Air bleeding pipe joint   

1. Field of the Invention

The present invention relates to an air bleeding pipe joint connected to a circulation pipeline for an engine cooling water and adapted for bleeding an air in the circulation pipeline.

2. Description of Related Art

In a motor vehicle, when an engine cooling water is supplied in a circulation pipeline for the engine cooling water, an air is sometimes confined within the circulation pipeline, and as a result, it is hard to inject the engine cooling water in a radiator. As a countermeasure, an air bleeding portion has been conventionally provided at a part of the circulation pipeline.

For example, Patent document 1 as below discloses a technique of providing such air bleeding portion.

Further, Patent Document 2 as below also discloses such air bleeding portion provided in a circulation pipeline for an engine cooling water. According to the disclosure of Patent Document 2, an air bleeding pipe joint as the air bleeding portion comprises a pair of connection pipe portions inserted in and connected to the circulation pipeline, a branch pipe portion branched from the connection pipe portions and having an air bleeding hole in an inside thereof, and a plug body removably mounted to the branch pipe portion for opening and closing the air bleeding hole, and the air bleeding pipe joint is provided in a circulation route for the engine cooling water, namely at a part of the circulation pipeline for the engine cooling water for bleeding or discharging outwardly an air contained in the circulation pipeline by opening the air bleeding hole.

FIG. 8 shows a specific example of the air bleeding pipe joint as above.

In the Figure, reference numeral 200 indicates a heater hose (a part of a pipeline for introducing a cooling water heated by an engine to a heater core for heating a vehicle passenger compartment) constituting a part of a circulation pipeline for the engine cooling water, and reference numeral 202 indicates an air bleeding pipe joint connected to these heater hoses 200.

The air bleeding pipe joint 202 is formed in a T-shape as shown in FIG. 8B. The air bleeding pipe joint 202 has a pair of connection pipe portions 204 and a branch pipe portion 206 branched therefrom. The pair of the connection pipe portions 204 and the branch pipe portion 206 comprise a joint body 207. These connection pipe portions 204 are inserted in and connected to a pair of heater hoses 200, and then fixed by hose clamps 208 thereto, respectively.

The branch pipe portion 206 has an air bleeding hole 210 in an inside thereof, and the air bleeding pipe joint 202 is adapted for bleeding or discharging outwardly an air contained within the circulation pipeline through the air bleeding hole 210.

Reference numeral 212 indicates a plug or plug body for opening and closing the air bleeding hole 210. The plug 212 has an externally threaded portion 214, the externally threaded portion 214 is screwed into an internally threaded portion 216 in an inner surface of the branch pipe portion 206, and thereby the plug 212 is attached to the branch pipe portion 206.

The plug 212 has a large diameter head portion 217 of hexagonal shape, and the head portion 217 protrudes upwardly along an axis of the branch pipe portion 206 and perpendicular to the axis thereof with respect to the branch pipe portion 206.

FIG. 9 is an enlarged view showing a plug 212 that is attached to a branch pipe portion 206, along with its vicinity portion (an air bleeding pipe joint shown in FIG. 9 is different from that shown in FIG. 8).

As shown in the Figure (FIG. 9), the plug 212 has a male fitting surface 220 of a circular cross-section that is defined by an outer peripheral surface of a lower portion of a shaft portion 218. The male fitting surface 220 includes an annular retaining groove in which an elastic O-ring (annular sealing member) 222 is retained. Thus configured male fitting surface 220 fits with or in a corresponding female fitting surface 224 of the branch pipe portion 206. An air-tight seal is provided by the O-ring 222 between the male fitting surface 220 and the female fitting surface 224.

Reference numeral 226 indicates a seating surface defined by a lower surface of a head portion 217 of the plug 212. The plug 212 is screwed in the branch pipe portion 206 downwardly in the Figure to such position that the seating surface 226 seats on a corresponding upwardly facing seated surface 228 of the branch pipe portion 206 in a tight-fit condition, and thereby is mounted to the branch pipe portion 206.

By the way, for inspecting whether the O-ring 222 is correctly attached in the air bleeding pipe joint 202, an air-tightness test is conducted. In the air-tightness test, an air bleeding hole 210 is closed by screwing the plug 217 in the branch pipe portion 206.

