Air filter of hydrogen fuel cell system

Abstract

The utility model discloses an air filter of a hydrogen fuel cell system, which relates to the technical field of air filters and comprises a filter shell and a filter element arranged in the filter shell, and a filter air inlet pipe and a filter air outlet pipe are arranged on the filter shell. The filter element is provided with a filter air outlet cavity communicated with the filter air outlet pipe, the filter air inlet pipe is connected with a prefilter, the filter element is sleeved with a cylindrical prefilter cover, and the prefilter cover and the filter shell jointly define a filter air inlet cavity communicated with the filter air inlet pipe. The prefilter is used for performing primary prefiltration on air; the pre-filtering cover is used for performing secondary pre-filtering on the air subjected to primary pre-filtering, and the filter element is used for performing fine filtering on the air subjected to secondary pre-filtering. The air filter of the hydrogen fuel cell system provided by the utility model is long in service life, and the use and maintenance cost of a user is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of air filters, in particular to an air filter for a hydrogen fuel cell system. Background Art

[0002] At present, most fuel cell systems used in construction machinery vehicles are equipped with air filters, which are used to provide clean air for these construction machinery vehicles. The air filters should not only remove impurities in the air to prevent the fuel cell engines of these construction machinery vehicles from inhaling air with impurities during operation and increasing the chance of abrasion and damage, but also effectively remove harmful chemical gas impurities (SO2, NOx, NH3, VOCs, etc.) in the air to avoid catalyst poisoning in the fuel cell engine, which may lead to degradation of the stack performance and premature termination of its life.

[0003] However, the filter element of the air filter is a wearing part with a short service life. The filter elements of the air filters commonly used in the market need to be cleaned or replaced regularly. If the cleaning or replacement is not timely, it will seriously affect the service life of the fuel cell engine and cause great losses to the user, which greatly increases the user's use and maintenance costs. Utility Model Content

[0004] In view of the above defects in the prior art, the utility model provides an air filter for a hydrogen fuel cell system. The air filter for the hydrogen fuel cell system has a long service life and reduces the use and maintenance costs of users.

[0005] In order to solve the above technical problems, the technical solution adopted by the utility model is:

[0006] A hydrogen fuel cell system air filter comprises a filter housing and a filter element arranged in the filter housing, the filter housing being provided with a filter inlet pipe and a filter outlet pipe, the filter element being provided with a filter outlet cavity connected to the filter outlet pipe, the filter inlet pipe being connected with a pre-filter, the filter element being provided with a cylindrical pre-filter cover, the pre-filter cover and the filter housing together forming a filter inlet cavity connected to the filter inlet pipe; the pre-filter is used for performing a primary pre-filtration on air; the pre-filter cover is used for performing a secondary pre-filtration on air that has been pre-filtered at the primary level, and the filter element is used for fine filtering of air that has been pre-filtered at the secondary level.

[0007] Wherein, the filter element comprises a main filter element and a safety filter element coaxially sleeved inside the main filter element, the pre-filter cover is coaxially sleeved outside the main filter element, and the inner cavity of the safety filter element is the filter outlet cavity.

[0008] Wherein, the pre-filter cover comprises primary filter cotton, medium filter cotton and high efficiency filter cotton which are sequentially stacked from the outside to the inside.

[0009] Wherein, the pre-filter includes a pre-filter housing, a guide assembly fixedly arranged in the pre-filter housing, and an impeller assembly arranged on the guide assembly, the pre-filter housing is provided with a pre-filter air inlet, a pre-filter air outlet and a pre-filter sewage outlet, the pre-filter air outlet is connected to the filter inlet pipe, the guide assembly is used to guide the air entering from the pre-filter air inlet, and the impeller assembly is used to discharge the impurities separated by centrifugation into the pre-filter sewage outlet.

[0010] Wherein, the pre-filter housing includes a pre-filter cylinder with openings at both ends, a rain cap cover arranged at one end of the pre-filter cylinder and an air outlet and sewage cover arranged at the other end of the pre-filter cylinder, a screen structure is arranged on the end of the pre-filter cylinder close to the rain cap cover, all mesh holes of the screen structure together constitute the pre-filter air inlet, and the pre-filter air outlet and the pre-filter sewage outlet are both arranged on the air outlet and sewage cover.

