A backwash double-stage pre-filter

Abstract

The application provides a backwashing double-stage pre-filter, comprising two hot melt heads arranged at a water inlet end and a water outlet end respectively for connecting a water pipeline; a valve head in sealing connection with the two hot melt heads, the valve head being internally provided with a water inlet cavity, a water outlet cavity and a filtered water cavity; an upper filter bottle and a lower filter bottle connected to upper and lower ends of the valve head respectively; a first-stage filter assembly arranged in the lower filter bottle for primary filtering of raw water; a second-stage filter assembly arranged in the upper filter bottle for secondary fine filtering of the water filtered in the primary filtering; a valve assembly arranged in the valve head for controlling a water flow direction; a water distributor for guiding the water flow into the first-stage filter assembly; a piston assembly fixedly connected to a bottom of the first-stage filter assembly for driving the first-stage filter assembly to move downward during backwashing; and a valve for switching a filtered water path and a backwashing water path. The application can improve filtering efficiency, enhance filtering effect and prolong service life of the pre-filter.

Description

Technical Field

[0001] This application relates to the field of water purification equipment technology, and more specifically, to a backwashing two-stage pre-filter. Background Technology

[0002] With the improvement of people's living standards and the continuous enhancement of health awareness, the quality of household water is receiving increasing attention. In order to ensure the service life of downstream water-using equipment (such as water heaters, smart toilets, water purifiers, etc.) and the cleanliness of household water, a pre-filter is usually installed under the incoming water pipe or kitchen sink.

[0003] Among pre-filters, dual-screen pre-filters are the most commonly used. However, due to the limited gap design between the screens in existing dual-screen pre-filters, impurities accumulate between the screens over time and are difficult to drain completely, easily leading to clogging. This results in reduced flow rate and decreased water output, affecting household water use and ultimately reducing the overall lifespan of the unit. Utility Model Content

[0004] This application provides a backwashing two-stage pre-filter that can improve filtration efficiency, enhance filtration effect, and extend the service life of the entire pre-filter unit.

[0005] This application provides a backwashing two-stage pre-filter, comprising:

[0006] Two hot-melt heads are respectively located at the water inlet and water outlet for connecting water pipes;

[0007] A valve head, which is sealed to two hot-melt heads, has an inlet chamber, an outlet chamber, and a filter chamber that connects the inlet chamber and the outlet chamber inside the valve head.

[0008] The upper filter bottle and the lower filter bottle are respectively connected to the upper and lower ends of the valve head;

[0009] The first-stage filtration assembly is installed inside the lower filter bottle and is used for primary filtration of the raw water;

[0010] The second-stage filtration component is installed inside the upper filter bottle and is used to perform secondary fine filtration on the water after primary filtration.

[0011] A valve assembly, disposed inside the valve head, is used to control the direction of water flow;

[0012] A water distributor is located at the inlet of the lower filter bottle and is used to guide water flow into the first-stage filtration assembly.

[0013] A piston assembly, fixed to the bottom of the first-stage filter assembly, is used to drive the first-stage filter assembly to move downward during backwashing.

[0014] A valve, located at the lower part of the piston assembly, is used to switch between the filtration water path and the backwash water path.

[0015] In some embodiments, the valve assembly includes a valve body, a valve stem, a valve core, and a one-way valve spring. The valve body has a porous flow channel inside to guide water flow. The valve core is fitted onto the valve stem, and the valve stem is connected to the valve body. The valve core has a valve core hole and a first annular groove. The one-way valve spring is disposed between the valve core and the valve body to press the valve core against the valve stem.

[0016] In some embodiments, the first-stage filter assembly includes a laminated frame and multiple laminated layers. The laminated frame is provided with backwash channels and multiple oblique holes, and the multiple laminated layers are stacked axially on the laminated frame.

[0017] In some embodiments, the second-stage filtration assembly includes a filter screen frame, a filter screen, a pressure cap, and a connecting pipe. The outer wall of the filter screen frame is provided with a third annular groove, and a sealing ring is provided in the third annular groove. The filter screen is sleeved on the outer wall surface of the filter screen frame, and the pressure cap is provided at the upper end of the filter screen to fix the filter screen. The connecting pipe is sleeved inside the filter screen frame and is provided with a connected inlet and outlet. The outlet is connected to the outer cavity of the upper filter bottle.