However, when the plug 212 is tightly screwed in the branch pipe portion 206, an externally threaded portion 214 of the plug 212 happens to tightly contact with an internally threaded portion 216 of the branch pipe portion 206, or the seating surface 226 of the head portion 217 of the plug 212 happens to tightly contact with the seated surface 228 of the branch pipe portion 206. In this state, a seal is formed in a tight contact region, namely between the externally threaded portion 214 and the internally threaded portion 216, or between the seating surface 226 and the seated surface 228, an air is not allowed to be bled outwardly through the tight contact region. Therefore, even if the O-ring 222 fails to be attached in the air bleeding pipe joint 212, in the air-tightness test, the air bleeding pipe joint 212 happens to meet the test for acceptable air-tightness.

In order to prevent such inconvenience, the air-tightness test is conducted for the air bleeding pipe joint 202 with the plug 212 being not fully screwed in the branch pipe portion 206 (in incompletely screwed condition), and after the test, the plug 212 is completely screwed to the branch pipe portion 206. However, in this case, if the plug 212 fails to be finally screwed in the branch pipe portion 206 after the test, the air bleeding pipe joint 202 is accidentally assembled to a pipeline of a motor vehicle with the plug 212 being incompletely screwed in the branch pipe portion 206.

So, in this test method, there is a need for additional step separately for preventing such inconvenience.

However, such additional step could be a complicating factor in an assembly of an air bleeding pipe joint or an inspecting procedure of the air bleeding pipe joint.

[Patent Document 1] JP-A-61-93225

[Patent Document 2] JP-A-2004-161163

Under the foregoing circumstances, it is an object of the present invention to provide an air bleeding pipe joint that allows an operator to detect a failure of attachment of an O-ring, even if a plug is completely screwed in a branch pipe portion. In such air bleeding pipe joint, there is no fear that the air bleeding pipe joint is assembled to a pipeline of a motor vehicle without an O-ring.

According to the present invention, there is provided a novel air bleeding pipe joint. The air bleeding pipe joint comprises (a) a pair of connection pipe portions inserted in and connected to a circulation pipeline for an engine cooling water, (b) a branch pipe portion branched from the connection pipe portions in upstanding condition or upwardly standing condition and having an air bleeding hole in an inside thereof, and (c) a plug or plug body removably mounted to the branch pipe portion for opening and closing the air bleeding hole. The air bleeding hole includes an internally threaded portion and a female fitting surface under the internally threaded portion. The plug body has a head portion or a large diameter head portion of an upper end portion thereof with an under surface defining a seating surface, an externally threaded portion, and a male fitting surface under the externally threaded portion. The air bleeding pipe joint further comprises (d) an elastic annular sealing member providing an air-tight seal between the female fitting surface of the branch pipe portion and the male fitting surface of the plug body mounted to the branch pipe portion. The plug body is mounted to the branch pipe portion with the externally threaded portion in threaded engagement with the internally threaded portion such that the seating surface of the head portion seats on a corresponding upwardly facing seated surface of the branch pipe portion. An air discharge path is provided on an upper end of the branch pipe portion and/or the plug body with respect to a sealing at which the sealing member is disposed or a section to be sealed by the sealing member. The air discharge path discharges outwardly an air that leaks upwardly through the sealing position or the section. The plug body is allowed for repeated removal from and reattachment to the branch pipe portion.

According to one aspect of the present invention, the plug body has an overlapping surface that overlaps with an overlapped surface of the branch pipe portion, the overlapping surface and/or the overlapped surface is provided with a recessed portion that allows an air to pass therethrough and defines at least a part of the air discharge path. For example, the seating surface of the overlapping surface of the plug body and/or the seated surface of the overlapped surface of the branch pipe portion is provided with the recessed portion.

According to one aspect of the present invention, the plug body has an overlapping surface that overlaps with an overlapped surface of the branch pipe portion, one of the overlapping surface and the overlapped surface is provided with a protruding portion protruding toward the other of the overlapping surface and the overlapped surface for creating a gap between the overlapping surface and the overlapped surface, and the gap defines at least a part of the air discharge path. For example, one of the seating surface of the overlapping surface of the plug body and the seated surface of the overlapped surface of the branch pipe portion is provided with the protruding portion.

According to one aspect of the present invention, the plug body has an overlapping surface that overlaps with an overlapped surface of the branch pipe portion, the overlapping surface and/or the overlapped surface is formed into a roughened surface having irregularities or protuberances, and the gap in the roughened surface defines at least a part of the air discharge path. For example, the seating surface of the overlapping surface of the plug body and/or the seated surface of the overlapped surface of the branch pipe portion is formed into the roughened surface having the irregularities or the protuberance.

