CN108067054B

CN108067054B - Air filter

Info

Publication number: CN108067054B
Application number: CN201711092219.9A
Authority: CN
Inventors: 近藤健元; 古居圣浩; 田中尚志
Original assignee: CKD Corp
Current assignee: CKD Corp
Priority date: 2016-11-16
Filing date: 2017-11-08
Publication date: 2021-07-20
Anticipated expiration: 2037-11-08
Also published as: JP2018079426A; DE102017126690A1; CN108067054A; JP6535647B2; DE102017126690B4

Abstract

Each magnetic sensor (31) of the air filter (10) is disposed on the display cylinder (22) in a state of being arranged in parallel to the spring guide (25) in a direction in which the supply hole (15) and the discharge hole (16) face each other. Accordingly, when an operator wants to visually confirm the piston (24) or the spring guide (25) displayed on the display cylinder (22) from directions different from both sides of the direction in which the supply hole (15) and the discharge hole (16) face each other, each magnetic sensor (31) does not become an obstacle. Therefore, even if the air filter (10) is provided with the magnetic sensor (31), the visual confirmation of the piston (24) or the spring guide (25) displayed on the display cylinder (22) can be ensured.

Description

Air filter

Technical Field

The present invention relates to an air filter provided with an indicator for detecting clogging of a filter element.

Background

A filter element is housed in the main body of the air filter. A supply hole and a discharge hole are formed in the body. The air supplied into the main body from the supply hole is discharged from the discharge hole after passing through the filter element in the main body. Foreign matter such as dust contained in the air is filtered when the air passes through the filter element. The air in the state where the foreign matter is removed is discharged from the discharge hole.

A supply pipe is connected to the supply hole. A supply-side pneumatic device that supplies air to the supply hole via a supply pipe is disposed at a position opposite to the supply hole in the air filter. A discharge pipe is connected to the discharge hole. A discharge-side air-moving device is disposed at a position of the air filter facing the discharge hole, and air discharged from the discharge hole flows into the discharge-side air-moving device through a discharge pipe.

Among such air filters, there is an air filter provided with an indicator (clogging detection device) for detecting clogging of a filter element. The indicator detects clogging of the filter element based on a pressure difference between a primary pressure, which is an air pressure in the main body before passing through the filter element, and a secondary pressure, which is an air pressure in the main body after passing through the filter element.

As an example, the indicator described in japanese patent No. 4504733 is configured such that a first display member and a second display member colored in different colors are supported in a transparent display tube so as to be movable relative to each other, and the second display member is covered with the first display member based on a pressure difference between a primary pressure and a secondary pressure. For example, when the filter element is clogged, a colored green color on the second display member is displayed on the display cartridge. When the filter element is clogged and the pressure difference between the primary pressure and the secondary pressure becomes large, the first display member moves so as to cover the second display member due to the pressure difference, and as a result, the red color colored on the first display member is displayed on the display tube. Therefore, in the indicator of japanese patent No. 4504733, the operator can grasp the clogging degree of the filter element by visually checking the color of the first display member or the second display member displayed on the display cylinder.

As another example, a jam detector described in japanese unexamined patent publication No. 4-14116 includes: a piston of a magnet that moves according to a pressure difference between the primary pressure and the secondary pressure; and a plurality of magnetic sensors arranged in a row in the moving direction of the piston, for detecting the magnetic force of the piston. In this clogging detection device, the degree of clogging of the filter element is grasped based on a detection signal obtained by detecting the magnetic force of the piston by the magnetic sensor.

For example, the following is also considered: in the indicator described in japanese patent No. 4504733, by further providing a piston having a magnet and a plurality of magnetic sensors as described in japanese unexamined patent publication No. hei 4-14116, the degree of clogging of the filter element can be grasped based on not only visual confirmation of the color of the first display member or the second display member displayed on the display cylinder but also a detection signal detected by the magnetic force of the magnetic sensor on the piston. In this case, the clogging degree of the filter element can be grasped more accurately. However, in this case, depending on the place where the magnetic sensor is installed, the magnetic sensor becomes an obstacle, and it may be difficult to visually confirm the color of the first display member or the second display member displayed on the display tube.