[0018] In some embodiments, the piston assembly includes a piston and a return spring. The piston is engaged with the laminated frame, the piston has a drain hole, and the return spring is disposed at the bottom of the piston for resetting the piston after backwashing.

[0019] In some embodiments, the inner circumference of the valve core is provided with a ring of inclined grooves, and the bottom of the valve stem is provided with a ring of inclined surfaces. The inclined grooves of the valve core are adapted to the inclined surfaces of the valve stem to close the water passage when the water flow is reversed.

[0020] In some embodiments, the stacked frame is provided with an annular pressing edge, which is used to shut off the filter water path and switch to the backwash water path during backwashing.

[0021] In some embodiments, the inner wall surface of the valve head is provided with a lead-resistant plastic layer.

[0022] In some embodiments, the valve head is provided with an interface, which is connected to a pressure gauge.

[0023] In some embodiments, scale-inhibiting filter media disposed within the laminated frame is also included.

[0024] In this embodiment, a dual-bottle, dual-stage filtration scheme is adopted to achieve highly efficient graded filtration, which can significantly improve filtration efficiency and effect. The backwashing function can effectively clean the filter components, thereby increasing the flow rate and the water output of the downstream water path of the pre-filter, thus affecting household water consumption and extending the overall service life of the pre-filter. This application has a compact structure and reasonable layout, effectively saving operating costs. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0026] Figure 1 A cross-sectional view of a backwashing two-stage pre-filter provided in some embodiments of this application;

[0027] Figure 2 A schematic diagram of a backwashing two-stage pre-filter in a filtering state provided in some embodiments of this application;

[0028] Figure 3 A schematic diagram of a backwashed two-stage pre-filter in a backwashed state, provided for some other embodiments of this application;

[0029] Figure 4 A schematic diagram of the valve head in a backwashing two-stage pre-filter provided in some embodiments of this application;

[0030] Figure 5 A schematic diagram of the filter screen frame in a backwashing two-stage pre-filter provided in some embodiments of this application;

[0031] Figure 6 A schematic diagram of the connecting pipe in a backwashing two-stage pre-filter provided in some embodiments of this application;

[0032] Figure 7 Partial view of the valve body in a backwashing two-stage pre-filter provided in some embodiments of this application;

[0033] Figure 8 A schematic diagram of the valve stem in a backwashing two-stage pre-filter provided in some embodiments of this application;

[0034] Figure 9 A schematic diagram of the valve core in a backwashing two-stage pre-filter provided in some embodiments of this application;

[0035] Figure 10 A schematic diagram of the valve core in a backwashing two-stage pre-filter provided in some embodiments of this application;

[0036] Figure 11 A cross-sectional view of the water distributor in a backwashing two-stage pre-filter provided in some embodiments of this application;

[0037] Figure 12 A schematic diagram of a piston in a backwashing two-stage pre-filter provided in some embodiments of this application;

[0038] Figure 13 A cross-sectional view of a piston in a backwashing two-stage pre-filter provided in some embodiments of this application;

[0039] Figure 14 A schematic diagram of the disc frame in a backwashing two-stage pre-filter provided in some embodiments of this application;

[0040] Figure 15 This is a schematic diagram from another perspective of the disc skeleton in a backwashing two-stage pre-filter provided in some embodiments of this application.

[0041] The attached figures are labeled as follows:

[0042] 1-Heat-fused head; 2-Nut; 3-Valve head; 4-Upper filter bottle; 5-Filter screen; 6-Filter screen frame; 7-Cap; 8-Connecting pipe; 9-Valve body; 10-Valve stem; 11-Valve core; 12-Diverter; 13-Lower filter bottle; 14-Piston; 15-Return spring; 16-Valve; 17-Seal; 18-Plate; 19-Plate frame; 20-One-way valve spring;

[0043] 301 - Valve head internal thread; 302 - Inlet chamber; 303 - Outlet chamber; 304 - First thread; 305 - Backwash chamber; 306 - Filter chamber; 307 - Lead-free plastic layer;

[0044] 601 - Third annular groove; 602 - Outer wall; 801 - Fourth annular groove; 802 - Connector inlet; 803 - Connector outlet; 901 - Second annular groove; 902 - Second thread; 903 - Fourth thread; 904 - Porous flow channel; 1001 - Valve stem external thread; 1002 - Bevel; 1003 - Crimping end face; 1101 - First annular groove; 1102 - Bevel groove; 1103 - Snap-fit; 1104 - Valve core hole ; 1201- Inclined blade hole; 1202- Outer end rib; 1203- Lower end face of water distributor; 1401- Fifth annular groove; 1402- Bottom end groove hole; 1403- Drain hole; 1404- Sixth annular groove; 1405- Abutting end face; 1901- Backwash channel; 1902- Inclined hole; 1903- Laminated frame snap fastener; 1904- Seventh annular groove; 1905- Laminated frame external thread; 1906- Annular pressing edge. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0046] Please refer to Figure 1 Cross-sectional views of a backwashing two-stage pre-filter provided in some embodiments of this application.

