 3a. It should be understood, that other sealing arrangement for sealing the interface between the key 5, top feed opening 3a and the filter medium element 4 may be used.

In another embodiment of the first aspect according to the disclosure, the liquid filtering apparatus is configured such that the filter medium element 4 is arranged to be receivable within the filter chamber 3 via the top feed opening 3a thereof. In other words, the dimensioning of the filter medium element 4 and the top feed opening are arranged such that the filter medium element 4 can be inserted into the filter chamber 3 through the top feed opening 3a. This also facilitates inserting and removing the filter medium element 4 without the need to disassemble the filter chamber element 2.

Preferably, but not necessarily, the filter medium element 4 may further comprises at least one flap 4d extending freely from the level of the feed opening 4b. In such a case, the flap 4d is suitably folded against a portion of the liquid filtering apparatus outside of and surrounding the top feed opening 3a of the filter chamber 3.

Moreover, the portion of the liquid filtering apparatus outside of and surrounding the top feed opening 3a of the respective filter chamber 3 may preferably, but not necessarily, comprise one or more projections 7. Respectively, the at least one flap 4d may further comprises one or more holes 4d' for receiving said at least one projection 7.

Preferably, but not necessarily, the filter medium element 4 comprises a first layer, such that the jacket 4a of the filter medium element 4 is formed by adjoining at least opposite sides of the first layer, thus defining the vertically extending closed circumference. In such a case, the feed opening 4a, discharge opening 4b, or both, are suitably formed of either or both, respectively, detached section of a side adjacent to the adjoined sides of the first layer.

Alternatively, the filter medium element may comprise a first layer 4' and second layer 4", such that the jacket 4a is formed by adjoining the first layer 4' and the second layer 4" together along respective opposite sides, thus defining the vertically extending closed circumference. In such a case the feed opening 4a, discharge opening 4b, or both are suitably formed from respective detached sections of the first and second layers.

Moreover, at least one flap 4d, as described above, may then be provided as a freely extending section of the first layer, second layer, or both, separated from the second layer, first layer, or each other, respectively. In a further embodiment of the first aspect according to the disclosure, the filter chamber 3 and the filter medium element 4 may preferably be configured such that a filter cake formed within the inner space thereof has a thickness of less than 15 cm, preferably 0,5- 15cm. In practise, the dimensioning of the filter chamber 3 and the filter medium element 4 may be dimensioned such that that the thickness of the inner space of the filter medium element 4 does not exceed the desired value even when filter material is fed into the filter chamber 3. In this respect, the term thickness should be understood as the smallest dimension of filter cake, inner space, or filter chamber 3. The basic concept of the disclosure does not, as such, restrict the shape of the filter chamber 3, although the thickness of the filter cake should not be too thick, in order to ensure proper filter cake formation, in turn, contributing to cake discharge. Preferably, but not necessarily, the filter chamber 3 is of a substantially flat planar shape, i.e. it has two other dimension (i.e. height and width) in another order of magnitude than the thickness.

Preferably, but not necessarily, the filter chamber 3 and the filter medium element 4 may be configured such that a filter cake formed within the inner space thereof of the filter chamber has a largest dimension (i.e. height or width) of at least 6 times greater than the thickness. Suitably, the largest dimension lies in the range of 1 -10m.

In still another embodiment of the first aspect according to the present disclosure, the filter chamber element 2 may be formed by a filter plate pack having adjacent, operationally aligned filter plates 2', 2'. In other words, the filter plates 2', 2" are placed one after another side by side so as to convey mechanical forces between each other. Moreover, the filter plates are 2', 2" arranged, when in use, immovable in contact with each other in the filter plate pack. Naturally, such filter plates 2', 2" may be detached from each other outside of the normal operation cycle, in connection with service and maintenance, for example. In yet a further embodiment of the first aspect of the disclosure, the liquid filtering apparatus

1 may comprise a series of adjacent, operationally aligned filter chamber elements 2. In other words, the filter chamber are placed one after another side by side so as to convey mechanical forces between each other. However, the filter chamber elements 2 do not need to arranged in a straight line, but other formation are may also be envisaged. Moreover, the filter chamber elements 2 are arranged, when in use, immovable in contact with each other. Naturally, they may be detached from each other outside of the normal operation cycle, in connection with service and maintenance, for example.