Disclosure of Invention

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an air filter capable of ensuring visibility of a display member displayed on a display cylinder even in a configuration including a magnetic sensor.

An air filter for solving the above problems includes: a body that houses a filter element; a supply hole and a discharge hole formed in the body; and an indicator that detects clogging of the filter element based on a pressure difference between a primary pressure that is an air pressure in the main body before passing through the filter element and a secondary pressure that is an air pressure in the main body after passing through the filter element, the indicator including: a transparent display tube; a display member supported in the display cylinder so as to be movable relative thereto; a magnet that moves based on a pressure difference between the primary pressure and the secondary pressure; and a magnetic sensor that detects a magnetic force of the magnet, wherein the display member is movable based on a pressure difference between the primary pressure and the secondary pressure, the display member includes the magnet, the supply hole and the discharge hole are arranged to face each other in a direction orthogonal to a moving direction of the magnet, and openings of the supply hole and the discharge hole face opposite sides to each other, and the magnetic sensor is arranged in the display tube in a state of being aligned with the display member in the direction in which the supply hole and the discharge hole face each other.

In the air filter, a holder for holding the magnetic sensor may be integrally formed with the display cylinder.

In the air filter, the magnetic sensor may be one of two magnetic sensors provided in the indicator, and the two magnetic sensors may be disposed in the display cylinder so that magnetic force detection positions of the magnets of the two magnetic sensors are different in a moving direction of the magnets.

In the air filter described above, the magnetic sensor may be adjustable in position in the moving direction of the magnet.

In the air filter, the display cylinder may have a scale that is paired with a magnetism detection position of the magnet in the magnetic sensor.

In the air filter, the magnetic sensor may include a light emitting unit that emits light based on detection of a magnetic force of the magnetic sensor with respect to the magnet.

According to the present invention, even in a configuration including a magnetic sensor, visual confirmation of a display member displayed on a display tube can be ensured.

Drawings

Fig. 1 is a longitudinal sectional view of an air filter in an embodiment of the present invention.

Fig. 2 is a perspective view showing an indicator and a flow channel forming body of the air filter of fig. 1.

Fig. 3 is a longitudinal sectional view of the indicator.

Fig. 4 is a longitudinal sectional view of the indicator.

Fig. 5 is an enlarged cross-sectional view showing a state before the magnetic sensor of the indicator is fixed to the display tube.

Fig. 6 is an enlarged cross-sectional view showing a state where the magnetic sensor is fixed to the display tube.

Fig. 7 is a front view of the indicator showing the scale.

Fig. 8 is a side view of the indicator showing the light emitting section.

Detailed Description

Hereinafter, an embodiment of the present invention in which an air filter is embodied will be described with reference to fig. 1 to 8.

As shown in fig. 1, the main body 11 of the air filter 10 includes: a cylindrical element case 13 that houses the cylindrical filter element 12; and a rectangular block-shaped flow channel forming body 14 attached to an end portion of the element case 13.

A supply hole 15 is formed in one side surface of the flow path forming body 14. A discharge hole 16 is formed in the other side surface of the flow passage forming body 14. The supply hole 15 communicates with a space inside the filter element 12 in the element case 13. The discharge hole 16 communicates with a space outside the filter element 12 in the element case 13.

The air supplied from the supply hole 15 passes through the filter element 12 from the inside of the filter element 12, flows to the space outside the filter element 12 in the element case 13, and is discharged from the discharge hole 16. Foreign matter such as dust contained in the air is filtered when the air passes through the filter element 12. The air in the state where the foreign substances are removed is discharged from the discharge hole 16.

As shown in fig. 2, the indicator 20 is attached to the upper surface 14a of the flow passage forming body 14, and the upper surface 14a is an end surface of the flow passage forming body 14 on the side opposite to the element case 13. The indicator 20 detects clogging of the filter element 12 based on a pressure difference between a primary pressure, which is an air pressure in the main body 11 before passing through the filter element 12, and a secondary pressure, which is an air pressure in the main body 11 after passing through the filter element.