[0011] Among them, one end of the air outlet and sewage cover is provided with a accommodating chamber connected with the inner cavity of the pre-filter cylinder, and the other end of the air outlet and sewage cover is provided with a pre-filter outlet pipe, and the pre-filter outlet port is opened on the bottom wall of the accommodating chamber and connects the accommodating chamber and the pre-filter outlet pipe; a plurality of guide plates are provided on the bottom wall of the accommodating chamber, all of the guide plates are arranged in a circular array with the axis of the air outlet and sewage cover as the central axis, and all of the guide plates respectively form a guide channel with the side wall of the accommodating chamber, the pre-filter outlet is located between all of the guide plates, and a plurality of pre-filter sewage outlets are provided, and each of the pre-filter sewage outlets is correspondingly arranged on the bottom wall of the accommodating chamber and located in the corresponding guide channel.

[0012] Wherein, the guide assembly is located between the screen structure and the air outlet and sewage cover, and the guide assembly includes a guide frame and a plurality of guide blades. All the guide blades are arranged in a circular array on the periphery of the guide frame with the central axis of the guide frame as the axis, and all the guide blades are fixedly connected to the inner wall of the pre-filter cylinder.

[0013] Wherein, the impeller assembly includes a rotary drive member and an impeller arranged on the rotary drive member, the rotary drive member is arranged on the guide frame, the impeller is located in the accommodating cavity of the air outlet and sewage discharge cover and the impeller is located between all the guide plates.

[0014] Wherein, the impeller includes an impeller frame and a plurality of rotating blades, one end of the impeller frame is connected to the power output part of the rotating drive member, the other end of the impeller frame is located in the pre-filter air outlet and a gap is set between the impeller frame and the side wall of the pre-filter air outlet, and all the rotating blades are arranged in a circular array on the circumferential side of the impeller frame with the rotation axis of the impeller frame as the central axis.

[0015] Among them, the filter housing is provided with a filter dust exhaust port connected with the filter air inlet cavity, the filter dust exhaust port and the filter outlet pipe are respectively located at the opposite ends of the filter housing, a dust exhaust valve is arranged in the filter dust exhaust port, and a pressure sensor for detecting air pressure is arranged on the filter outlet pipe.

[0016] By adopting the above technical solution, the beneficial effects of the utility model are:

[0017] The hydrogen fuel cell system air filter provided by the utility model increases a pre-filter cover on the periphery of the filter element, installs a pre-filter on the filter inlet pipe, and utilizes the pre-filter and the pre-filter cover to perform double pre-filtration on the air entering the filter element, thereby reducing the filtering burden of the filter element to the greatest extent, thereby extending the service life of the filter element and reducing the user's use and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the air filter of the hydrogen fuel cell system of the utility model;

[0019] Figure 2 yes Figure 1 A cross-sectional view of

[0020] Figure 3 yes Figure 1 A schematic diagram of the structure of the middle air discharge cover;

[0021] In the figure: 1. filter housing; 11. filter cylinder; 111. mounting bracket; 12. filter outlet cover; 13. filter dust cover; 2. filter element; 21. filter outlet cavity; 22. main filter element; 23. safety filter element; 24. filter inlet cavity; 3. filter inlet pipe; 4. filter outlet pipe; 5. pre-filter; 51. pre-filter cylinder; 510. screen structure; 52. Rain cap cover; 53. Air outlet and sewage cover; 531. Pre-filter air outlet; 532. Pre-filter sewage outlet; 533. Pre-filter air outlet pipe; 534. Guide plate; 535. Guide channel; 54. Guide frame; 55. Guide blade; 56. Rotating drive member; 57. Impeller frame; 58. Rotating blade; 59. Dust exhaust valve; 6. Pre-filter cover; 7. Pressure sensor; 8. Clamp. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the utility model more clearly understood, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model and are not used to limit the utility model.