According to a second aspect of the disclosure, a key 5 is provided for securing a vertically extending filter medium element 4 and for enclosing a top feed opening 3a of a filter chamber 3 in a liquid filtering apparatus 1 according to any of the embodiments and variations of the first aspect, as discussed above.

The key 5 comprises a head portion 5a and a stem portion 5b. The stem portion 5b extends from the head portion towards the filter chamber 3 so as to be at least partly received within the top feed opening 3a of the filter chamber 3. Preferably, but not necessarily, the head portion 5a is arranged to cover the top feed opening so as to enclose the top feed opening 3a.

The key 5 further comprises, within the head portion 5a, an internal fluid channel 5c in fluid communication with at least one hole 5d on the stem portion, so as to provide fluid communication between the internal channel 5c and the filter chamber 3 of the liquid filtering apparatus 1 , when in use.

Preferably, but not necessarily, the key 5 may be configured to secure a filter medium element 4 to a liquid filtering apparatus 1 by pressing said filter medium element 4 between the key 5 and said liquid filtering apparatus, when in use. For example, the key 5 may be dimensioned, with respect to the top feed opening 3a and the filter medium element 4, so that the filter medium element 4 is pressed between the key 5 and the remaining liquid filtering apparatus 1 , when the key 5 is positioned in use. Additionally, or alternatively, the filter medium element 4 may be affixed to the key itself, which in turn, is secured to the remaining liquid filtering apparatus 1 . In such a case the key 5 itself may comprise attachment means, such as one or more threaded holes, protrusion, or the like.

Preferably, but not necessarily, the stem portion 5b of the key 5 may have an at least partially increasing cross-sectional dimension towards the head portion 5a. This provides an at least partly a wedge-shaped form, particularly advantageous for ensuring that the filter medium element 4 is secured, should it be pressed between the key 5 and the top feed opening 3a.

Preferably, but not necessarily, the internal fluid channel 5c may extend in a longitudinal direction of the key 5 along the head portion 5a. Moreover, a plurality of holes 5d may be provided along the stem portion 5b, spaced in a longitudinal direction of the key 5, so as to provide fluid communication between the internal channel 5c and the filter chamber 3 of the liquid filtering apparatus, when in use.

Preferably, but not necessarily, the key 5 may comprises a key feed connection 5e for receiving fluid into the internal channel, and a key discharge connection 5f for discharging fluid from the internal channel 5c. This enables a fluid flow through the internal fluid channel 5c, which is advantageous for flushing the internal fluid channel 5c from any particles blocking the said internal fluid channel 5c, or one or more holes 5d, for example. Such key feed connection 5e and key discharge connection 5f are suitably positioned opposite to each other in a longitudinal direction of the key 5, resulting in such a flushing flow extending over the whole length of the internal fluid channel 5c.

Preferably, but not necessarily, at least one hole 5d on the stem portion 5b of the key 5 has a cross-sectional dimension at least partially decreasing towards the internal fluid channel 5c. This effectively prevents particles blocking one or more holes 5d from being wedged within said hole 5d by the feed pressure pushing such a particle towards a narrowing cross section. Moreover, such construction of the hole 5d even facilitates release of blocking particles, as the feed pressure pushes blocking particles towards a wider cross section.

According to a third aspect of the disclosure, a filter medium element 4 is provided for use in the liquid filtering apparatus 1 according to any of embodiments and variations of the first aspect, as discussed above.

The filter medium element 4 comprises a jacket 4a, a feed opening 4b and discharge opening 4b. The jacket 4a has, when in use, a vertically extending closed circumference defining an inner space, at least laterally limiting the filter chamber 3. The feed opening 4b is arranged to operationally correspond with a top feed opening 3a of the filter chamber 3 for enabling filter material to be fed into the inner space. Suitably, the feed opening 4b is arranged for being attachable to at least a portion of a key 5 so as to secure the filter medium element 4 to the liquid filtering apparatus 1 .

The discharge opening 4c is arranged to operationally correspond with the bottom discharge opening 3b for enabling a filter cake formed within the inner space to be discharged therefrom.

Preferably, but not necessarily, the filter medium element 4 is arranged to be receivable within the filter chamber 3 via the top feed opening 3a thereof. In other words, the dimensioning of the filter medium element 4, with respect to the top feed opening 3a, is arranged such that the filter medium element 4 can be inserted into the filter chamber 3 through the top feed opening 3a.

