CN110856779A

CN110856779A - Composite filter element and filtering system

Info

Publication number: CN110856779A
Application number: CN201810964974.XA
Authority: CN
Inventors: 李文明; 陈琦; 黄燕
Original assignee: AO Smith China Environmental Products Co Ltd; AO Smith Corp
Current assignee: AO Smith China Water Heater Co Ltd; AO Smith China Environmental Products Co Ltd; AO Smith Corp
Priority date: 2018-08-23
Filing date: 2018-08-23
Publication date: 2020-03-03

Abstract

The embodiment of the application discloses composite filter element and filtration system, wherein composite filter element includes leading filter unit, membrane filtration unit, the rearmounted filter unit that communicates in proper order along water flow direction, membrane filtration unit is located leading filter unit with rearmounted filter unit's the outside, membrane filtration unit centers on leading filter unit with rearmounted filter unit sets up. Under a certain volume of the composite filter element, the membrane surface area of the membrane filtration unit can be increased as much as possible. Since the life of the composite filter element is basically equal to that of the membrane filtration unit, the life of the composite filter element can be prolonged under the condition of increasing the membrane surface area of the membrane filtration unit.

Description

Composite filter element and filtering system

Technical Field

The application relates to the field of water treatment, in particular to a composite filter element and a filter system.

Background

In the prior art, in order to minimize the volume of the filtration system, a plurality of filtration units are often combined in one filter element. For example, chinese patent application entitled "composite filter element and composite filter element assembly having the same" in chinese patent library and publication No. CN205346995U "and chinese patent application entitled" filter element and water purifier "in chinese patent library and publication No. CN 205287841U" both disclose composite filter elements.

However, the composite filter element has more or less defects. For example, the structure and flow channel arrangement of the composite filter element are complex. For another example, the composite filter element has a short life. For another example, the composite filter element has a large volume (particularly, the width of the composite filter element) and is not suitable for installation.

Disclosure of Invention

In order to overcome the above-mentioned drawbacks of the prior art, the present application provides a composite filter element and a filter system, which can solve at least one of the above-mentioned problems.

The embodiment of the application discloses composite filter element, include along leading filter unit, membrane filtration unit, the rearmounted filter unit of rivers direction intercommunication in proper order, membrane filtration unit is located leading filter unit with rearmounted filter unit's the outside, membrane filtration unit centers on leading filter unit with rearmounted filter unit sets up.

Preferably, the pre-filtration unit, the post-filtration unit and the membrane filtration unit are arranged in parallel.

Preferably, the membrane filter unit comprises a central tube, the membrane filter unit is rolled on the central tube, the central tube is provided with a first chamber and a second chamber which are parallel to the axis direction and arranged in parallel, the front filter unit is positioned in the first chamber, and the rear filter unit is positioned in the second chamber.

Preferably, the central tube is oval or elongated.

Preferably, the central tube is formed with a through hole for communicating the second chamber with the membrane filtration unit.

Preferably, the wastewater outlet and the pure water outlet of the membrane filtration unit are located at the short sides of the membrane filtration unit.

Preferably, the filter comprises an end cap arranged at both ends of the central tube, and the end cap is formed with a fourth channel communicated with the inlet of the front filter unit.

Preferably, a membrane shell is included, and the end cover or the membrane shell and the end cover jointly form a first channel for communicating the outlet of the pre-filtration unit with the inlet of the membrane filtration unit, a second channel for communicating with the waste water outlet of the membrane filtration unit, and a third channel for communicating with the outlet of the post-filtration unit.

Preferably, at least two or more of the inlet of the pre-filter unit, the outlet of the pre-filter unit, the inlet of the membrane filter unit and the outlet of the post-filter unit are positioned at the same end of the composite filter element.

Preferably, the front filter unit and/or the rear filter unit can be separated from the central tube from the other end of the composite filter element.

The embodiment of the application discloses filtration system, include composite filter element and water pump as above, the water pump with leading filter unit's entry intercommunication, or, the water pump sets up leading filter unit's export with between membrane filter unit's the entry.

Preferably, the water inlet device comprises a water inlet flow channel communicated with an inlet of the pre-filtering unit, and a water inlet electromagnetic valve is arranged on the water inlet flow channel.

Preferably, the outlet of the post-filter unit is in communication with a faucet.

Preferably, a combination valve or waste water ratio is included in communication with the waste water outlet of the membrane filtration unit.