[0047] This application provides a backwashing two-stage pre-filter, which mainly includes two hot-melt heads 1, a valve head 3, an upper filter bottle 4 and a lower filter bottle 13, a first-stage filter assembly, a second-stage filter assembly, a valve assembly, a water distributor 12, a piston assembly and a valve 16.

[0048] like Figure 4 As shown. Two heat-fused heads 1 are respectively installed at the inlet and outlet ends of the water pipe for easy connection. A valve head 3 is sealed to the two heat-fused heads 1. The valve head 3 has an inlet chamber 302, an outlet chamber 303, and a filter chamber 306 inside. The filter chamber is located in the middle of the inlet chamber 302 and the outlet chamber 303, and is laterally connected to both chambers. An upper filter bottle 4 and a lower filter bottle 13 are respectively connected to the upper and lower ends of the valve head 3. A second-stage filter assembly and a first-stage filter assembly are installed in the inner cavities of the upper filter bottle 4 and the lower filter bottle 13, respectively. The first-stage filter assembly is used for primary filtration of the raw water, and the second-stage filter assembly is used for secondary fine filtration of the water after primary filtration. A valve assembly is located inside the valve head 3 to control the water flow direction. A water distributor 12 is located at the inlet of the lower filter bottle 13 to guide the water flow into the first-stage filter assembly. The piston assembly is located at the bottom of the first-stage filter assembly and is fixedly connected to it. It drives the first-stage filter assembly downwards during backwashing. Valve 16 is located at the lower part of the piston assembly and is used to switch between the filtration water path and the backwash water path.

[0049] In this embodiment, the hot-melt head 1 connects the water pipe with an inlet at the left end and an outlet at the right end. Before hot-melting, a nut 2 needs to be fitted into it. The hot-melt head 1 has a double-seal design, with a sealing gasket on the end face that contacts the copper head. The nut 2 is fitted onto the hot-melt head and threadedly connected to the valve head 3, which can fix the valve head 3 and press its sealing gasket together to achieve a seal. An annular sealing ring is provided inside the hot-melt head 1, which achieves a side seal. The valve head 3 is made of metal, with threads on both the left and right ends connected to the internal threads of the nut 2. The inlet chamber 302 of the valve head 3 is connected to the lower filter bottle 13, and the outlet chamber 303 is connected to the upper filter bottle 4. The lower part is connected to the lower filter bottle 13 through the first thread 304, and the upper part is connected to the upper filter bottle 4 through the internal thread 301 of the valve head 3.

[0050] In addition, the upper filter bottle 4 can receive filtered water, and its interior is equipped with a second-stage filtration assembly. Its external thread is screwed into the internal thread 301 of the valve head 3. The lower filter bottle 13 receives filtered water, and its interior is equipped with a first-stage filtration assembly. Its external thread is threaded into the internal thread of the valve head 3.

[0051] like Figure 11 As shown. The outer end protrusion 1202 of the water distributor 12 is matched with the groove of the bottle body for limiting. The inclined blade hole 1201 allows raw water to pass through. The lower end face 1203 of the water distributor abuts against the upper end of the first-stage filter assembly. The valve 16, such as a ball valve, is equipped with a switch to control the discharge of sewage. Opening the valve 16 allows for flushing and sewage discharge, while closing the valve 16 activates the filtration mode. Its external thread mates with the sealing element 17.

[0052] like Figure 2 and Figure 3 As shown. The backwashing dual-stage pre-filter provided in this embodiment has the following filtration mode: the source water enters from the left end, passes through the first-stage filter assembly in the lower filter bottle 13, and is then transported from the middle of the filter element to the second-stage filter assembly for second-stage filtration. Finally, it is transported from the outer cavity of the upper filter bottle 4 to the water-using end. The flushing mode is as follows: the bottom valve 16 is opened to discharge sewage, the filter bottle is in a negative pressure state, the piston assembly drives the first-stage filter assembly to move down, the sewage discharge channel inside the valve head 3 is opened, and the water flows from the upper part of the first-stage filter assembly into the backwashing chamber 305 and then flushes the first-stage filter assembly from the inside out. The dirt flows with the water into the backwashing channel 1901 of the first-stage filter assembly for backwashing of the first-stage filter assembly.