The indicator 20 has a rectangular block-shaped base 21, and the base 21 is attached to the upper surface 14a of the flow channel forming body 14. The base 21 is attached to the flow channel forming body 14 by a plurality of screws B1. A recess 21a is formed in an end surface of the base 21 on the side opposite to the flow channel forming body 14. The indicator 20 has a display tube 22, and the display tube 22 is attached to the base 21 in a state of being fitted into the recess 21a of the base 21. The display tube 22 is formed of a transparent synthetic resin. The display cylinder 22 is attached to the base 21 by a plurality of screws B2.

As shown in fig. 3, the space between the concave portion 21a of the base 21 and the display tube 22 is sealed by the sealing member 23. The base 21 has a piston housing recess 21 b. The piston housing recess 21b is open at the center of the bottom surface 211a of the recess 21a of the base 21, and extends linearly from the recess 21a toward the upper surface 14a of the flow channel forming body 14.

A guide recess 22a communicating with the piston housing recess 21b is formed in the display cylinder 22. The diameter of the piston housing recess 21b is the same as that of the guide recess 22 a. A cylindrical piston 24 is accommodated in the piston accommodating recess 21 b. The piston 24 is colored red. A circular hole-shaped insertion recess 24a is formed in the center of the piston 24. In addition, a communication hole 24b communicating with the insertion recess 24a is formed in the piston 24. The communication hole 24b extends from the insertion recess 24a in the radial direction of the piston 24, and opens on the outer peripheral surface of the piston 24. The piston 24 is capable of reciprocating within the piston housing recess 21b and the guide recess 22 a.

A spring guide 25 is accommodated in the guide recess 22 a. The spring guide 25 is colored green. The spring guide 25 has a disk-shaped bottom portion 25a and a columnar protruding portion 25b protruding from the center of the bottom portion 25a toward the piston 24. The protruding portion 25b can be inserted into the insertion recess 24a of the piston 24.

Further, a spring member 26 is provided between the spring guide 25 and the piston 24, and the spring member 26 biases the piston 24 toward the bottom surface 211b of the piston housing recess 21 b. One end of the spring member 26 is supported by the bottom 25a of the spring guide 25, and the other end of the spring member 26 is supported by the bottom surface of the insertion recess 24a of the piston 24. The piston 24 and the spring guide 25 are display members that are relatively movably supported in the display cylinder 22 and are colored in different colors.

The piston 24 includes an annular magnet 27. The magnet 27 is attached to the outer peripheral surface of the end of the piston 24 on the display cylinder 22 side. Therefore, the piston 24 includes the magnet 27 as a magnet. The magnet 27 was colored yellow.

As shown in fig. 4, the piston 24 can move in such a manner as to cover the protrusion 25b of the spring guide 25 based on the pressure difference between the primary pressure and the secondary pressure. Therefore, the magnet 27 moves together with the piston 24 based on the pressure difference between the primary pressure and the secondary pressure.

An annular seal member 28 is attached to the outer peripheral surface of the end portion of the piston 24 on the side opposite to the display cylinder 22. The sealing member 28 seals between the outer peripheral surface of the piston 24 and the inner peripheral surface of the piston housing recess 21 b. The sealing member 28 divides the interior of the piston housing recess 21b and the guide recess 22a into a primary pressure operation chamber 29a on the bottom surface 211b side of the piston housing recess 21b with respect to the sealing member 28 and a secondary pressure operation chamber 29b on the guide recess 22a side with respect to the sealing member 28.