The embodiment of the application discloses composite filter element, include first filter unit, second filter unit, the third filter unit that communicates in proper order along the rivers direction, first filter unit with the third filter unit extends along an axis direction, first filter unit with the third filter unit sets up side by side.

Preferably, the filter comprises a central tube, a first chamber and a second chamber which are arranged in parallel are arranged inside the central tube, the first filter unit is positioned in the first chamber, and the third filter unit is positioned in the second chamber.

Preferably, the first filter unit is detachably disposed in the first chamber, and/or the third filter unit is detachably disposed in the second chamber.

Preferably, the first filter unit and the third filter unit are detachable from the same end of the composite filter element from the central tube.

Preferably, the second filter element is rolled outside the central tube.

Preferably, the first filter unit and the third filter unit are arranged at intervals, or the first filter unit is sleeved on the outer side or the inner side of the third filter unit.

The embodiment of the application discloses filtration system, include composite filter element and water pump as above, the water pump with first filter unit's entry intercommunication, or, the water pump sets up first filter unit's export with between the entry of second filter unit.

Preferably, the filter comprises a water inlet flow channel communicated with an inlet of the first filtering unit, and a water inlet electromagnetic valve is arranged on the water inlet flow channel.

The embodiment of the application discloses composite filter element, be in including center tube, formation leading filtration runner and the rearmounted filtration runner of center tube inboard and being located the membrane filtration runner in the center tube outside, leading filtration runner the membrane filtration runner and rearmounted filtration runner communicates according to the preface.

Preferably, the wall surface of the central tube is provided with a through hole for communicating the membrane filtration flow channel with the pre-filtration flow channel.

Preferably, the inlet of the pre-filtering flow passage, the outlet of the pre-filtering flow passage, the inlet of the membrane filtering flow passage and the outlet of the post-filtering flow passage are located at the same end of the composite filter element.

Preferably, the composite filter element comprises a membrane filtration unit for forming the membrane filtration flow channel, the membrane filtration unit is provided with a raw water inlet and a pure water outlet, the raw water inlet of the membrane filtration unit is communicated with the outlet of the front filtration flow channel, and the pure water outlet of the membrane filtration unit is communicated with the inlet of the rear filtration flow channel.

The embodiment of the application adopts the structure to have the advantages that:

1. under a certain volume of the composite filter element, the membrane surface area of the membrane filtration unit can be increased as much as possible. Since the life of the composite filter element is basically equal to that of the membrane filtration unit, the life of the composite filter element can be prolonged under the condition of increasing the membrane surface area of the membrane filtration unit.

2. The inlets or outlets of the plurality of flow passages are located at the same end, thereby facilitating installation and simplifying the flow passages;

3. the side wall of the central tube is provided with a through hole for communicating the membrane filtration unit and the post-filtration unit (or the second filtration unit and the third filtration unit), so that the structure can be simplified.

4. The central tube is oval or elongated to fit in the installation space.

Drawings

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. In addition, the shapes, the proportional sizes, and the like of the respective members in the drawings are merely schematic for assisting the understanding of the present application, and are not particularly limited to the shapes, the proportional sizes, and the like of the respective members in the present application. Those skilled in the art, having the benefit of the teachings of this application, may select various possible shapes and proportional sizes to implement the present application, depending on the particular situation.

Fig. 1 shows a schematic cross-sectional structure of a composite filter element in an embodiment of the present application.

Fig. 2 shows a schematic cross-sectional view of the composite filter element of fig. 1 with the membrane shell and the membrane cover removed.

Fig. 3 shows a schematic cross-sectional view of a composite filter element according to another embodiment of the present disclosure.

Fig. 4 shows a schematic cross-sectional view of a composite filter element according to yet another embodiment of the present application.

Fig. 5 shows a schematic water circuit diagram of a filtration system employing the composite filter element of fig. 1.

Fig. 6 shows a water path structure diagram of a filtration system using the composite cartridge of fig. 1.

Reference numerals of the above figures: 11. a pre-filter unit; 12. a membrane filtration unit; 13. a post-filtration unit; 2. a central tube; 21. a first chamber; 22. a second chamber; 23. a through hole; 31. an end cap; 311. a through hole; 32. a membrane shell; 33. a membrane cover; 41. a first channel; 42. a second channel; 43. a third channel; 44. a fourth channel; 5. an opening and closing mechanism; 61. a first filter unit; 62. a second filter unit; 63. a third filtering unit; 71. a pre-filter flow channel; 72. a membrane filtration flow channel; 73. a post-filtration flow channel; 81. a water inlet flow channel; 82. a water inlet electromagnetic valve; 83. a primary filter screen; 84. an integral three-way valve; 85. a faucet; 86. a combination valve; 87. a water pump; 88. a composite filter element.