[0023] like Figures 1 to 3 As shown, this embodiment provides an air filter for a hydrogen fuel cell system, comprising a filter housing 1 and a filter element 2 arranged in the filter housing 1, the filter housing 1 is provided with a filter inlet pipe 3 and a filter outlet pipe 4, the filter element 2 is provided with a filter outlet cavity 21 connected to the filter outlet pipe 4, the filter inlet pipe 3 is connected with a pre-filter 5, the filter element 2 is sleeved with a cylindrical pre-filter cover 6, the pre-filter cover 6 and the filter housing 1 together form a filter inlet cavity 24 connected to the filter inlet pipe 3; the pre-filter 5 is used for performing a primary pre-filtration of the air; the pre-filter cover 6 is used for performing a secondary pre-filtration of the air that has been pre-filtered at the primary level, the filter element 2 is used for fine filtering of the air that has been pre-filtered at the secondary level, and the finely filtered air flows into the fuel cell engine through the filter outlet cavity 21 and the filter outlet pipe 4 for use by the fuel cell engine.

[0024] The hydrogen fuel cell system air filter in this embodiment adds a pre-filter cover 6 to the periphery of the filter element 2, installs a pre-filter 5 on the filter inlet pipe 3, and uses the pre-filter 5 and the pre-filter cover 6 to perform double pre-filtration on the air entering the filter element 2, thereby minimizing the filtering burden of the filter element 2, thereby extending the service life of the filter element 2 and reducing the user's use and maintenance costs.

[0025] The filter element 2 in this embodiment includes a main filter element 22 and a safety filter element 23 coaxially sleeved in the main filter element 22, the pre-filter cover 6 is coaxially sleeved outside the main filter element 22, and the inner cavity of the safety filter element 23 is the filter outlet cavity 21. By setting the filter element 2 in a structure in which the main filter element 22 and the safety filter element 23 are sleeved, not only can the safety filter element 23 protect the fuel cell engine from being damaged by impurities that suddenly enter when it is shut down, but also the main filter element 22 can be easily replaced separately, thereby maximizing the savings in the user's use and maintenance costs.

[0026] In order to make the filter element 2 have a larger filtering area, the main filter element 22 in this embodiment adopts a structural form of physical filtration and chemical filtration integrated design. An environment with high dust concentration often requires the main filter element 22 to have higher physical filtration performance. When the air filter is blocked, the physical filtration pressure sensor 7 will often prompt the user to replace the filter element 2 first, but at this time the chemical filtration performance of the main filter element 22 still exists. In order not to cause waste of resources, balance the life of physical filtration and chemical filtration, and extend the service life of the entire filter element 2, this embodiment adopts a pre-filter cover 6. By coaxially sleeved on the outside of the main filter element 22, the pre-filter cover 6 plays a role in pre-filtering protection of the main filter element 22, greatly extending the physical filtration performance of the main filter element 22, thereby extending the service life of the filter element 2, and further saving the user's use and maintenance costs.

[0027] The pre-filter cover 6 in this embodiment adopts a multi-layer stacking process technology, including primary filter cotton, medium-efficiency filter cotton and high-efficiency filter cotton stacked from the outside to the inside. Through the multi-layer filter cotton padding, the combination of different fiber formulas is accurately mixed to achieve a gradual change in efficiency layer. With the protection of the pre-filter cover 6, more than 70% of large dust particles are intercepted and accumulated in the pre-filter cover 6, so that the main filter element 22 is not easy to be blocked in a short time, and the service life of the main filter element 22 is extended. The pre-filter cover 6 has a small resistance, and the laboratory test resistance is less than 0.1kPa; the dust capacity is high, and the dust capacity after adding the pre-filter cover 6 is 2.5 times the dust capacity without adding the pre-filter cover 6. In actual use, the life of the main filter element 22 is also doubled. Due to the high cost of the main filter element 22, frequent replacement will bring high cost pressure. After adding the pre-filter cover 6, it is only necessary to maintain the pre-filter cover 6 according to the prompt of the pressure sensor 7 in the early stage to achieve the purpose of extending the life of the main filter element 22, until the chemical alarm device of the system prompts the user to replace the entire filter element 2. The pre-filter cover 6 also has the function of resisting water droplets. After a small amount of water droplets or water vapor enters the filter air inlet chamber 24, it is blocked by the pre-filter cover 6, aggregated into large droplets, and falls on the lower part of the filter housing 1. Finally, it can be discharged together with dust and impurities through the dust exhaust valve 59.