As shown in fig. 1, the air cleaner 10 includes a primary pressure supply passage 30a, and the primary pressure supply passage 30a penetrates the flow channel forming body 14 and the base 21 to communicate the supply hole 15 with the primary pressure operation chamber 29 a. The air cleaner 10 further includes a secondary pressure supply passage 30b, and the secondary pressure supply passage 30b penetrates the flow channel forming body 14 and the base 21 to communicate the discharge hole 16 with the secondary pressure acting chamber 29 b. The air in the main body 11 before passing through the filter element 12 is supplied from the supply hole 15 to the primary pressure acting chamber 29a via the primary pressure supply passage 30 a. The air in the main body 11 having passed through the filter element 12 is supplied from the discharge hole to the secondary pressure operation chamber 29b through the secondary pressure supply passage 30 b.

The supply port 15 and the discharge port 16 are arranged to face each other in a direction orthogonal to the moving direction (the direction indicated by the arrow Z1 in fig. 1) of the piston 24 (magnet 27), and their respective openings face opposite sides to each other.

The indicator 20 has two magnetic sensors 31, and the magnetic sensors 31 detect the magnetic force of the magnet 27. Each magnetic sensor 31 is electrically connected to the control device S1 via a wire R1. Two holding portions 22b for holding the magnetic sensors 31 are integrally formed on the display tube 22. Each holding portion 22b is a concave portion linearly extending from a surface 22c of the display tube 22 on the opposite side to the base 21 toward the base 21. The two holding portions 22b are disposed on both sides sandwiching the spring guide 25 in the direction in which the supply hole 15 and the discharge hole 16 face each other, that is, in the direction indicated by the arrow X1 in fig. 1. Therefore, each magnetic sensor 31 is disposed on the display cylinder 22 in a state of being aligned with the spring guide 25 in the direction of the arrow X1.

As shown in fig. 3, each magnetic sensor 31 is formed with a female screw hole 31a extending in the direction of arrow X1. Screw insertion portions 22h are formed on both side surfaces 22d of the display cylinder 22 in the direction of the arrow X1, and the screw insertion portions 22h communicate with the inside of the respective holding portions 22 b. The screw insertion portions 22h are disposed at positions shifted from each other in the moving direction of the piston 24. One of the screw insertion portions 22h (the screw insertion portion 22h on the right side in fig. 3) is disposed at a position closer to the base 21 in the moving direction of the piston 24 than the other screw insertion portion 22h on the left side in fig. 3.

The magnetic sensor 31 is disposed in each of the holding portions 22b so that the female screw hole 31a faces the screw insertion portion 22 h. One of the two magnetic sensors 31 is disposed in the holding portion 22b such that the female screw hole 31a faces one of the two screw insertion portions 22 h. The other of the two magnetic sensors 31 is disposed in the holding portion 22b such that the female screw hole 31a faces the other of the two screw insertion portions 22 h.

As shown in fig. 5, the screw 32 passes through the screw insertion portion 22h, is screwed into the female screw hole 31a, passes through the female screw hole 31a, and the tip of the screw 32 abuts against the inner surface of the holding portion 22b on the side opposite to the screw insertion portion 22 h.

As shown in fig. 6, when the screw 32 is further screwed in a state where the tip end of the screw 32 abuts against the inner surface of the holding portion 22b on the opposite side to the screw insertion portion 22h, the magnetic sensor 31 is pressed against the inner surface of the holding portion 22b on the screw insertion portion 22h side due to the reaction force of screwing in of the screw 32. Thereby, the magnetic sensor 31 is fixed in a state of being positioned in the holding portion 22 b. Further, the magnetic sensor 31 can adjust the position in the moving direction of the piston 24 by adjusting the screwing position of the screw 32 in the moving direction of the piston 24.

As shown in fig. 7, the display cylinder 22 has a plurality of scale marks 22e, and the scale marks 22e are paired with the magnetism detection position of the magnet 27 in the magnetic sensor 31. In the present embodiment, each magnetic sensor 31 has a mark 31b at the magnetic force detection position of the magnet 27.

In the present embodiment, the two magnetic sensors 31 are disposed in the display cylinder 22 so that the magnetic force detection positions of the magnets 27 of the two magnetic sensors 31 are different in the moving direction of the piston 24. The magnetic force detection position of one magnet 27 of the two magnetic sensors 31 is disposed at a position closer to the base 21 in the moving direction of the piston 24 than the magnetic force detection position of the other magnet 27 of the two magnetic sensors 31.