Preferably, but not necessarily, the filter medium element 4 may further comprises at least one flap 4d extending freely from the level of the feed opening 4b. In such a case, the flap 4d is suitably foldable against a portion of the liquid filtering apparatus outside of and surrounding the top feed opening 3a of the filter chamber 3 so as to facilitate securing the filter medium element 4 to the liquid filtering apparatus LSuitbaly, the filter medium element 4 may then be further secured in place by the flap being pressed between the head portion 5a of the key 5 and said portion of the liquid filtering apparatus outside of and surrounding the top feed opening 3a.

In such a case, the flap 4d may further comprising one or more holes 4d' for receiving, respectively, one or more projections 7 from the portion of the liquid filtering apparatus outside of and surrounding the top feed opening 3a of the respective filter chamber 3, when folded against said portion.

Preferably, but not necessarily, the filter medium element 4 comprises a first layer, such that the jacket 4a of the filter medium element 4 is formed by adjoining at least opposite sides of the first layer, thus defining the vertically extending closed circumference. In such a case, the feed opening 4a, discharge opening 4b, or both, are suitably formed of either or both, respectively, detached section of a side adjacent to the adjoined sides of the first layer.

Alternatively, the filter medium element may comprise a first layer 4' and second layer 4", such that the jacket 4a is formed by adjoining the first layer 4' and the second layer 4" together along respective opposite sides, thus defining the vertically extending closed circumference, when in use. In such a case the feed opening 4a, discharge opening 4b, or both are suitably formed from respective detached sections of the first and second layers. Moreover, at least one flap 4d, as described above, may then be provided as a freely extending section of the first layer, second layer, or both, separated from the second layer, first layer, or each other, respectively.

According to a fourth aspect of the disclosure, a method is provided for operating a liquid filtering apparatus according any of the embodiments and variants of the first aspect, when a key 5 is utilized for securing the filter medium element 4 in place and enclosing the filter chamber top feed opening 3a.

The method comprises a step of feeding filter material into the filter chamber so as to separate filtrate from the filter material with the filter medium element 4 and to form a filter cake within the inner space of the filter medium element 4. Particularly, the filter material is fed through the key 5. After the feeding step, a step of applying compression is carried out, in which compression is applied to the filter chamber 3 externally of the filter medium element 4, so as to extract residual filtrate from the filter cake formed within the filter chamber 3.

During feeding filter material and applying compression, filtrate is received through the filter medium element 4. Preferably, but not necessarily, filtrate is received from at least two sides of the filter chamber 3 during feeding filter material. Depending on the configuration of the liquid filtering apparatus, filtrate may be received from at least two sides of the filter chamber 3 also during compressing.

Finally, a step of discharging the filter cake formed within inner space of the filter medium element 4 is performed.

According to a fifth aspect of the disclosure, a method is provided for servicing a liquid filtering apparatus according any of the embodiments and variants of the first aspect, when a key 5 is utilized for securing the filter medium element 4 in place and enclosing the filter chamber top feed opening 3a.

The method comprises a step of inserting a filter medium element 4 into the intermediate space of the filter chamber element 2 via the top feed opening 3a so as to at least laterally limit the filter chamber 3. The filter medium element 4 is inserted such that the feed opening 4b of the filter medium element 4 is positioned to operationally correspond with the top feed opening 3a of the filter chamber 3. Suitably, also discharge opening 4c is positioned to operationally correspond with the bottom discharge opening 3b.

After the filter medium element has been inserted, the method further comprises a step of inserting a key 5 such that the stem portion 5b is at least partly received within the top feed opening 3a of the filter chamber 3, so as to secure the filter medium element to the liquid filtering apparatus 1 .

Preferably, but not necessarily, the method further comprises the steps of removing the key 5 from the top feed opening 3a of the filter chamber 3, and removing the filter medium element 4 from the intermediate space of the filter chamber element 2 via the top feed opening 3a. It is envisaged, however, that the filter medium element alternatively be withdrawn through the bottom discharge opening 3b.

Fig. 1 illustrates a filter chamber element of a liquid filtering apparatus 1 , said filter chamber element being formed by opposing filter plates 2', 2". It should be noted, that for the purpose of clarity, the liquid filtering apparatus 1 is not illustrated in proportion. Particularly, a height wise section of the liquid filtering is left completely unillustrated, as annotated by the curved dash-dotted lines.

