Waterproof ventilation plug, common brake cylinder and parking brake cylinder

Abstract

The invention discloses a waterproof ventilation plug which comprises a ventilation valve body, a positioning ring and a flat opening sealing valve body. The ventilation valve body is internally provided with a ventilation space and a containing cavity. The containing cavity contains a positioning ring which is provided with a hollow cavity. And the flat-opening sealing valve body comprises a wedge-shaped part and a mounting part. And the mounting part is mounted between the vent valve body and the positioning ring. The wedge portion includes at least two inclined surfaces, and an opening is formed in a direction in which the inclined surfaces intersect. The opening is in a normally-closed state, an opening is formed in the side away from the intersection direction of the inclined faces, and the inclined faces define a valve body cavity. The valve body cavity communicates with the ventilation space to form an air plug cavity. The ventilation plug exhausts air in a one-way mode, air can only be exhausted to the atmosphere along the air plug cavity, water cannot enter the brake cylinder from the outside atmosphere along with the air through the ventilation plug, and the situation that the water entering the brake cylinder is solidified on the cylinder wall, the sealing performance of the brake cylinder sealing cavity is seriously affected, and normal braking cannot be achieved after air leakage of the brake cylinder sealing cavity is avoided.

Description

Technical Field

[0001] The invention relates to the field of piston brake cylinders, and in particular to a waterproof vent plug. Background Art

[0002] The non-sealed chamber of the piston brake cylinder exchanges gas with the external atmosphere during the brake release process. Under the harsh working conditions of snow and ice on the brake cylinder, the existing vent plug is prone to absorb water while absorbing air in the non-sealed chamber; the water inhaled into the non-sealed chamber will cause air leakage in the sealed chamber after freezing, affecting the function of the brake cylinder.

[0003] Patent CN108426044B discloses a double valve body core tube valve, in which the valve core tube wrapped in the inner cavity of the outer valve body is a sleeve tube coaxially penetrating the valve body, the inner cavity of the valve body, and the sleeve tube of the valve body; there is an axial partition in the middle of the valve core tube, and the axially adjacent sides of the partition are at least one radial flow hole of the input section and the output section respectively; the annular valve core surrounding the partition and the sleeve tube and the annular valve seat at the throat of at least one sleeve tube of the sleeve tube form a sealing pair, and under the action of potential energy in two directions, the valve body moves axially back and forth in the inner cavity of the outer valve body to realize opening and closing and function conversion. However, the double valve body core tube valve cannot solve the problem that water in the external atmosphere enters the non-sealed cavity through the core tube valve.

[0004] In view of the above technical problems, the present invention is specially introduced. Summary of the invention

[0005] The main purpose of the present invention is to provide a one-way ventilated waterproof vent plug, which is closed when a non-sealed cavity is inhaled, thereby preventing air and water from entering the non-sealed cavity through the waterproof vent plug.

[0006] In order to achieve the above object, the present invention provides a waterproof vent plug, comprising:

[0007] A vent valve body, the vent valve body having a vent space and a receiving cavity inside;

[0008] A positioning ring, which is installed in the accommodating cavity and has a hollow cavity;

[0009] A flat-mouth sealing valve body, which includes a wedge-shaped portion and a mounting portion, wherein the mounting portion is mounted between the vent valve body and the positioning ring; the wedge-shaped portion includes two inclined surfaces, forming an opening in the direction where the inclined surfaces intersect, the opening is in a normally closed state, and forming an open opening on the side away from the intersection direction of the inclined surfaces, the inclined surfaces enclose forming a valve body cavity; the valve body cavity is connected to the ventilation space to form an air plug cavity.

[0010] The following is a further optimization of the above scheme by the present invention:

[0011] Furthermore, the wedge-shaped portion also includes two parallel horizontal planes, which are arranged at the ends where the inclined planes intersect and extend along the direction where the inclined planes intersect to form an extended closing portion of the opening.

[0012] Furthermore, the positioning ring includes a mounting groove, and the mounting portion of the flat-mouth sealing valve body includes an annular protrusion, which is accommodated in the mounting groove of the positioning ring.