According to one aspect of the present invention, a recessed path or a through-bore path is provided in an upper end of the branch pipe portion and/or the plug body with respect to the sealing position, the recessed path or the through-bore path extends continuously from the sealing position and has an extremity end open to outside, and the recessed path or the through-bore path serves as the air discharge path. The recessed path or the through-bore path extends from the sealing position to the extremity end.

According to one aspect of the present invention, the plug body, a joint body comprising the pair of the connection pipe portions and the branch pipe portion are molded resin products.

According to the present invention, in an air bleeding pipe joint comprising (a) a pair of connection pipe portions inserted in and connected to a circulation pipeline for an engine cooling water, (b) a branch pipe portion branched from the connection pipe portions in upstanding condition and having an air bleeding hole in an inside thereof, (c) a plug body for opening and closing the air bleeding hole which has a head portion of an upper end portion thereof with an under surface defining a seating surface and is removably mounted to the branch pipe portion in threaded engagement therewith such that the seating surface of the head portion seats on a corresponding upwardly facing seated surface of the branch pipe portion, and (d) an elastic annular sealing member providing an air-tight seal between the plug body and the air bleeding hole, an air discharge path is provided between the seating surface and the seated surface.

According to the present invention, in an air bleeding pipe joint comprising (a) a pair of connection pipe portions inserted in and connected to a circulation pipeline for an engine cooling water, (b) a branch pipe portion branched from the connection pipe portions in upstanding condition and having an air bleeding hole in an inside thereof, (c) a plug body for opening and closing the air bleeding hole which has a head portion of an upper end portion thereof with an under surface defining a seating surface and is removably mounted to the branch pipe portion in threaded engagement therewith such that the seating surface of the head portion seats on a corresponding upwardly facing seated surface of the branch pipe portion, and (d) an elastic annular sealing member providing an air-tight seal between the plug body and the air bleeding hole, an air discharge path extends continuously from a sealing position at which the sealing member is disposed or a section to be sealed by the sealing member and has an extremity end open to outside.

As stated above, according to the present invention, an air discharge path is provided on an upper end with respect to a sealing position at which a sealing member is disposed or the section to be sealed by the sealing member, for discharging outwardly an air that leaks upwardly through the sealing position or the section. Therefore, when an air-tightness test is conducted for an air bleeding pipe joint in which the sealing member fails to be attached, an air can be positively discharged outwardly through the air discharge path.

On the other hand, when the air-tightness test is conducted for the air bleeding pipe joint in which the sealing member is correctly attached, an air is not discharged or leaked outwardly since an air-tight seal is positively provided at the sealing position of the sealing member or the section to be sealed by the sealing member.

Thus, according to the present invention, it can be positively detected whether the sealing member is attached in the air bleeding pipe joint, by conducting the air-tightness test.

As described above, in the past, in order to verify attachment of a sealing member, an air-tightness test is conducted for an air bleeding pipe joint with a plug body being not fully screwed in a branch pipe portion. So, there is a need for adding a step of screwing the plug body completely in the branch pipe portion after the air-tightness test in an assembling procedure or an inspection procedure of the air bleeding pipe joint. According to the present invention, the need for this bothersome step can be eliminated.

In the present invention, the plug body may have an overlapping surface that overlaps with an overlapped surface of the branch pipe portion. One of the overlapping surface and the overlapped surface may be provided with a recessed portion for allowing an air to pass therethrough, and the recessed portion may define at least a part of the air discharge path.

Or, the other of the overlapping surface and the overlapped surface may be also provided with the recessed portion for allowing an air to pass therethrough.

In the present invention, one of the overlapping surface and the overlapped surface may be provided with a protruding portion protruding toward the other of the overlapping surface and the overlapped surface for creating a gap between the overlapping surface and the overlapped surface, and the gap may define at least a part of the air discharge path.

In this case, the other of the overlapping surface and the overlapped surface may be also provided with a protruding portion protruding toward the one of the overlapping surface and the overlapped surface.

In the present invention, the overlapping surface and/or the overlapped surface may be formed into a roughened surface having irregularities or protuberances, and a gap in the roughened surface may define at least a part of the air discharge path.