As shown in fig. 8, the magnetic sensor 31 includes a light emitting portion 31c, and the light emitting portion 31c emits light based on the detection of the magnetic force with respect to the magnet 27 in the magnetic sensor 31. The light emitting unit 31c emits light when the magnetic sensor 31 detects the magnetic force of the magnet 27.

Next, the operation of the present embodiment will be described.

When the filter element 12 is not clogged, the pressure difference between the primary pressure and the secondary pressure is small, and therefore, as shown in fig. 3, the piston 24 is in a state of abutting against the bottom surface 211b of the piston accommodating recess 21b by the biasing force of the spring member 26. At this time, the yellow color of the magnet 27 and the red color of the piston 24 are not displayed on the display cylinder 22, but the green color of the spring guide 25 is displayed.

When the filter element 12 is clogged, the secondary pressure is reduced compared to the primary pressure, and the pressure difference between the primary pressure and the secondary pressure becomes large, so that the pressure of the secondary pressure operation chamber 29b is reduced, and the piston 24 moves toward the bottom 25a of the spring guide 25 against the biasing force of the spring member 26 by the pressure of the primary pressure operation chamber 29a, as shown in fig. 4. Then, the piston 24 moves in the guide recess 22a so as to cover the protruding portion 25b of the spring guide 25, and the protruding portion 25b is covered by the piston 24 in order from the piston housing recess 21b side. Then, first, the yellow color of the magnet 27 is displayed on the display cylinder 22. The yellow color of the magnet 27 is displayed on the display cylinder 22, indicating that the filter element 12 is ready for replacement.

At this time, the magnetic force of the magnet 27 is detected by the first magnetic sensor 31, which is one of the two magnetic sensors 31. The detection information detected by the first magnetic sensor 31 is transmitted to the control device S1 via the wire R1. When the first magnetic sensor 31 detects the magnetic force of the magnet 27, a signal for causing the light emitting unit 31c of the first magnetic sensor 31 to emit light is sent from the control device S1 to the light emitting unit 31c, and the light emitting unit 31c emits light. The state in which the light emitting portion 31c of the first magnetic sensor 31 emits light in this way indicates that the filter element 12 is ready for replacement.

When the clogging of the filter element 12 further progresses and the secondary pressure further drops compared with the primary pressure so that the pressure difference between the primary pressure and the secondary pressure becomes further large, the piston 24 moves further toward the bottom 25a of the spring guide 25, and the red color of the piston 24 is displayed on the display cylinder 22. The red state of the plunger 24 displayed on the display cartridge 22 indicates that the filter element 12 is in a replacement-requiring state.

At this time, the second magnetic sensor 31, which is the other of the two magnetic sensors 31, detects the magnetic force of the magnet 27. The detection information detected by the second magnetic sensor 31 is transmitted to the control device S1 via the wire R1. The control device S1 monitors the clogging degree of the filter element 12 based on the detection signals sent from the first and second magnetic sensors 31. When the second magnetic sensor 31 detects the magnetic force of the magnet 27, a signal for causing the light emitting unit 31c of the second magnetic sensor 31 to emit light is sent from the control device S1 to the light emitting unit 31c, and the light emitting unit 31c emits light. The state in which the light emitting portion 31c of the second magnetic sensor 31 is emitting light indicates that the filter element 12 is in a replacement-required state.

Therefore, the operator can grasp the clogging degree of the filter element 12 by visually checking the color displayed on the display cylinder 22. Further, the operator can grasp the clogging degree of the filter element 12 by checking the monitoring data of the control device S1 that monitors the clogging degree of the filter element 12 based on the detection signal transmitted from each magnetic sensor 31. The operator can visually confirm whether or not the light emitting portions 31c of the two magnetic sensors 31 emit light, respectively, to thereby grasp the clogging degree of the filter element 12.