[0013] Furthermore, the mounting portion of the flat-mouth sealing valve body also includes an annular groove, which can accommodate a sealing ring to enhance the air tightness of the waterproof vent plug.

[0014] Furthermore, the positioning ring also includes a filter surface, which is arranged on a side opposite to the installation groove, and a plurality of filter holes are arranged on the filter surface.

[0015] Furthermore, the waterproof vent plug also includes an elastic retaining ring, which is installed in the accommodating cavity of the vent valve body and fits with the filtering surface of the positioning ring, and the elastic retaining ring fixes the positioning ring.

[0016] Furthermore, the waterproof vent plug also includes a first vent plug protective cover, which includes a first mounting portion and a first exhaust portion, the first mounting portion cooperates with the vent valve body, the axis of the first mounting portion is parallel to the axis of the first exhaust portion, and the first exhaust portion extends the exhaust port of the waterproof vent plug.

[0017] Furthermore, the waterproof vent plug also includes a second vent plug protective cover, and the second vent plug protective cover also includes a second mounting portion and a second exhaust portion. The second mounting portion cooperates with the vent valve body, and the axis of the second mounting portion intersects with the axis of the second exhaust portion, and the axis of the second exhaust portion is horizontally inclined downward, and the second exhaust portion extends the exhaust port of the waterproof vent plug.

[0018] According to another aspect of the present invention, a commonly used brake cylinder is also provided, including a first piston, one side of the first piston is a first sealed chamber, and the other side is a first non-sealed chamber, the brake cylinder adopts the above-mentioned waterproof vent plug, the first non-sealed chamber is connected to the air plug chamber, the first piston is retracted when the brake cylinder is relieved, the first piston moves in the direction away from the first non-sealed chamber, so that the cavity space of the first non-sealed chamber becomes larger, the pressure of the first non-sealed chamber is less than the external atmospheric pressure of the air plug chamber, and the flat-mouthed sealing valve body is tightly closed; the first piston is pushed out when the brake cylinder brakes, the first piston moves in the direction close to the first non-sealed chamber, the cavity space of the first non-sealed chamber becomes smaller, so that the pressure of the first non-sealed chamber is greater than the external atmospheric pressure of the air plug chamber, and the flat-mouthed sealing valve body is opened.

[0019] According to another aspect of the present invention, there is also provided a parking brake cylinder, comprising a second piston, one side of the second piston being a second sealed chamber, and the other side being a second non-sealed chamber, characterized in that: the brake cylinder adopts the above-mentioned waterproof vent plug, the second non-sealed chamber is connected to the air plug chamber, the second piston is retracted when the parking brake cylinder is released, the second piston moves in the direction away from the second non-sealed chamber, the cavity space of the second non-sealed chamber becomes larger, so that the pressure of the second non-sealed chamber is less than the external atmospheric pressure of the air plug chamber, and the flat-mouthed sealing valve body is tightly closed; the second piston is pushed out when the brake cylinder brakes, the second piston moves in the direction close to the second non-sealed chamber, the cavity space of the second non-sealed chamber becomes smaller, so that the pressure of the second non-sealed chamber is greater than the external atmospheric pressure of the air plug chamber, and the flat-mouthed sealing valve body is opened.

[0020] By applying the technical solution of the present invention, at least the following beneficial effects are achieved:

[0021] 1. The present invention adopts a normally closed sealing structure based on rubber elasticity, which solves the problem that water in the external atmosphere enters the non-sealed cavity of the brake cylinder through the waterproof vent plug;

[0022] 2. The waterproof vent plug is a one-way exhaust, and the gas can only be discharged to the atmosphere along the air plug cavity, so that water cannot enter the brake cylinder from the outside atmosphere through the waterproof vent plug with air;

[0023] 3. The flat-mouth sealing valve body has an extended closing part, which improves the sealing performance of the opening;

[0024] 4. The positioning ring includes a filtering surface, which can prevent large particles of sand and stone from getting stuck in the opening of the flat-mouth sealing valve body, and prevent the opening from becoming normally open due to blockage by sand and stone. The positioning ring and the vent plug protective cover constitute graded filtration;