[0028] Specifically, the filter housing 1 includes a filter cylinder 11 with openings at both ends, a filter outlet cover 12 arranged at one end of the filter cylinder 11, and a filter dust cover 13 arranged at the other end of the filter cylinder 11; a filter inlet pipe 3 is arranged on the filter cylinder 11, and the axis of the filter inlet pipe 3 is perpendicular to the axis of the filter cylinder 11, and a filter outlet pipe 4 is arranged on the filter outlet cover 12, and the filter outlet pipe 4 is coaxially arranged with the filter cylinder 11; the main filter element 22 The main filter element 22 is coaxially sleeved in the filter cylinder 11, and the two ends of the main filter element 22 are respectively sealed and connected with the filter outlet cover 12 and the filter dust cover 13; the safety filter element 23 is coaxially sleeved in the main filter element 22 and the inner cavity of the safety filter element 23 corresponds to the filter outlet pipe 4, and the two ends of the safety filter element 23 are respectively sealed and connected with the main filter element 22 and the filter outlet cover 12; the pre-filter cover 6 is sleeved on the main filter element 22; the filter cylinder 11 is provided with an integrated mounting bracket 111 which is easy to install.

[0029] Since the dust removal efficiency of the rotary centrifugal pre-filter can stably reach more than 90%, and it has a simple structure and is easy to maintain, the pre-filter 5 in this embodiment adopts a rotary centrifugal pre-filter. The pre-filter 5 includes a pre-filter housing, a guide assembly fixedly arranged in the pre-filter housing, and an impeller assembly arranged on the guide assembly. The pre-filter housing is provided with a pre-filter air inlet, a pre-filter air outlet 531 and a pre-filter sewage outlet 532. The pre-filter air outlet 531 is connected to the filter inlet pipe 3. The guide assembly is used to guide the air entering from the pre-filter air inlet, and the impeller assembly is used to discharge impurities separated by centrifugation into the pre-filter sewage outlet 532.

[0030] The prefilter housing in this embodiment includes a prefilter cylinder 51 with openings at both ends, a rain cap cover 52 arranged at one end of the prefilter cylinder 51, and an air outlet and sewage cover 53 arranged at the other end of the prefilter cylinder 51. A screen structure 510 is arranged on the end of the prefilter cylinder 51 close to the rain cap cover 52. All meshes of the screen structure 510 together constitute the prefilter air inlet. The prefilter air outlet 531 and the prefilter sewage outlet 532 are both arranged on the air outlet and sewage cover 53. The setting of the screen structure 510 can remove larger impurities in the air before the air enters the prefilter 5, so as to reduce the wear of the prefilter 5; the setting of the rain cap cover 52 can prevent most rainwater from entering the prefilter 5, and the occasional water droplets entering will also be centrifugally separated and discharged from the prefilter sewage outlet 532.

[0031] In this embodiment, one end of the air outlet and sewage cover 53 is provided with a accommodating chamber connected to the inner cavity of the pre-filter cylinder 51, and the other end of the air outlet and sewage cover 53 is provided with a pre-filter outlet pipe 533, and the pre-filter outlet pipe 533 is connected to the filter inlet pipe 3 through a clamp 8, and the pre-filter outlet port 531 is opened on the bottom wall of the accommodating chamber and connects the accommodating chamber and the pre-filter outlet pipe 533; a plurality of guide plates 534 are provided on the bottom wall of the accommodating chamber, and all the guide plates 534 are arranged in a circular array with the axis of the air outlet and sewage cover 53 as the central axis, and all the guide plates 534 respectively form a guide channel 535 with the side wall of the accommodating chamber, the pre-filter outlet 531 is located between all the guide plates 534, and a plurality of pre-filter sewage outlets 532 are provided, and each pre-filter sewage outlet 532 is correspondingly arranged on the bottom wall of the accommodating chamber and located in the corresponding guide channel 535. The guide plate 534 and the guide channel 535 are provided to guide the impurities, thereby facilitating the impurities to be discharged into the pre-filter sewage outlet 532 .