The following effects can be obtained in the above embodiment.

(1) However, a supply pipe, not shown, is connected to the supply hole 15, and a supply-side pneumatic device, not shown, is disposed at a position facing the supply hole 15 in the air filter 10, and supplies air to the supply hole 15 via the supply pipe. Further, a discharge pipe, not shown, is connected to the discharge hole 16, a discharge-side air-moving device, not shown, is disposed at a position of the air filter 10 facing the discharge hole 16, and air discharged from the discharge hole 16 flows into the discharge-side air-moving device through the discharge pipe. In this way, since the air filter 10 is often provided with devices on both sides in the direction in which the supply hole 15 and the discharge hole 16 face each other, when the operator wants to visually check the piston 24 or the spring guide 25 displayed on the display cylinder 22, the air filter is often performed from directions different from both sides in the direction in which the supply hole 15 and the discharge hole 16 face each other.

In the present embodiment, each magnetic sensor 31 is disposed in the display cylinder 22 in a state of being aligned with the spring guide 25 in the direction in which the supply hole 15 and the discharge hole 16 face each other. Accordingly, when the operator wants to visually check the piston 24 or the spring guide 25 displayed on the display cylinder 22 from directions different from both sides of the direction in which the supply hole 15 and the discharge hole 16 face each other, each magnetic sensor 31 does not become an obstacle. Therefore, even if the air cleaner 10 is configured to include the magnetic sensor 31, the visual confirmation of the piston 24 or the spring guide 25 displayed on the display cylinder 22 can be ensured.

(2) A holding portion 22b for holding the magnetic sensor 31 is integrally formed on the display tube 22. Accordingly, the configuration of the air cleaner 10 can be simplified as compared with a case where the holding portion for holding the magnetic sensor 31 is provided on the display cylinder 22 as a member different from the display cylinder 22.

(3) The two magnetic sensors 31 are disposed in the display cylinder 22 so that the magnetic force detection positions of the magnets 27 of the two magnetic sensors 31 are different in the moving direction of the piston 24. Accordingly, the clogging degree of the filter element 12 can be grasped in two stages.

(4) The magnetic sensor 31 can adjust the position in the moving direction of the piston 24. Accordingly, the detection condition of clogging can be finely adjusted according to the type of the filter element 12 and the like, and the replacement target of the filter element 12 can be appropriately changed.

(5) The display cylinder 22 has a plurality of scale marks 22e, and the scale marks 22e are paired with the magnetic force detection position of the magnet 27 in the magnetic sensor 31. Accordingly, the detection condition for clogging of the filter element 12 can be easily adjusted.

(6) The magnetic sensor 31 includes a light emitting unit 31c, and the light emitting unit 31c emits light based on the detection of the magnetic force of the magnet 27 in the magnetic sensor 31. Accordingly, the operator can visually confirm whether or not each of the light emitting portions 31c emits light, thereby grasping the clogging degree of the filter element 12. In addition, even in a dark place where the air filter 10 is installed, the clogging state of the filter element 12 can be grasped.

(7) According to the present embodiment, the operator can grasp the clogging degree of the filter element 12 even from a position away from the air cleaner 10 by checking the monitoring data of the control device S1 that monitors the clogging degree of the filter element 12 based on the detection signal transmitted from each magnetic sensor 31. Further, the operator can also grasp the clogging degree of the filter element 12 by visually checking the color displayed on the display cylinder 22. The operator can also grasp the degree of clogging of the filter element 12 by visually checking whether or not the light emitting portions 31c of the two magnetic sensors 31 emit light, respectively.

The above embodiment may be modified as follows.

In the embodiment, the holding portion for holding the magnetic sensor 31 may be a member different from the display tube 22.

In the embodiment, the indicator 20 may have only one magnetic sensor 31.

In the embodiment, the magnetic sensor 31 may be configured such that the position thereof cannot be adjusted in the moving direction of the piston 24.

In the embodiment, the display cylinder 22 may be configured without the scale 22 e.