[0025] 5. The first vent plug protective cover and the second vent plug protective cover extend the exhaust port of the waterproof vent plug, thereby reducing the probability of the flat-mouth sealing valve body being covered by ice and snow under severe working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 A schematic diagram of a common brake cylinder using a waterproof vent plug is shown;

[0028] Figure 2 The waterproof vent plug of the common brake cylinder is shown;

[0029] Figure 3 A schematic diagram of a parking brake cylinder with a waterproof vent plug is shown;

[0030] Figure 4 A waterproof breather plug with a parking brake cylinder is shown;

[0031] Figure 5 A schematic diagram of air suction of a waterproof vent plug is shown;

[0032] Figure 6 A schematic diagram of air intake of a waterproof vent plug is shown;

[0033] Figure 7 A three-dimensional schematic diagram of a flat-mouth sealing valve body is shown.

[0034] The above drawings include the following reference numerals:

[0035] 1. Vent valve body; 2. Flat-mouth sealing valve body; 3. Positioning ring; 4. Elastic retaining ring; 5. First vent plug protective cover; 6. Second vent plug protective cover; 7. Common brake cylinder body; 8. First piston; 9. First non-sealed cavity; 10. First sealed cavity; 11. Second non-sealed cavity; 12. Cylinder body with parking brake; 13. Second piston; 14. Second sealed cavity; 15. Filter hole; 16. Waterproof vent plug body; 17. Filter surface; 18. Opening; 19. Open; 20. Ventilation space; 21. Valve body cavity. DETAILED DESCRIPTION

[0036] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0037] The present invention is further described in detail below in conjunction with specific embodiments, and these embodiments cannot be understood as limiting the scope of protection claimed by the present invention. The term "including" when used indicates the existence of a feature, but does not exclude the existence or addition of one or more other features; the orientation or position relationship indicated by the terms "lateral", "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention; in addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance.

[0038] In the description, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. In addition, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0039] The invention adopts a normally closed sealing structure based on rubber elasticity, which solves the problem that water in the external atmosphere enters the non-sealed cavity of the brake cylinder through the waterproof vent plug.

[0040] like Figure 2 , Figure 4 As shown, the waterproof vent plug includes a vent valve body 1, a positioning ring 3, and a flat-mouth sealing valve body 2. The vent valve body 1 has a ventilation space 20 and a accommodating cavity inside. The accommodating cavity accommodates the positioning ring 3, and the positioning ring 3 has a hollow cavity. The flat-mouth sealing valve body 2 includes a wedge-shaped portion and a mounting portion. The mounting portion is installed between the vent valve body 1 and the positioning ring 3. The wedge-shaped portion includes two inclined surfaces, and an opening 18 is formed in the direction where the inclined surfaces intersect. The opening 18 is in a normally closed state, and an open opening 19 is formed on the side away from the direction where the inclined surfaces intersect, and the inclined surfaces enclose a valve body cavity 21. The valve body cavity 21 is connected to the vent space 20 to form an air plug cavity. As shown Figure 5 , 6 As shown, the waterproof vent plug is a one-way exhaust, and the gas can only be discharged into the atmosphere along the air plug cavity, so that water cannot enter the brake cylinder from the external atmosphere through the waterproof vent plug with the air, thereby preventing the water entering the brake cylinder from solidifying on the cylinder wall, seriously affecting the sealing of the brake cylinder sealing cavity, causing air leakage in the brake cylinder sealing cavity to connect the sealed cavity with the non-sealed cavity, affecting the brake function of the brake cylinder and failing to brake normally.

[0041] like Figure 2 , Figure 7 As shown, the wedge-shaped portion further includes two parallel horizontal planes, which are arranged at the ends where the inclined planes intersect and extend along the direction where the inclined planes intersect to form an extended closing portion of the opening 18 , thereby improving the sealing performance of the opening 18 .