Here, the roughened surface means a surface having a roughness of 50 μm to 500 μm in terms of Rz specified in JIS B0601.

As stated above, in a conventional air bleeding pipe joint, when the plug body is tightly screwed in the branch pipe portion, there is a fear that the seating surface of the plug body tightly contacts with the seated surface of the branch pipe portion, a seal is formed between the seating surface and the seated surface, and an air that leaks through the sealing position is confined internally.

However, when the recessed portion is provided in the seating surface of the overlapping surface and/or the seated surface of the overlapped surface for allowing an air to pass through the recessed portion, it can be prevented that the air bleeding pipe joint without the sealing member happens to meet the test for acceptable air-tightness since an air that leaks through the sealing position is confined internally.

When the above protruding portion is provided on the seating surface of the overlapping surface and/or the seated surface of the overlapped surface, this protruding portion can produce the same effect as the recessed portion stated above.

Or, the seating surface and/or the seated surface may be formed into the roughened surface having the irregularities or the protuberances. This configuration also can produce the same effect as the recessed portion stated above.

Here, the roughened surface means a surface having a roughness of 50 μm to 500 μm in terms of Rz specified in JIS B0601.

Or, a recessed path or a through-bore path may be provided in the upper end with respect to the sealing position or the section to be sealed. The recessed path or the through-bore path extends continuously from the sealing position or the section to be sealed and has an extremity end open to outside. The recessed path or the through-bore path may serve as the air discharge path. In this configuration, even if a seal is formed between the overlapping surface of the plug body and the overlapped surface of the branch pipe portion, an air that leaks through the sealing position or the section to be sealed can be positively discharged outwardly through the air discharge path defined by the recessed path or the through-bore path.

The present invention produces a great effect in particular in the case that the plug body, a joint body comprising a pair of the connection pipe portions and the branch pipe portion are molded resin products.

The reason is that in the air bleeding pipe joint of the molded resin product, the overlapping surface of the plug body tends to tightly contact with the overlapped surface of the branch pipe portion and an air-tight seal is easily formed between the overlapping surface and the overlapped surface, resulting that a air is easily confined internally by a tightly contact region therebetween.

Now, a description will be given in detail of an embodiment in accordance with the present invention on the basis of the accompanying drawings.

FIG. 1 is an explanatory view showing a position at which an air bleeding pipe joint according to one embodiment of the present invention is applied.

FIG. 2A is a perspective exploded view of the air bleeding pipe joint of FIG. 1.

FIG. 2B is a perspective view of the air bleeding pipe joint of FIG. 1 which is assembled.

FIG. 3A is an exploded, side-sectional view of the air bleeding pipe joint of FIG. 1.

FIG. 3B is a side-sectional view of the air bleeding pipe joint of FIG. 1 which is assembled.

FIG. 4A is a perspective view showing that a protrusion is provided on a seated surface of a branch pipe portion.

FIG. 4B is a perspective view showing that another protrusion is provided on the seated surface of the branch pipe portion.

FIG. 4C is a perspective view showing that yet another protrusion is provided on the seated surface of the branch pipe portion.

FIG. 4D is a perspective view showing that a recessed portion is provided on the seated surface of the branch pipe portion.

FIG. 4E is a perspective view showing that another recessed portion is provided on the seated surface of the branch pipe portion.

FIG. 5A is a perspective view showing that a seating surface of a plug body is formed into a roughened surface.

FIG. 5B is a perspective view showing that the seating surface of the plug body and the seated surface of the branch pipe portion are formed into the roughened surfaces.

FIG. 6A is a perspective view showing that the protrusion is provided on the seating surface of the plug body.

FIG. 6B is a perspective view showing that the another protrusion is provided on the seating surface of the plug body.

FIG. 6C is a perspective view showing that the yet another protrusion is provided on the seating surface of the plug body.

FIG. 6D is a perspective view showing that the recessed portion is provided on the seating surface of the plug body.

FIG. 6E is a perspective view showing that the another recessed portion is provided on the seating surface of the plug body.

FIG. 7 is a sectional view showing that a through-bore path is formed in a plug body.

FIGS. 8A to 8C are views showing a conventional air bleeding pipe joint.

FIG. 9 is a view showing a relevant part of another conventional air bleeding pipe joint.