[0053] This solution employs a dual-bottle filtration principle. Raw water enters through the left inlet, first undergoing initial filtration through the first-stage filter assembly in the lower filter bottle 13, then flowing through the first-stage filter assembly in the second chamber of the upper filter bottle 4 for a second layer of fine filtration. This dual-bottle chamber-to-chamber filtration structure optimizes the water path, achieving efficient connection. Water finally exits through the right outlet, ensuring sufficient filtration clearance, increasing flow rate, and improving filtration efficiency. During wastewater discharge, water flows from inside the second-stage filter assembly of the upper bottle outwards, then reaches the reverse flushing channel 1901 in the lower filter bottle 13 to flush the discs 18, finally discharging from the lower outlet. This solution optimizes the dual-bottle water path, significantly improving filtration efficiency, achieving efficient connection for water quality that is prone to clogging or difficult to adapt to different environments, and maximizing space utilization, making it suitable for home installation.

[0054] like Figure 7 , Figure 8 , Figure 9 and Figure 10 As shown. In one specific embodiment, the valve assembly includes a valve body 9, a valve stem 10, a valve core 11, and a one-way valve spring 20. The valve body 9 has a porous flow channel inside to guide water flow. The valve core 11 is fitted onto the valve stem 10, and the valve stem 10 is connected to the valve body 9. The valve core 11 has a valve core hole and a first annular groove 1101. The one-way valve spring 20 is disposed between the valve core 11 and the valve body 9, and it is engaged with the upper end of the valve core 11 and the lower end of the valve body 9. It pushes the valve core 11 to press against the pressing end face 1003 of the valve stem 10 to prevent water backflow so that the valve core 11 presses against the valve stem 10.

[0055] Specifically, the second thread 902 of the valve body 9 mates with the external thread 2 of the valve stem, the fourth thread 903 is threadedly connected to the first-stage filter assembly, the valve body 9 is provided with a porous flow channel 904, the first-stage filtered water pushes the valve core 11 into the flow channel 904 and then flows out of the porous flow channel 904, and the first annular groove 1101 is fitted with a sealing ring to seal its gap.

[0056] The threaded rod of valve stem 10 passes through valve core hole 1104 and connects with second thread 902. The inclined groove 1102 of valve core 11 cooperates with the inclined surface 1002 of valve stem 1010 to close the reverse water flow. The snap 1103 of valve core 11 engages with the lower end of one-way valve spring 20. The upper end of one-way valve spring 20 abuts against valve body 9. The force of one-way valve spring 20 pushes valve core 11 downward, thereby closing the downward reverse water path. The second annular groove 901 is fitted with a sealing ring to seal the gap between the first-stage filter assembly (laminated frame 19). Filtered water flow can push valve core 11 upward. Water flow can flow through the inner side of the laminated frame 19 on the outside of valve core 11 and through valve core hole 1104 in the middle of valve core 11.

[0057] like Figure 14 and Figure 15As shown. In one specific embodiment, the first-stage filter assembly includes a stacked disc skeleton 19 and multiple stacked discs 18. The external thread 1905 of the stacked disc skeleton mates with the fourth thread 903 of the valve body 9. The stacked disc skeleton 19 is provided with a backwash channel 1901 and multiple oblique holes 1902. The multiple stacked discs 18 are stacked axially on the stacked disc skeleton 19. The stacked discs 18 are multiple pieces, overlapping and connected together axially. The cross-sections of the water passages can be the same or different, preferably different, to form a complex water passage, so that the pre-filter can meet the filtration requirements of pure stacked discs 18. During backwashing, the stacked discs 18 can be axially released, loosened, and rotated, making the rinsing more thorough. During filtration, they can return to their original state. In addition, a seventh annular groove 1904 is provided on the upper part of the stacked disc skeleton 19. A sealing ring is installed in the seventh annular groove 1904 to seal the gap between the stacked disc skeleton 19 and the water distributor 12.