[0042] The positioning ring 3 includes a mounting groove, and the mounting portion of the flat-mouth sealing valve body 2 includes an annular protrusion, which is accommodated in the mounting groove of the positioning ring 3, thereby improving the mounting accuracy. The positioning ring 3 also includes a filtering surface 17. The filtering surface 17 is arranged on the side opposite to the mounting groove, and is provided with a plurality of filtering holes 15, which can prevent large particles of sand and stone from getting stuck in the opening 18 of the flat-mouth sealing valve body 2, and prevent the opening 18 from becoming normally open due to blockage by sand and stone. The plurality of filtering holes 15 can be 4, 6, etc., which can be selected according to actual needs. The mounting portion of the flat-mouth sealing valve body 2 also includes an annular groove, which can accommodate a sealing ring to enhance the air tightness of the waterproof vent plug.

[0043] The waterproof vent plug also includes an elastic circlip 4, which is installed in the accommodating cavity of the vent valve body 1 and fits the filter surface 17 of the positioning ring 3. There are two mounting holes on the elastic circlip 4. When installing the elastic circlip, use needle-nosed pliers to clamp the mounting holes to reduce the diameter of the elastic circlip. After putting it into the groove, release the needle-nosed pliers. The diameter of the elastic circlip will recover to a diameter slightly smaller than the natural diameter under the action of its own elasticity and then get stuck in the groove, thereby fixing the positioning ring 3.

[0044] Among them, the components formed by the vent valve body 1, the flat-mouth sealing valve body 2, the positioning ring 3 and the elastic retaining ring 4 are the waterproof vent plug body 16.

[0045] In addition to the waterproof vent plug body 16, the waterproof vent plug also includes a first vent plug protective sleeve 5. The first vent plug protective sleeve 5 includes a first mounting portion and a first exhaust portion. The first mounting portion cooperates with the vent valve body 1. The axis of the first mounting portion is parallel to the axis of the first exhaust portion. The first vent plug protective sleeve 5 is sleeved on the vent valve body 1. The first exhaust portion extends the exhaust port of the waterproof vent plug, thereby reducing the probability of the flat-mouth sealing valve body 2 being covered by ice and snow under harsh working conditions, making the waterproof vent plug more difficult to be blocked, and also keeping water in the external atmosphere away from the flat-mouth sealing valve body 2. The first vent plug protective sleeve 5 and the positioning ring 3 constitute graded filtration.

[0046] The present invention also proposes a commonly used brake cylinder, such as Figure 1As shown, the above-mentioned waterproof vent plug is used in the brake cylinder. The commonly used brake cylinder body 7 includes a first piston 8. One side of the first piston 8 is a first sealed chamber 10, and the other side is a first non-sealed chamber 9. The first non-sealed chamber 9 is connected to the air plug chamber. When the brake cylinder is relieved, the first piston 8 is retracted and moves in a direction away from the first non-sealed chamber 9, so that the cavity space of the first non-sealed chamber 9 becomes larger, and the pressure of the first non-sealed chamber 9 is less than the external atmospheric pressure of the air plug chamber. At this time, the wedge-shaped structure of the flat-mouth sealing valve body 2 is compressed, and the flat-mouth sealing valve body 2 is tightly closed, and gas and water cannot enter the non-sealed chamber through the flat-mouth sealing valve body 2. When the brake cylinder brakes, the first piston 8 is pushed out and moves in a direction close to the first non-sealed chamber 9, so that the cavity space of the first non-sealed chamber 9 becomes smaller. At this time, the pressure of the first non-sealed chamber 9 is greater than the external atmospheric pressure of the air plug chamber, and the flat-mouth sealing valve body 2 is opened. At this time, the non-sealed cavity is connected to the external atmosphere, and the gas and liquid can be discharged from the non-sealed cavity during this period. When the pressure on both sides of the flat-mouth sealing valve body 2 is balanced, the opening 18 will be closed again to a normally closed state.

[0047] The waterproof vent plug of the present invention separates the non-sealed cavity from the external atmosphere by the flat-mouth sealing valve body 2 made of rubber material inside the waterproof vent plug, and the flat-mouth sealing valve body 2 is extremely well sealed with other parts of the waterproof vent plug, so that gas and liquid can only pass through the opening 18 of the flat-mouth sealing valve body 2.