Detailed Description

The details of the present application can be more clearly understood in conjunction with the accompanying drawings and the description of the specific embodiments of the present application. However, the specific embodiments of the present application described herein are for the purpose of illustration only and are not to be construed as limiting the application in any way. The skilled person, in the light of the teachings of this application, may conceive of any possible variant based on this application, which shall be considered to fall within the scope of this application.

The embodiment of the application discloses composite filter element 88, include along leading filter unit 11, membrane filter unit 12, the rearmounted filter unit 13 of rivers direction intercommunication in proper order, membrane filter unit 12 is located leading filter unit 11 with the outside of rearmounted filter unit 13, membrane filter unit 12 centers on leading filter unit 11 with rearmounted filter unit 13 sets up.

With the above structure, the membrane surface area of the membrane filtration unit 12 can be increased as much as possible within a certain volume of the composite filter element 88. Since the life of the composite filter element 88 is mainly determined by the life of the membrane filtration unit 12, the life of the composite filter element 88 can be extended while increasing the membrane surface area of the membrane filtration unit 12.

Referring to fig. 1 and 2, the embodiment of the application discloses a composite filter element 88, and the composite filter element 88 comprises a central tube 2 parallel to the axial direction. The inner side of the center tube 2 has a first chamber 21 and a second chamber 22 arranged side by side in parallel to the axial direction of the center tube 2. Specifically, the center tube 2 has a surrounding wall and a spacer provided inside the surrounding wall. Which divides the inside of the wall into a first chamber 21 and a second chamber 22. The pre-filter unit 11 and the post-filter unit 13 are located in the first chamber 21 and the second chamber 22, respectively. Generally, the first and

second chambers

21 and 22 have a cylindrical shape in order to be adapted to the shapes of the pre-filter unit 11 and the post-filter unit 13.

In the present embodiment, the pre-filter unit 11 may include a carbon fiber filter element. The post-filter unit 13 may comprise granular activated carbon. Of course, in other alternative embodiments, the pre-filter unit 11 and the post-filter unit 13 may also be other filter elements as needed, and are not limited herein.

The membrane filtration unit 12 is rolled on the outside of the central tube 2. In this embodiment, the membrane filtration unit 12 comprises a reverse osmosis membrane cartridge. Of course, in other alternative embodiments, the membrane filtration unit 12 may be a nanofiltration membrane cartridge, an ultrafiltration membrane cartridge, or the like.

The reverse osmosis membrane filter element is provided with a raw water inlet, a waste water outlet and a pure water outlet. Considering that the runner design is simple, the raw water entry of reverse osmosis membrane filter core is located composite filter 88's at least one of them one end tip, reverse osmosis membrane's waste water export is located the short side in the outside, reverse osmosis membrane's pure water export is located the short side of inboard. The central tube 2 is formed with a through hole 23 for communicating the second chamber 22 with the membrane filtration unit 12. Pure water led out from the pure water outlet of the reverse osmosis membrane filter element can enter the second chamber 22 through the through hole 23 and then be filtered through the post-filter element unit. Optionally, the raw water inlet may also be located at both ends of the composite filter element 88.

Referring to fig. 1, in the present embodiment, the composite filter element 88 may further include a membrane housing 32 disposed outside the central tube 2, a membrane cover 33 disposed at an end of the membrane housing 32, and two end caps 31 disposed at both ends of the central tube 2, respectively. The reverse osmosis membrane cartridge is arranged between the membrane housing 32 and the central tube 2. The space between the outer sidewall of the reverse osmosis membrane cartridge and the membrane housing 32 can be used to receive the wastewater flowing out of the wastewater outlet of the reverse osmosis membrane cartridge.

Referring to fig. 2, in order to communicate the pre-filter unit 11, the membrane filter unit 12 and the post-filter unit 13 in sequence, the end cap 31 or the membrane housing 32 and the end cap 31 together form a first passage 41 for communicating the outlet of the pre-filter unit 11 with the inlet of the membrane filter unit 12, a second passage 42 for communicating with the waste water outlet of the membrane filter unit 12, a third passage 43 for communicating with the outlet of the post-filter unit 13, and a fourth passage 44 (inlet flow passage) for communicating with the inlet of the pre-filter unit 11.