With reference to FIG. 1, reference numeral 10 indicates a circulation pipeline for an engine cooling water, reference numeral 10-1 indicates a radiator-end pipeline communicating between an engine 12 and a radiator 14, and reference numeral 10-2 indicates a heater-end pipeline communicating between the engine 12 and a heater core 16 for heating a vehicle compartment.

In the Figure, reference numeral 18-1 indicates a upper radiator hose made of rubber, constituting a part of the circulation pipeline 10, specifically a part of the radiator-end pipeline 10-1, and reference numeral 18-2 indicates a lower radiator hose.

Reference numeral 20-1 indicates an upper heater hose made of rubber, constituting similarly a part of the circulation pipeline 10, specifically a part of the heater-end pipeline 10-2, and reference numeral 20-2 indicates a lower heater hose.

Further, reference numeral 22 indicates a water pump, and reference numeral 23 indicates a thermo valve with a thermostat function.

As seen in FIG. 1, an air bleeding pipe joint 24 of the present embodiment is connected between the upper heater hoses (hereinafter, simply referred to as heater hoses) 20-1, 20-1.

FIGS. 2 and 3 show a specific arrangement of the air bleeding pipe joint 24.

The air bleeding pipe joint 24 is made of resin, and has a T-shape as a whole. The air bleeding pipe joint 24 has a pair of connection pipe portions 26, and a branch pipe portion 28 uprising or upstanding from the connection pipe portions 26, perpendicular to the connection pipe portions 26. The connecting pipe portions 26 made of resin and the branch pipe portion 28 made of resin comprise a resin joint body.

Each of the pair of the connection pipe portions 26 is inserted in and connected to the heater hose 20-1. The connection pipe portion 26 is provided with an annular projecting portion that defines a bulge portion 30 on an outer peripheral surface of an extremity portion thereof.

The branch pipe portion 28 has an air bleeding hole 32 in an inside thereof. An air contained in the circulation pipeline 10 is discharged or bled outwardly through the air bleeding hole 32.

The branch pipe portion 28 has a female fitting surface 34 of circular cross-section defined by a lower portion of an inner surface thereof, and an internally threaded portion or female threaded portion 36 above the female fitting surface 34.

An upper end surface of the branch pipe portion 28 serves as an upwardly facing seated surface 38 on which a seating surface 48 of a plug 40 (to be described later) seats.

Reference numeral 40 indicates a plug or a plug body made of resin for closing or opening the air bleeding hole 32. The plug 40 is removably and threadably mounted to the branch pipe portion 28. The plug 40 has a shaft portion 42 of circular cross-section, and a head portion 44 of a disc shape on an upper end portion of the shaft portion 42. The head portion 44 has a diameter larger than the shaft portion 42.

The head portion 44 here has ribs 46 that are circumferentially spaced apart at a uniform pitch on an outer peripheral surface of the head portion 44 throughout an entire circumference of the head portion 44.

In the present embodiment, the head portion 44 also serves as a knob for rotating operation of the plug body 40. The above ribs 46 serve a slip-resistant function during rotating operation of the head portion 44.

Meanwhile, an engaging recessed portion 47 is formed at a center in an upper surface of the head portion 44. The engaging recessed portion 47 has a hexagonal planar shape. The head portion 44 can be rotated by a tool such as a hexagonal wrench that is adapted to fit and engage in the engaging recessed portion 47.

An under surface of the head portion 44 defines a flat seating surface 48. The seating surface 48 seats on a seated surface 38 that is defined by an upper end surface or top surface of the above branch pipe portion 28.

Here, the seating surface 48 and the seated surface 38 serve as or define overlapping surfaces that overlap each other in a vertical direction, an up-and-down direction or an axial direction of the branch pipe portion 28. Or, the seating surface 48 serves as or defines an overlapping surface, and the seated surface 38 serves as or defines an overlapped surface.

An outer peripheral surface of a lower portion of the shaft portion 42 of the plug 40 is formed into a male fitting surface 49 of circular cross-section. An annular O-ring groove 50 is formed in the male fitting surface 49, and an elastic O-ring 52 of circular ring shape is retained in the annular O-ring groove 50.

And, the shaft portion 42 has an externally threaded portion or male threaded portion 54 that is defined by an outer peripheral surface thereof, above the O-ring or sealing member 52.

Here, the externally threaded portion 54 and the internally threaded portion 36 may serve as or define overlapping surfaces that overlap each other, or the externally threaded portion 54 may serve as or define an overlapping surface, and the internally threaded portion 36 may serve as or define an overlapped surface.