[0048] For the embodiment applied to the parking brake cylinder, the waterproof vent plug waterproof vent plug body 16 also includes a second vent plug protective sleeve 6. The second vent plug protective sleeve 6 includes a second mounting portion and a second exhaust portion, the second mounting portion cooperates with the vent valve body 1, the axis of the second mounting portion and the axis of the second exhaust portion intersect, and the axis of the second exhaust portion is slightly tilted downward horizontally, which helps the water splashed therein to flow out under the action of gravity. The second vent plug protective sleeve 6 is sleeved on the vent valve body 1 to extend the exhaust port of the waterproof vent plug. The second vent plug protective sleeve 6 and the positioning ring 3 constitute a graded filter.

[0049] The parking brake cylinder provided by the present invention is as follows Figure 3 As shown, a second piston 13 is arranged in the cylinder body 12 with a parking brake cylinder, and one side of the second piston 13 is a second sealed chamber 14, and the other side is a second non-sealed chamber 11. The second non-sealed chamber 11 is connected to the air plug chamber. When the parking brake cylinder is released, the second piston 13 is retracted and moves away from the second non-sealed chamber 11, so that the cavity space of the second non-sealed chamber 11 becomes larger, so that the pressure of the second non-sealed chamber 11 is less than the external atmospheric pressure of the air plug chamber, and the flat-mouthed sealing valve body 2 is tightly closed. When the brake cylinder is braked, the second piston 13 is pushed out and moves toward the direction close to the second non-sealed chamber 11, so that the cavity space of the second non-sealed chamber 11 becomes smaller, and the pressure of the second non-sealed chamber 11 is greater than the external atmospheric pressure of the air plug chamber, and the flat-mouthed sealing valve body 2 is opened.

[0050] The waterproof vent plug of the present invention uses a flat-mouth sealing valve body 2. When the non-sealed cavity is inhaling air, the waterproof vent plug is closed to prevent air and water from entering the non-sealed cavity through the waterproof vent plug; when the non-sealed cavity is exhausted, the waterproof vent plug is opened to exhaust the air and water in the non-sealed cavity and balance the pressure of the non-sealed cavity and the external atmosphere.

[0051] In summary, from the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0052] 1. The present invention adopts a normally closed sealing structure based on rubber elasticity, which solves the problem that water in the external atmosphere enters the non-sealed cavity of the brake cylinder through the waterproof vent plug;

[0053] 2. The waterproof vent plug is a one-way exhaust, and the gas can only be discharged to the atmosphere along the air plug cavity, so that water cannot enter the brake cylinder from the outside atmosphere through the waterproof vent plug with air;

[0054] 3. The flat-mouth sealing valve body has an extended closing part, which improves the sealing performance of the opening;

[0055] 4. The positioning ring includes a filtering surface, which can prevent large particles of sand and stone from getting stuck in the opening of the flat-mouth sealing valve body, and prevent the opening from becoming normally open due to blockage by sand and stone. The positioning ring and the vent plug protective cover constitute graded filtration;

[0056] 5. The first vent plug protective cover and the second vent plug protective cover extend the exhaust port of the waterproof vent plug, thereby reducing the probability of the flat-mouth sealing valve body being covered by ice and snow under severe working conditions.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A waterproof vent plug, characterized in that: include: A vent valve body (1), wherein the vent valve body (1) has a vent space (20) and a receiving cavity inside; A positioning ring (3), the positioning ring (3) being installed in the accommodating cavity, the positioning ring (3) having a hollow cavity; A flat-mouth sealing valve body (2), the flat-mouth sealing valve body (2) comprising a wedge-shaped portion and a mounting portion, the mounting portion being mounted between the ventilation valve body (1) and the positioning ring (3); the wedge-shaped portion comprising two inclined surfaces, forming an opening (18) in the direction in which the inclined surfaces intersect, the opening (18) being in a normally closed state, and forming an open opening (19) on the side away from the direction in which the inclined surfaces intersect, the inclined surfaces enclosing a valve body cavity (21); the valve body cavity (21) is connected to the ventilation space (20) to form an air plug cavity.

2. The waterproof vent plug according to claim 1, characterized in that: The wedge-shaped portion further comprises two parallel horizontal surfaces, which are arranged at the ends where the inclined surfaces intersect and extend along the direction where the inclined surfaces intersect to form an extended closing portion of the opening (18).