In view of installation convenience, in the present embodiment, the open end of the fourth channel 44 (i.e., the inlet of the pre-filter unit 11), the open end of the third channel 43 (i.e., the outlet of the post-filter unit 13), the outlet of the pre-filter unit 11, the raw water inlet of the membrane filter unit 12, and the open end of the second channel 42 (i.e., the wastewater outlet of the membrane filter unit 12) may all be located at the same end (upper end in the drawing) of the composite filter element 88. Of course, in other alternative embodiments, the open end of the fourth channel 44 (i.e., the inlet of the pre-filter unit 11), the open end of the third channel 43 (i.e., the outlet of the post-filter unit 13), the outlet of the pre-filter unit 11, the raw water inlet of the membrane filter unit 12, and the open end of the second channel 42 (i.e., the waste water outlet of the membrane filter unit 12) may also be disposed at different ends or other positions of the composite filter element 88 as required.

Typically, one end (the lower end in fig. 1) of the membrane housing 32 is closed. The upper end of the membrane housing 32 is provided with a membrane cover 33. When the central tube 2, to which the pre-filter unit 11, the post-filter unit 13, and the membrane filter unit 12 are attached, is inserted into the membrane housing 32, the other end (upper end in fig. 1) of the membrane housing 32 may be sealed by the membrane cover 33.

With the above configuration, the raw water enters the pre-filter unit 11 through the fourth passage 44, and flows into the raw water inlet of the membrane filter unit 12 through the inside of the first passage 41 to the outside after being filtered by the pre-filter unit 11. Pure water produced by filtration in the membrane filtration unit 12 enters the post-filter unit 13 from the outside to the inside through the through-holes 23, and is discharged from the third passage 43 to the outside after being filtered in the post-filter unit 13. The waste water generated by the filtration in the membrane filtration unit 12 is discharged to the outside through the second passage 42.

Referring to fig. 2, in other words, in the composite filter element 88 of the embodiment of the present application, the front filter flow path 71 and the rear filter flow path 73 of the composite filter element 88 are both located inside the center tube 2, and the membrane filter flow path 72 is located outside the center tube 2. The inlet of the pre-filtration flow path 71, the outlet of the pre-filtration flow path 71, the inlet of the membrane filtration flow path 72, and the outlet of the post-filtration flow path 73 are located at the same end (upper end in fig. 2) of the composite filter element 88.

In the present embodiment, as shown in fig. 2, the bottom wall of the center pipe 2 is closed and non-openable. The end cap 31 at the lower end of the central tube 2 does not have a through hole 23 for passing the central tube 2 for the sake of structural simplicity. In the present embodiment, the pre-filter unit 11 and the post-filter unit 13 are fixed in the center tube 2 and cannot be taken out of the center tube 2.

In an alternative embodiment, as shown with reference to fig. 3, unlike the previous embodiment, the pre-filter unit 11 and the post-filter unit 13 can be detached from the central tube 2 from the other end (lower end in fig. 3) of the composite filter element 88. The end cap 31 at the lower end of the composite filter element 88 has a through hole 311 through which the center tube 2 passes. The lower end of the center tube 2 passes through the through hole 311 and is positioned below the end cap 31. An opening/closing mechanism 5 corresponding to the first chamber 21 and the second chamber 22 is provided on the bottom wall of the center pipe 2. When the pre-filter unit 11 and the post-filter unit 13 need to be replaced, the corresponding chamber (the first chamber 21 and/or the second chamber 22) can be opened through the opening and closing mechanism 5, so that the pre-filter unit 11 and/or the post-filter unit 13 can be taken out, and then a new pre-filter unit 11 and/or the post-filter unit 13 is put into the first chamber 21 and/or the second chamber 22.

In a preferred embodiment, the central tube 2 is oval or elongated. It is contemplated that the space under the cabinet is generally slim, i.e., less space is left for the width of the composite filter element 88. To adapt to such a space, the length of the central tube 2 can be increased as much as possible, and the width can be correspondingly reduced. Thus, the membrane filtration unit 12 wound around the central tube 2 still has a large membrane filtration area.

Referring to fig. 5 and 6, the embodiment of the present application further discloses a filtering system, which includes a composite filter element 88 as described above and a water pump 87, wherein the water pump 87 is communicated with the inlet of the pre-filtering unit 11.