[0058] When valve 16 is opened to discharge sewage, negative pressure is created inside the lower filter bottle 13. The piston assembly drives the stacked disc skeleton 19 to move downward. At this time, the stacked discs 18 become loose. The stacked disc skeleton 19 closes the filtration water path and switches the backwash water path. The water flows from the backwash chamber 307 of valve head 3 into the interior of upper filter bottle 4 for backwashing, and then flows into the backwash flow channel 1901 of stacked disc skeleton 19 in lower filter bottle 13, where it is obliquely flushed through the inclined hole 1902 to flush the loose stacked discs 18.

[0059] Furthermore, the laminated frame 19 is provided with an annular pressure edge 1906, which closes the filter water path and switches to the backwash water path during backwashing. When the piston assembly drives the laminated frame 19 to move downward, the annular pressure edge 1906 closes the filter water path and switches to the backwash water path, and the water flow enters the upper filter bottle 4 from the backwash chamber 305 of the valve head 3 for backwashing.

[0060] like Figure 5 , Figure 6 As shown. In one specific embodiment, the second-stage filtration assembly includes a filter screen frame 6, a filter screen 5, a pressure cap 7, and a connecting pipe 8. The outer wall of the filter screen frame 6 is provided with a second annular groove 901, and a sealing ring is provided in the second annular groove 901. The filter screen 5 is sleeved on the outer wall surface of the filter screen frame 6, and the pressure cap 7 is provided at the upper end of the filter screen 5 to fix the filter screen 5. The connecting pipe 8 is fitted inside the filter screen frame 6, and the connecting pipe 8 is provided with a connected inlet 802 and an outlet 803. The outlet 803 is connected to the outer cavity of the upper filter bottle 4.

[0061] Specifically, the outer wall 602 of the filter screen frame 6 is fitted onto the filter screen 5, providing support for the filter screen 5 and enabling it to function properly. A sealing ring is installed in the third annular groove 601 to seal the external gap of the filter screen frame 6. The filter screen 5 is fitted onto the outside of the frame, serving as the second-stage filtration component for fine filtration of water. The pressure cap 7 covers the upper end of the filter screen 5, with its top end touching the inner wall of the upper filter bottle 4 to fix the filter screen 5 and prevent it from falling out. The connecting pipe 8 is located inside the filter screen frame 6. The first-stage filtered water flows from the filtration chamber 306 of the valve head 3 into the inlet 802 of the connecting pipe and then from the outlet 803 into the outer cavity of the upper filter bottle 4 for second-stage filtration. The upper and lower parts of the connecting pipe 8 are respectively provided with a fourth annular groove 801, and a sealing ring is installed in the fourth annular groove 801 to seal the gap between the connecting pipe 8 and the filter screen frame 6.

[0062] like Figure 12 and Figure 13 As shown. In one specific embodiment, the piston assembly includes a piston 14 and a return spring 15. The piston 14 is engaged with the stacked plate skeleton 19. The piston 14 has a drain hole, and the return spring 15 is located at the bottom of the piston 14 to reset the piston 14 after backwashing. Specifically, the bottom end slot 1402 of the piston 14 is engaged with the stacked plate skeleton snap 1903, and the abutment end face 1405 abuts against the lower end of the stacked plates 18. During backwashing, the pressure of the water flowing out of the drain hole 1403 will drive the piston 14 to move downward. The return spring 15 is installed in the sixth annular groove 1404, so that the return spring 15 is installed at the bottom of the piston 14. When the backwashing is turned off, the return spring 15 resets the piston 14, and a silicone ring is installed in the fifth annular groove 1401 to slide and seal the gap between the piston and the lower filter bottle 13.

[0063] The valve 16 is sealed and installed at the bottom of the lower filter bottle 13. The bottom end of the lower filter bottle 13 is provided with a sealing element 17. Two sealing rings are installed in the annular groove on the outside of the sealing element 17 to seal the gap between it and the lower filter bottle 13. The water passage hole in the middle of the sealing element 17 is used to discharge sewage. The internal thread of the sealing element 17 is engaged with the external thread of the valve 16.

[0064] To prevent the leaching of heavy metals, a lead-resistant plastic layer 307 can be installed on the inner wall of the valve head 3. The lead-resistant plastic layer 307 is formed by injection molding to prevent heavy metals in the metal valve head 3 from leaching into the water, thus ensuring the safety of drinking water.

[0065] In addition, an interface can be set on the upper part of the valve head 3, and a pressure gauge can be connected to the interface. The pressure gauge can detect the water pressure in the internal flow channel of the valve head 3 in real time, thereby improving the safety of use.