When the externally threaded portion 54 of the plug or plug body 40 is screwed and tightened downwardly in the internally threaded portion 36 of the branch pipe portion 28, the male fitting surface 49 of the shaft portion 42 fits with the female fitting surface 34 of the branch pipe portion 28 via the O-ring 52, and an air-tight seal is formed between the male fitting surface 49 and the female fitting surface 34 by the O-ring 52 as shown in FIG. 3B.

And, at that time, the seating surface 48 defined by the under surface of the head portion 44 seats on the seated surface 38 defined by the upper end surface of the branch pipe portion 28.

In the present embodiment, the seated surface 38 of the branch pipe portion 28 is formed entirely into a roughened surface 38a having fine irregularities or fine protuberances.

Here, the roughened surface 38a has a roughness or roughness degree of 50 μm in terms of Rz (JIS B0601). This also applies to roughened surfaces 36a, 39a, 54a to be described later.

As a result, in the present embodiment, as shown in FIG. 3B, even when the plug 40 is fully screwed and tightened with respect to the branch pipe portion 28, tight contact between the seating surface 48 defined by the under surface of the head portion 44 of the plug 40 and the seated surface 38 of the branch pipe portion 28 is prevented by the roughened surface 38a. A gap is created between the seating surface 48 and the seated surface 38 by the fine irregularities of the roughened surface 38a.

In case that the O-ring 52 fails to be attached in the O-ring groove 50, namely at a sealing position, an air leaks from the sealing position. In this case, the gap serves as an air discharge path for discharging or exhausting to the outside the air that leaks through the sealing position.

In a conventional air bleeding pipe joint, when a plug is fully screwed and strongly tightened, a seating surface of a large diameter head portion tightly and closely contacts with a seated surface of a branch pipe portion. This close contact relation therebetween sometimes does not allow an air leaking through the sealing position to be bled to the outside, and confines the air internally. However, according to the present embodiment, close contact between the seating surface 48 and the seated surface 38 is prevented and an air discharge path is formed therebetween. Therefore, in an air-tightness inspection for the air bleeding pipe joint 24, when no air leaks, the O-ring 52 is positively attached correctly, and when an air leaks, the O-ring 52 positively fails to be attached. So, it can be positively detected and determined whether the O-ring 52 is attached correctly.

Next, FIG. 4A shows another embodiment of the present invention. In the embodiment of FIG. 4A, protrusions 56 are provided at a plurality of positions spaced circumferentially, on the seated surface 38 (the seated surface 38 in FIG. 2A without any fine irregularities) of the branch pipe portion 28. Each of the protrusions 56 protrudes upwardly, toward the seating surface 48 of the plug or plug body 40.

Here, each of the protrusions 56 has a conical shape, and the protrusions 56 are arranged at four positions circumferentially spaced by 90°.

However, the number of the protrusion 56 may be varied and the shape of the protrusion 56 may be varied.

FIG. 4B shows a protrusion 58 that has a shape different from the protrusion 56 of FIG. 4A. The protrusion 58 as shown in FIG. 4B has a square cross-section, and extends radially, through an entire width of the seated surface 38 (the seated surface 38 in FIG. 2A without any fine irregularities) so as to cross the seated surface 38.

FIG. 4C shows further another protrusion 59 that has a triangle cross-section, and extends radially, through the entire width of the seated surface 38 (the seated surface 38 in FIG. 2A without any fine irregularities) so as to cross the seated surface 38.

In the protrusion 56, 58, 59 as shown in FIGS. 4A, 4B and 4C, a protruding height of the protrusion 56, 58, 59 is 0.3 mm to 1.0 mm here. However, the protruding height may be changed properly.

As stated, by providing the protrusion 56, 58, 59 on the seated surface 38, the gap is created between the seating surface 48 of the plug 40 and the seated surface 38 of the branch pipe portion 28 even when the plug 40 is fully screwed and tightened in the branch pipe portion 28, and the gap serves as an air discharge path for discharging outwardly an air that leaks through the sealing position.

So, also in this case, in an air-tightness inspection for the air bleeding pipe joint 24, an air positively leaks when the O-ring 52 fails to be attached, thereby it can be positively detected that the O-ring 52 fails to be attached.