A filter chamber 3 is formed within an intermediate space between the filter plates 2', 2". The filter chamber element 2 may alternatively be provided as a single-piece construction, without the need for separate filter plates. The filter chamber 3 has a top feed opening 3a and bottom discharge opening 3b.

In connection with the filter chamber 3, a drainage arrangement is provided, illustrated in Fig. 1 as a cross-hatched section on both sides of the filter chamber 3 arrangement. A compression arrangement 2b is also provided in in connection with the filter chamber 3, illustrated in Fig. 1 as a sparse dashed line on both sides of the filter chamber 3.

Differentiating from the situation of Fig. 1 , the compression arrangement may be provided on only one side of the filter chamber 3. Moreover, even the drainage arrangement 2a may be provided on only on side of the filter chamber 3, in which case the drainage arrangement 2a and the compression arrangement would be provided on opposite sides.

A filter medium element comprising a first layer 4', 4" is inserted into the filter chamber 3.

Naturally, the filter medium element may be provided with as another type, such as one having a first layer, the opposite ends of which are adjoined to form the closed circumference, as discussed earlier. The filter medium element has a feed opening 4b and a discharge opening 4c.

A key 5 is inserted such that a stem portion 5b thereof is partially inserted within the top feed opening 3a and the feed opening 4b. Moreover, the key 5 is oriented such that the stem portion 5b extends from a head portion 5a towards the filter chamber 3.

Fig. 2 illustrates the liquid filtering apparatus 1 of Fig. 1 equipped with an additional sealing element 6 running along the inner circumference of the top feed opening. Although Fig. 2 presents a situation in which the filter medium element 4 is externally sealed against the top feed opening 3a, other configuration may be utilized for ensuring sufficient sealing. Particularly, the relative location of the sealing element 6 with respect to the key 5, filter chamber 3 and the filter medium element 4, and any additional sealing element, may be varied.

Fig. 3 illustrates the liquid filtering apparatus 1 of Fig. 1 , while schematically representing an internal channel 5c and hole 5d of the key 5 with a dashed line Fig. 4 illustrates the liquid filtering apparatus 1 of Fig. 1 , the filter medium element 4 of which being further equipped with flaps 4d, folded against a portion of the liquid filtering apparatus outside of and surrounding the top feed opening 3a of the filter chamber 3.

Fig. 5 illustrates the liquid filtering apparatus of Fig. 4 further equipped with projections 7 on the portion of the liquid filtering apparatus outside of and surrounding the top feed opening 3a, against which the flap 4d is folded. Respectively, the at least one flap 4d further comprises holes (not illustrated in Fig. 5) for receiving the projections 7.

Although the liquid filter apparatuses of Figs. 1 -5 are presented as having a single filter chamber 3, it should be noted that naturally several filter chambers may be provided on liquid filtering apparatus. To that extent, Fig. 6 illustrates a liquid filtering apparatus 1 equipped with a series of adjacent, operationally aligned filter chamber elements 2 identical to those of Fig. 1 .

Fig. 7 illustrates a key 5 having a head portion 5a, and extending therefrom, a stem portion 5b. Fig. 8 further illustrates the key of Fig. 7, particularly, the internal fluid channel 5c and the hole 5d, represented by the shape formed by the dashed line. Furthermore, Fig. 9 illustrates the key of Figs. 7 and 8 as seen from below the stem portion 5b towards the head portion 5a. From Fig. 9 it can be seen that the internal fluid channel 5c along the longitudinal direction of the key, while a plurality of holes 5d are provided on the stem portion space along the longitudinal direction of the key 5. Moreover, a key feed connection 5e, and a key discharge connection 5f are illustrated positioned opposite to each other in a longitudinal direction of the key 5.

Fig. 10 illustrates filter medium element 4 having a jacket 4a defining a vertically extending closed circumference defining an inner space. A feed opening 4b and a discharge opening 4c are provided on opposing ends of the jacket 4a. Fig. 1 1 illustrates the filter medium element 4 of Fig. 10 further provided with flaps 4d freely extending from the feed opening 4b. In Fig. 12, the filter medium element of Fig. 1 1 is further equipped with holes 4d' on the flaps 4d.