[0066] In addition, scale-inhibiting filter media can be further installed inside the stacked frame 19. The scale-inhibiting filter media can prevent scale formation and improve the filtration effect.

[0067] The backwashing two-stage pre-filter provided in this application has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of this application.

Claims

1. A backwashing two-stage pre-filter, characterized in that, include: Two hot-melt heads (1) are respectively set at the water inlet and water outlet for connecting water pipes; The valve head (3) is sealed to the two hot melt heads (1). The valve head (3) is provided with an inlet chamber (302), an outlet chamber (303) and a filter chamber (306) that connects the inlet chamber (302) and the outlet chamber (303). The upper filter bottle (4) and the lower filter bottle (13) are respectively connected to the upper and lower ends of the valve head (3); The first-stage filtration assembly is installed inside the lower filter bottle (13) and is used for primary filtration of the raw water. The second-stage filtration assembly is installed inside the upper filter bottle (4) and is used to perform secondary fine filtration on the water after primary filtration. A valve assembly, located inside the valve head (3), is used to control the direction of water flow; A water distributor (12) is installed at the inlet of the lower filter bottle (13) to guide water flow into the first-stage filtration assembly; A piston assembly, fixed to the bottom of the first-stage filter assembly, is used to drive the first-stage filter assembly to move downward during backwashing. A valve (16) is located at the lower part of the piston assembly and is used to switch between the filter water path and the backwash water path.

2. The backwashing dual-stage pre-filter according to claim 1, characterized in that, The valve assembly includes a valve body (9), a valve stem (10), a valve core (11), and a one-way valve spring (20). The valve body (9) has a porous flow channel (904) inside to guide water flow. The valve core (11) is fitted onto the valve stem (10). The valve stem (10) is connected to the valve body (9). The valve core (11) has a valve core hole (1104) and a first annular groove (1101). The one-way valve spring (20) is disposed between the valve core (11) and the valve body (9) so that the valve core (11) presses against the valve stem (10).

3. The backwashing dual-stage pre-filter according to claim 1, characterized in that, The first-stage filter assembly includes a stacked plate frame (19) and multiple stacked plates (18). The stacked plate frame (19) is provided with a backwash channel (1901) and multiple oblique holes (1902). The multiple stacked plates (18) are stacked axially on the stacked plate frame (19).

4. The backwashing two-stage pre-filter according to claim 1, characterized in that, The second-stage filtration assembly includes a filter screen frame (6), a filter screen (5), a pressure cap (7), and a connecting pipe (8). The outer wall of the filter screen frame (6) is provided with a third annular groove (601), and the third annular groove (601) is provided with a sealing ring. The filter screen (5) is fitted onto the outer wall of the filter screen frame (6), and the pressure cap (7) is located at the upper end of the filter screen (5) to fix the filter screen (5). The connecting pipe (8) is fitted into the interior of the filter screen frame (6), and the connecting pipe (8) is provided with a connected inlet (802) and an outlet (803). The outlet (803) is connected to the outer cavity of the upper filter bottle (4).

5. The backwashing dual-stage pre-filter according to claim 3, characterized in that, The piston assembly includes a piston (14) and a return spring (15). The piston (14) is engaged with the stacked frame (19). The piston (14) has a drain hole (1403). The return spring (15) is located at the bottom of the piston (14) and is used to reset the piston (14) after backwashing.

6. The backwashing dual-stage pre-filter according to claim 2, characterized in that, The valve core (11) has a ring of inclined grooves (1102) distributed around its inner circumference, and the bottom of the valve stem (10) has a ring of inclined surface (1002). The inclined grooves (1102) of the valve core (11) are adapted to the inclined surface (1002) of the valve stem (10) to close the water passage when the water flow is reversed.

7. The backwashing dual-stage pre-filter according to claim 3, characterized in that, The stacked frame (19) is provided with an annular pressing edge (1906), which is used to close the filter water path and switch to the backwash water path during backwashing.

8. The backwashing two-stage pre-filter according to any one of claims 1 to 7, characterized in that, The inner wall of the valve head (3) is provided with a lead-resistant plastic layer (307).

9. The backwashing two-stage pre-filter according to any one of claims 1 to 7, characterized in that, The valve head (3) is provided with an interface, which is connected to a pressure gauge.

10. The backwashing two-stage pre-filter according to claim 3, characterized in that, It also includes scale-inhibiting filter media disposed inside the stacked frame (19).

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