On the other hand, FIGS. 4D and 4E show cases where the seated surface 38 (the seated surface 38 in FIG. 2A without any fine irregularities) is provided with a recess (recessed portion) 60, 61 instead of the protrusion 58, 59. The recess 60, 61 extends radially throughout an entire width of the seated surface 38 so as to cross the seated surface 38.

The recess 60 shown in FIG. 4D has a triangle cross-section, while the recess 61 shown in FIG. 4E has a square cross-section. Needless to say, the recess 60, 61 may have various cross-sectional shapes.

In the examples or embodiments shown in FIGS. 4D and 4E, the recess 60, 61 serves as an air discharge path for discharging outwardly an air leaking through the sealing position. Therefore, also in this case, in an air-tightness test, when the O-ring 52 fails to be attached, an air that leaks through the sealing position is bled positively outwardly.

So, it can be surely verified whether the O-ring 52 is attached by conducting the air-tightness test.

In the above embodiments, the seated surface 38 of the branch pipe portion 28 is formed into the roughened surface 38a, or the seated surface 38 of the branch pipe portion 28 is formed with the protrusion 56, 58, 59, or the recess 60, 61. On the other hand, the seating surface 48 defined by the under surface of the head portion 44 of the plug 40 may be formed into the roughened surface or may be formed with the protrusion 56, 58, 59, or the recess 60, 61.

FIG. 5 shows the case that the seating surface 48 is formed into a roughened surface 39a (FIG. 5A) and the case that the seated surface 38 and the seating surface 48 are formed into roughened surfaces 38a, 39a (FIG. 5B) as an example. The roughened surface 39a may have the same irregularities or protuberances as the roughened surface 38a.

Needless to say, the protrusion 56, 58, 59 or the recess 60, 61 as stated above may be formed on or in the seating surface 48 (refer to FIGS. 6A to 6E).

When an air is allowed to pass through between the externally threaded portion 54 and the internally threaded portion 36 in the air bleeding pipe joint 24, the externally threaded portion 54 and the internally threaded portion 36 are not necessarily required to be formed into the roughened surfaces. However, in a conventional air bleeding pipe joint, when a plug is fully screwed and tightened, an externally threaded portion of the plug may closely contact with an internally threaded portion of a branch pipe portion to form a seal therebetween, an air that leaks through the sealing position (an annular sealing groove) may be confined internally, and may be prevented from being bled outwardly. So, in this case, the air discharge path may be secured between the threaded portions by forming one or both of the externally threaded portion 54 and the internally threaded portion 36 into the roughened surface or roughened surfaces (54a, 36a) in the same form as the roughened surface 38a. In FIG. 5B and FIG. 6, the externally threaded portion 54 and the internal threaded portion 36 are formed into the roughened surfaces 54a, 36a, and define a part of an air discharge path (in FIGS. 6B to 6E, the branch pipe portion 28 of FIG. 6A is omitted).

Or, an air discharge path may be secured also by forming the recess 60, 61, etc. as stated above at least in one of the externally threaded portion 54 and the internally threaded portion 36.

FIG. 7 shows yet another embodiment according to the present invention.

In this embodiment, a through-bore path 62 with its extremity open to the outside is provided in a portion of the plug 40 above the sealing position. The through-bore path 62 extends continuously from the sealing position or a sealing section to be sealed by the O-ring 52, specifically from the O-ring groove 50. In this arrangement, even when an air is prevented from being bled by close contact between the seating surface 48 and the seated surface 38, by close contact between the externally threaded portion 54 and the internally threaded portion 36, or by close contact between the seating surface 48 and the seated surface 38 and tight contact between the externally threaded portion 54 and the internally threaded portion 36, an advantage may be obtained that an air leaking through the sealing position can be positively bled outwardly.

Here, the through-bore path 62 comprises a bore formed in the plug 40 and a recess between the seating surface 48 and the seated surface 38 or in the seating surface 48. The bore extends from the O-ring groove 50 upwardly in a vertical direction, and the recess extends in a radial direction.

However, the through-bore path 62 may take various other routes and different shapes. As the case may be, such through-bore path 62 may take a form of a through-bore extending through the shaft portion 42 of the plug 40 and the head portion 44, or extending through the branch pipe portion 28.

Although the preferred embodiment has been described, this is one of examples of the present invention. The present invention may be constructed and embodied in various configurations and modes within the scope of the present invention.