In the embodiment, the magnetic sensor 31 may not include the light emitting unit 31 c.

In the embodiment, the colors of the piston 24, the spring guide 25, and the magnet 27 may be changed as appropriate.

In the embodiment, the magnet 27 may be formed without coloring.

In the embodiment, the magnet 27 may not be provided in the piston 24, and the piston 24 itself may be a magnet.

In the embodiment, the base 21 and the display cylinder 22 may be attached to the flow channel forming body 14 by a common screw.

In the embodiment, the magnetic sensor 31 may be disposed at the following positions: when the filter element 12 is not clogged and the magnet 27 moves, the magnetic sensor 31 does not detect the magnetic force of the magnet 27 and the light emitting portion 31c emits light, and when the filter element 12 is clogged and the magnet 27 moves, the light emitting portion 31c turns off the light.

In the embodiment, the light emitting unit 31c may be configured to turn off the light when the magnetic force of the magnet 27 in the magnetic sensor 31 is detected.

Description of the reference numerals

10: an air filter; 11: a main body; 12: a filter element; 15: a supply hole; 16: a discharge hole; 20: an indicator; 22: a display cartridge; 22 b: a holding section; 22 e: calibration; 24: a piston as a display member; 25: a spring guide as a display member; 27: a magnet as a magnet; 31: a magnetic sensor; 31 c: a light emitting section.

Claims

1. An air filter is provided with:

a body that houses a filter element;

a supply hole and a discharge hole formed in the body; and

an indicator that detects clogging of the filter element based on a pressure difference between a primary pressure that is an air pressure in the main body before passing through the filter element and a secondary pressure that is an air pressure in the main body after passing through the filter element,

the indicator has:

a transparent display tube;

a piston as a display member supported in the display cylinder so as to be relatively movable, and reciprocating in accordance with a pressure difference between the primary pressure and the secondary pressure;

a magnet attached to the piston and moving together with the piston based on a pressure difference between the primary pressure and the secondary pressure; and

two magnetic sensors that detect magnetic forces of the magnets,

the display member is movable in an axial direction of the filter element based on a pressure difference between the primary pressure and the secondary pressure, and includes the magnet,

the supply hole and the discharge hole are arranged to face each other in a direction orthogonal to the moving direction of the magnet, and the openings of the supply hole and the discharge hole face each other in opposite directions,

the two magnetic sensors are arranged in the display tube in a state of being arranged in parallel with the display member interposed therebetween in a direction in which the supply hole and the discharge hole are opposed to each other,

two holding portions for holding the two magnetic sensors are integrally formed on the display cylinder,

a female screw hole is formed in each of the magnetic sensors,

screw insertion portions are formed on the side surfaces of the display cylinder, and each screw insertion portion communicates with the corresponding holding portion,

each of the magnetic sensors is disposed in the holding portion so that the female screw hole faces the screw insertion portion, a screw is screwed into the female screw hole after passing through the screw insertion portion and penetrates the female screw hole, and a tip end of the screw abuts against an inner surface of the holding portion on a side opposite to the screw insertion portion, whereby each of the magnetic sensors is fixed in a state of being positioned in the holding portion,

each of the magnetic sensors is adjustable in position in the moving direction of the piston by adjusting the screw-in position of the screw in the moving direction of the piston.

2. The air filter according to claim 1, wherein the two magnetic sensors are disposed in the display cylinder so that magnetic force detection positions of the magnets of the two magnetic sensors are different in a moving direction of the magnets.

3. The air filter according to claim 1 or claim 2, wherein the display cylinder has a scale that is paired with a magnetism detection position of the magnet of each of the two magnetic sensors.

4. The air filter according to claim 1 or claim 2, wherein the magnetic sensor has a light-emitting portion that emits light based on detection of the magnetic force with respect to the magnet in the magnetic sensor.

5. The air filter according to claim 3, wherein the magnetic sensor has a light emitting portion that emits light based on detection of the magnetic force with respect to the magnet in the magnetic sensor.