[0032] The guide assembly in this embodiment is located between the screen structure 510 and the air outlet and sewage cover 53. The guide assembly includes a guide frame 54 and a plurality of guide blades 55. All guide blades 55 are arranged in a circular array around the guide frame 54 with the central axis of the guide frame 54 as the axis, and all guide blades 55 are fixedly connected to the inner wall of the pre-filter cylinder 51. By setting the guide assembly, the air entering the pre-filter 5 generates a rotating vortex between the pre-filter cylinder 51, the guide blades 55 and the guide frame 54, so that the centrifugal force generated by the vortex air is used to separate dust, dirt, insects, rain or snow from the air.

[0033] The impeller assembly in this embodiment includes a rotary drive member 56 and an impeller disposed on the rotary drive member 56. The rotary drive member 56 is disposed on the guide frame 54. The impeller is located in the accommodating cavity of the air outlet and sewage discharge cover 53 and between all the guide plates 534. The rotary drive member 56 drives the impeller to rotate and simultaneously cooperates with the vortex air to play the role of a blower, thereby realizing centrifugal separation of air and impurities. Impurities can be discharged from the pre-filter sewage discharge port 532, and the air without impurities enters the air filter.

[0034] The impeller in this embodiment includes an impeller frame 57 and a plurality of rotating blades 58, one end of the impeller frame 57 is connected to the power output portion of the rotary drive member 56, the other end of the impeller frame 57 is located in the pre-filter outlet 531 and a gap is set between the impeller frame 57 and the side wall of the pre-filter outlet 531, and all the rotating blades 58 are arranged in a circular array on the circumference of the impeller frame 57 with the rotation axis of the impeller frame 57 as the central axis. By arranging the impeller frame 57 in the pre-filter outlet 531 and setting a gap between the impeller frame 57 and the side wall of the pre-filter outlet 531, the flow speed of the air is increased.

[0035] In order to further increase the air flow rate, the pre-filter outlet 531 is configured as a cone in this embodiment. Meanwhile, the support plate on the impeller frame 57 is also designed as a trapezoidal structure that is wider at the top and narrower at the bottom to match the pre-filter outlet 531 .

[0036] Since the motor is very convenient to use and control, has the capabilities of self-starting, accelerating, braking, reversing, and stopping, and can meet various operating requirements, the rotary drive member 56 in this embodiment is preferably a motor.

[0037] In order to facilitate the removal of dust and impurities in the filter air inlet chamber 24, in this embodiment, a filter dust exhaust port connected to the filter air inlet chamber 24 is arranged on the filter dust exhaust cover 13 of the filter housing 1, and the filter dust exhaust port and the filter outlet pipe 4 are respectively located at opposite ends of the filter housing 1, and the filter outlet pipe 4 is arranged on the filter outlet cover 12. At the same time, a dust exhaust valve 59 is arranged in the filter dust exhaust port, and a pressure sensor 7 for detecting air pressure is arranged on the filter outlet pipe 4.

[0038] During operation, the air is pre-filtered at the primary level by the pre-filter 5, and then pre-filtered at the secondary level by the pre-filter cover 6. Finally, the filter element 2 performs fine filtering on the air pre-filtered at the secondary level. The finely filtered air enters the fuel cell engine through the filter outlet cavity 21 and the filter outlet pipe 4 to be used by the fuel cell engine. The hydrogen fuel cell system air filter performs double pre-filtering on the air entering the filter element 2 through the pre-filter 5 and the pre-filter cover 6, which reduces the filtering burden of the filter element 2 to the greatest extent, thereby extending the service life of the filter element 2 and reducing the user's use and maintenance costs.

[0039] An embodiment of the hydrogen fuel cell system air filter of the utility model is described in detail above. There are more embodiments that are not described here in detail. The utility model is not limited to the above specific implementation methods. Various changes made by ordinary technicians in this field based on the above conception without creative labor all fall within the protection scope of the utility model.

Claims

1. An air filter for a hydrogen fuel cell system, comprising a filter housing and a filter element disposed in the filter housing, wherein the filter housing is provided with a filter inlet pipe and a filter outlet pipe, and the filter element is provided with a filter outlet cavity connected to the filter outlet pipe, characterized in that: A pre-filter is connected to the filter inlet pipe, and a cylindrical pre-filter cover is mounted on the filter element. The pre-filter cover and the filter housing together form a filter inlet cavity connected to the filter inlet pipe; the pre-filter is used for performing a primary pre-filtration on the air; the pre-filter cover is used for performing a secondary pre-filtration on the air that has been pre-filtered at the primary level, and the filter element is used for fine filtering on the air that has been pre-filtered at the secondary level.