In the present embodiment, the filtration system includes a water inlet channel 81 communicating with an inlet of the pre-filter unit 11, and a water inlet solenoid valve 82 is provided on the water inlet channel 81. A primary filter screen 83 and an integral three-way valve 84 may also be provided upstream of the water inlet solenoid valve 82 to receive tap water. The outlet of the post-filter unit 13 communicates with a water tap 85 to discharge pure water to the outside. In this embodiment, the composite filter element 88 includes a combination valve 86 in communication with the waste water outlet of the membrane filtration unit 12 for outwardly discharging the waste water. In another alternative embodiment, the waste water outlet of the membrane filtration unit 12 is not provided with a combination valve 86. To accomplish the waste water draining and flushing functions, the composite filter element 88 includes the waste water ratio in communication with the waste water outlet of the membrane filtration unit 12 and a flushing flow passage in parallel with the waste water ratio.

In another alternative embodiment, the water pump 87 is disposed in communication between the outlet of the pre-filter unit 11 and the inlet of the membrane filter unit 12.

Referring to fig. 4, the present embodiment further discloses a composite filter element 88, which includes a first filter unit 61 (e.g., a front filter unit 11), a second filter unit 62 (e.g., a membrane filter unit 12), and a third filter unit 63 (e.g., a rear filter unit 13) that are sequentially connected in a water flow direction, where the first filter unit 61 and the third filter unit 63 extend along an axial direction, and the first filter unit 61 and the third filter unit 63 are arranged in parallel.

The front filter unit 11 and the rear filter unit 13 of the composite filter element 88 in the prior art are arranged at intervals. This results in a complicated waterway structure requiring more sealing elements.

Compared with the composite filter element 88 in the prior art, the first filter unit 61 and the third filter unit 63 of the composite filter element 88 are arranged at intervals. Accordingly, the first filter unit 61 and the third filter unit 63 may be separated by a sidewall of the center tube 2 or a partition inside the center tube 2. Therefore, the composite filter element 88 in the embodiment of the present application has a simpler waterway structure and fewer sealing elements.

In the present embodiment, the composite filter element 88 may include a central tube 2, the central tube 2 is provided with a first chamber 21 and a second chamber 22 which are arranged in parallel, the first filter unit 61 is located in the first chamber 21, and the third filter unit 63 is located in the second chamber 22. The second filter unit 62 is rolled on the outside of the central tube 2.

The first filter unit 61 is detachably provided in the first chamber 21, and/or the third filter unit 63 is detachably provided in the second chamber 22. The composite filter element 88 of the prior art is difficult or almost impossible to replace the first filter unit 61 or the third filter unit 63, but the first filter unit 61 and the third filter unit 63 can be selectively replaced because the composite filter element 88 of the embodiment of the present application has a simple structure.

In particular, the inlet and/or outlet of the first filter unit 61 and the outlet of the third filter unit 63 may be located at one end of the composite filter element 88 in view of installation convenience and simple water path. For easy replacement, the first filter unit 61 and the third filter unit 63 can be detached from the central tube 2 from the other end of the composite filter element 88.

Of course, in another alternative embodiment, the first filter unit 61 may be sleeved outside the central tube 2, and the second filter unit 62 and the third filter unit 63 are located inside the central tube 2. Alternatively, in another alternative embodiment, the third filter unit 63 may be sleeved on the outer side of the central tube 2, and the second filter unit 62 and the first filter unit 61 are located on the inner side of the central tube 2.

The embodiments in the present specification are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.

The above embodiments are merely illustrative of the technical concepts and features of the present application, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present application and implement the present application, and not to limit the protection scope of the present application. All equivalent changes and modifications made according to the spirit of the present application should be covered in the protection scope of the present application.

Claims

1. The utility model provides a composite filter element, its characterized in that includes leading filter unit, membrane filtration unit, the rearmounted filter unit that communicates in proper order along the rivers direction, membrane filtration unit is located leading filter unit with rearmounted filter unit's the outside, membrane filtration unit centers on leading filter unit with rearmounted filter unit sets up.

2. The composite filter element of claim 1, wherein the pre-filter unit, the post-filter unit, and the membrane filter unit are arranged in parallel.

3. The composite filter element of claim 1, comprising a center tube, the membrane filtration unit being rolled onto the center tube, the center tube having a first chamber and a second chamber arranged side by side parallel to the axial direction, the pre-filter unit being located in the first chamber and the post-filter unit being located in the second chamber.