3. The waterproof vent plug according to claim 2, characterized in that: The positioning ring (3) comprises a mounting groove, and the mounting portion of the flat-mouth sealing valve body (2) comprises an annular protrusion, and the annular protrusion is accommodated in the mounting groove of the positioning ring (3).

4. The waterproof vent plug according to claim 3, characterized in that: The mounting portion of the flat-mouth sealing valve body (2) further comprises an annular groove, and the annular groove can accommodate a sealing ring to enhance the air tightness of the waterproof vent plug.

5. The waterproof vent plug according to claim 4, characterized in that: The positioning ring (3) further comprises a filtering surface (17), wherein the filtering surface (17) is arranged on a side opposite to the mounting groove, and a plurality of filtering holes (15) are arranged on the filtering surface (17).

6. The waterproof vent plug according to claim 5, characterized in that: The waterproof vent plug also includes an elastic retaining ring (4), which is installed in the accommodating cavity of the vent valve body (1) and fits the filtering surface (17) of the positioning ring (3). The elastic retaining ring (4) fixes the positioning ring (3).

7. The waterproof vent plug according to any one of claims 1 to 6, characterized in that: The waterproof vent plug also includes a first vent plug protective sleeve (5), which includes a first mounting portion and a first exhaust portion, the first mounting portion cooperates with the vent valve body (1), the axis of the first mounting portion is parallel to the axis of the first exhaust portion, and the first exhaust portion extends the exhaust port of the waterproof vent plug.

8. The waterproof vent plug according to any one of claims 1 to 6, characterized in that: The waterproof vent plug also includes a second vent plug protective sleeve (6), and the second vent plug protective sleeve (6) also includes a second mounting portion and a second exhaust portion, the second mounting portion cooperates with the vent valve body (1), the axis of the second mounting portion and the axis of the second exhaust portion intersect, and the axis of the second exhaust portion is horizontally inclined downward, and the second exhaust portion extends the exhaust port of the waterproof vent plug.

9. A common brake cylinder, comprising a first piston (8), one side of the first piston (8) being a first sealed chamber (10) and the other side being a first non-sealed chamber (9), characterized in that: The brake cylinder adopts the waterproof vent plug described in claim 7, the first non-sealed cavity (9) is connected to the air plug cavity, the first piston (8) is retracted when the brake cylinder is released, and the first piston (8) moves in the direction away from the first non-sealed cavity (9), so that the cavity space of the first non-sealed cavity (9) becomes larger, the pressure of the first non-sealed cavity (9) is less than the external atmospheric pressure of the air plug cavity, and the flat-mouth sealing valve body (2) is tightly closed; the first piston (8) is pushed out when the brake cylinder is braked, and the first piston (8) moves in the direction close to the first non-sealed cavity (9), and the cavity space of the first non-sealed cavity (9) becomes smaller, so that the pressure of the first non-sealed cavity (9) is greater than the external atmospheric pressure of the air plug cavity, and the flat-mouth sealing valve body (2) is opened.

10. A parking brake cylinder, comprising a second piston (13), one side of the second piston (13) being a second sealed chamber (14) and the other side being a second non-sealed chamber (11), characterized in that: The brake cylinder adopts the waterproof vent plug according to claim 8, the second non-sealed cavity (11) is connected to the vent cavity, and the second piston (13) is retracted when the parking brake cylinder is released. The second piston (13) moves in a direction away from the second non-sealed chamber (11), and the cavity space of the second non-sealed chamber (11) becomes larger, so that the pressure of the second non-sealed chamber (11) is less than the external atmospheric pressure of the air plug chamber, and the flat-mouthed sealing valve body (2) is tightly closed; the second piston (13) is pushed out when the brake cylinder brakes, and the second piston (13) moves in a direction close to the second non-sealed chamber (11), and the cavity space of the second non-sealed chamber (11) becomes smaller, so that the pressure of the second non-sealed chamber (11) is greater than the external atmospheric pressure of the air plug chamber, and the flat-mouthed sealing valve body (2) is opened.

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