2. The hydrogen fuel cell system air filter according to claim 1, characterized in that: The filter element comprises a main filter element and a safety filter element coaxially sleeved inside the main filter element, the pre-filter cover is coaxially sleeved outside the main filter element, and the inner cavity of the safety filter element is the filter outlet cavity.

3. The air filter according to claim 2, characterized in that: The pre-filter cover comprises primary filter cotton, medium filter cotton and high efficiency filter cotton which are sequentially stacked from the outside to the inside.

4. The hydrogen fuel cell system air filter according to claim 1, characterized in that: The pre-filter includes a pre-filter housing, a flow guide assembly fixedly arranged in the pre-filter housing, and an impeller assembly arranged on the flow guide assembly. The pre-filter housing is provided with a pre-filter air inlet, a pre-filter air outlet and a pre-filter sewage outlet. The pre-filter air outlet is connected to the filter inlet pipe. The flow guide assembly is used to guide the air entering through the pre-filter air inlet, and the impeller assembly is used to discharge impurities separated by centrifugation into the pre-filter sewage outlet.

5. The hydrogen fuel cell system air filter according to claim 4, characterized in that: The pre-filter housing includes a pre-filter cylinder with openings at both ends, a rain cap cover arranged at one end of the pre-filter cylinder and an air outlet and sewage discharge cover arranged at the other end of the pre-filter cylinder, a screen structure is arranged on the end of the pre-filter cylinder close to the rain cap cover, all mesh holes of the screen structure together constitute the pre-filter air inlet, and the pre-filter air outlet and the pre-filter sewage discharge outlet are both arranged on the air outlet and sewage discharge cover.

6. The hydrogen fuel cell system air filter according to claim 5, characterized in that: One end of the air outlet and sewage cover is provided with a accommodating chamber connected with the inner cavity of the pre-filter cylinder, and the other end of the air outlet and sewage cover is provided with a pre-filter outlet pipe, and the pre-filter outlet port is opened on the bottom wall of the accommodating chamber and connects the accommodating chamber and the pre-filter outlet pipe; a plurality of guide plates are provided on the bottom wall of the accommodating chamber, all of the guide plates are arranged in a circular array with the axis of the air outlet and sewage cover as the central axis, and all of the guide plates respectively form a guide channel with the side wall of the accommodating chamber, the pre-filter air outlet is located between all of the guide plates, and a plurality of pre-filter sewage outlets are provided, and each of the pre-filter sewage outlets is correspondingly arranged on the bottom wall of the accommodating chamber and located in the corresponding guide channel.

7. The hydrogen fuel cell system air filter according to claim 6, characterized in that: The guide assembly is located between the screen structure and the air outlet and sewage cover, and includes a guide frame and a plurality of guide blades. All the guide blades are arranged in a circular array around the guide frame with the central axis of the guide frame as the axis, and all the guide blades are fixedly connected to the inner wall of the pre-filter cylinder.

8. The hydrogen fuel cell system air filter according to claim 7, characterized in that: The impeller assembly includes a rotary drive member and an impeller arranged on the rotary drive member, the rotary drive member is arranged on the guide frame, the impeller is located in the accommodating cavity of the air outlet and sewage discharge cover and the impeller is located between all the guide plates.

9. The hydrogen fuel cell system air filter according to claim 8, characterized in that: The impeller includes an impeller frame and a plurality of rotating blades, one end of the impeller frame is connected to the power output part of the rotating drive member, the other end of the impeller frame is located in the pre-filter air outlet and a gap is set between the impeller frame and the side wall of the pre-filter air outlet, and all the rotating blades are arranged in a circular array on the circumferential side of the impeller frame with the rotation axis of the impeller frame as the central axis.

10. The hydrogen fuel cell system air filter according to claim 1, characterized in that: The filter housing is provided with a filter dust exhaust port connected with the filter air inlet cavity. The filter dust exhaust port and the filter outlet pipe are respectively located at opposite ends of the filter housing. A dust exhaust valve is provided in the filter dust exhaust port. A pressure sensor for detecting air pressure is provided on the filter outlet pipe.

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