4. The composite filter element of claim 3, wherein the center tube is oval or elongated.

5. The composite filter element of claim 3, wherein the center tube has a through hole formed therein for communicating the second chamber with the membrane filtration unit.

6. The composite filter element of claim 5, wherein the wastewater outlet and the pure water outlet of the membrane filtration unit are located at the short sides of the membrane filtration unit.

7. The composite filter element of claim 3, comprising end caps disposed at both ends of the center tube, the end caps being formed with fourth channels communicating with the inlet of the pre-filter element.

8. The composite filter element according to claim 7, comprising a membrane shell, the end cap or the membrane shell and the end cap together forming a first channel for communicating the outlet of the pre-filter unit with the inlet of the membrane filter unit, a second channel for communicating with the waste water outlet of the membrane filter unit, a third channel for communicating with the outlet of the post-filter unit.

9. The composite filter cartridge of claim 3, wherein at least two or more of the inlet of the pre-filter unit, the outlet of the pre-filter unit, the inlet of the membrane filter unit, and the outlet of the post-filter unit are located at the same end of the composite filter cartridge.

10. The composite filter element according to claim 9, wherein the pre-filter element and/or the post-filter element can be detached from the central tube from the other end of the composite filter element.

11. A filtration system comprising a composite filter element according to any one of claims 1 to 10 and a water pump in communication with the inlet of the pre-filter unit or the water pump is disposed between the outlet of the pre-filter unit and the inlet of the membrane filter unit.

12. The filtration system of claim 11, comprising a water inlet channel in communication with the inlet of the pre-filter unit, wherein the water inlet channel is provided with a water inlet solenoid valve.

13. The filtration system of claim 11, wherein the outlet of the post-filter unit is in communication with a faucet.

14. A filtration system according to claim 11, comprising a combination valve or waste water ratio in communication with the waste water outlet of the membrane filtration unit.

15. The utility model provides a composite filter element, its characterized in that includes first filter unit, second filter unit, the third filter unit that communicates in proper order along rivers direction, first filter unit with the third filter unit extends along an axial direction, first filter unit with the third filter unit sets up side by side.

16. The composite filter element of claim 15, comprising a center tube having a first chamber and a second chamber disposed side by side within the center tube, the first filter unit being located in the first chamber and the third filter unit being located in the second chamber.

17. The composite filter cartridge of claim 16, wherein the first filter unit is removably disposed within the first chamber and/or the third filter unit is removably disposed within the second chamber.

18. The composite filter element of claim 15, wherein the first filter element and the third filter element are detachable from the composite filter element from the same end of the composite filter element.

19. The composite filter element of claim 16, wherein the second filter element is wrapped outside the center tube.

20. The composite filter element according to claim 15, wherein the first filter unit and the third filter unit are arranged at intervals, or the first filter unit is sleeved outside or inside the third filter unit.

21. A filtration system comprising a composite filter element according to any one of claims 15 to 20 and a water pump in communication with the inlet of the first filtration unit or the water pump is disposed between the outlet of the first filtration unit and the inlet of the second filtration unit.

22. The filtration system of claim 21, comprising a water inlet channel in communication with the inlet of the first filtration unit, the water inlet channel having a water inlet solenoid valve disposed thereon.

23. The filtration system of claim 21, wherein the outlet of the third filtration unit is in communication with a faucet.

24. A filtration system according to claim 21, comprising a combination valve or waste water ratio in communication with the waste water outlet of the membrane filtration unit.

25. The composite filter element is characterized by comprising a central tube, a front filtering flow channel and a rear filtering flow channel which are formed on the inner side of the central tube, and a membrane filtering flow channel which is positioned on the outer side of the central tube, wherein the front filtering flow channel, the membrane filtering flow channel and the rear filtering flow channel are communicated in sequence.

26. The composite filter element of claim 25, wherein the wall of the center tube is provided with through holes communicating the membrane filtration flow path with the post-filtration flow path.

27. The composite filter element of claim 25, wherein the inlet of the pre-filter flow path, the outlet of the pre-filter flow path, the inlet of the membrane filter flow path, and the outlet of the post-filter flow path are at the same end of the composite filter element.

28. The composite filter element as claimed in claim 25, which comprises a membrane filtration unit for forming the membrane filtration flow path, the membrane filtration unit having a raw water inlet and a pure water outlet, the raw water inlet of the membrane filtration unit communicating with the outlet of the pre-filtration flow path, the pure water outlet of the membrane filtration unit communicating with the inlet of the post-filtration flow path.