Pipe connecting device

Abstract

The utility model discloses a pipe connecting device which is used for being connected with an external pipe for conveying fluid and communicated with a fluid conveying pipeline. The pipe connecting device comprises a connecting body and a plurality of fastening nuts. Wherein the connecting body is provided with at least two connecting pipes, a bulging part is arranged on each connecting pipe, and the connecting pipes (or the connecting body) are connected with an external pipe by pressing the bulging parts into the external pipe; each connecting pipe is also provided with an external thread which is used for being in threaded connection with a fastening nut; the fastening nut is arranged on the external pipe in a penetrating and sleeving mode, a clamping part is arranged in the fastening nut, and when the external pipe is connected with the connecting pipe and the fastening nut and the connecting pipe are screwed tightly, the fastening nut clamps, pushes and presses the connecting position of the connecting pipe and the external pipe through the clamping part, so that the connecting pipe and the external pipe are fixedly connected, and double sealing is formed at the connecting position. And the sealing stability is improved. The pipe connecting device is simple in structure, low in production cost, convenient to use and good in application prospect.

Description

TECHNICAL FIELD

[0001] The utility model belongs to resin pipe connecting technical field, concretely relates to a pipe connecting device applied to the technical field manufacturing procedure of semiconductor, liquid crystal display panel, photovoltaic, biotechnology, pharmacy, medical equipment, microelectronic, optics, disk, automobile industry and aviation and aerospace field etc. BACKGROUND

[0002] In the manufacturing procedure of semiconductor, liquid crystal display panel, photovoltaic, biotechnology, pharmacy, medical equipment, microelectronic, optics, disk, automobile industry and aviation and aerospace field etc., the fluid used is some corrosive chemical liquid, gas or some fluid with super high purity requirement, and such fluid is usually transported by resin conduit in machine equipment, and the corrosion resistance of resin conduit can resist the erosion of chemical fluid, and the chemical inertness and the performance of not being easy to react with chemicals can also meet the requirements of super high purity and stability of transported fluid.

[0003] In actual production, these resin conduits need pipe connecting device to be connected between each other and between the resin conduit and equipment, and such pipe connecting device is usually prepared by resin material of the same type as the resin conduit, so that the commonly used resin material includes polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-ethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), polytrifluorochloroethylene (PCTFE), polyether ether ketone (PEEK), bisphenol A polysulfone (PSU), polyphenylene sulfone (PPSU) and polyether sulfone (PESU, PES) etc.

[0004] If the pipe connecting device used in production has poor or substandard connecting performance, leakage phenomenon may easily occur at the connecting position, and even safety accidents may be caused, so pipe connecting device with excellent and stable connecting and sealing effect is needed to ensure the safety of resin conduit connection. UTILITY MODEL CONTENTS

[0005] In order to improve the connecting performance of fluid conveying pipeline connection, the utility model provides a pipe connecting device for connecting external pipe conveying fluid.

[0006] The connecting body has at least two connecting pipes; each connecting pipe is provided with a bulging part and an external thread; the bulging part is located at the second end of the connecting pipe, and is used to be pressed into an external pipe to make the external pipe in an expanded state, so that the connecting pipe and the external pipe are connected; the external thread is arranged on the outer wall of the connecting pipe, and is used to be screwed with a fastening nut; and the external thread is located at the first side of the bulging part.

[0007] The fastening nut has an internal thread and a clamping part, and the internal thread and the clamping part are located inside the fastening nut; the internal thread is arranged on the inner wall of the first end of the fastening nut, and is used to be screwed with the external thread on the connecting pipe; and the clamping part is a circular ring structure arranged on the inner wall of the fastening nut, and is used to clamp and push the bulging part pressed into the external pipe; and the clamping part is located at the second side of the internal thread.

[0008] Each component has a first end or a first side close to one end or one side of the connecting body in the assembled state, and a second end or a second side away from one end or one side of the connecting body.

[0009] Optionally, the bulging part is formed by bulging outward from the outer wall of the connecting pipe;

[0010] The inner diameter of each connecting pipe is consistent with the inner diameter of the external pipe connected thereto.

[0011] Optionally, the bulging part has a first pressure receiving surface, a second pressure receiving surface and a third pressure receiving surface; wherein,

[0012] The first pressure receiving surface is located at the first side of the bulging part, the second pressure receiving surface is located at the second side of the bulging part, and the third pressure receiving surface is located between the first pressure receiving surface and the second pressure receiving surface.

[0013] The first pressure receiving surface and the second pressure receiving surface are conical curved surfaces; in the direction of the connecting pipe pointing to the second end thereof, the outer diameter of the first pressure receiving surface gradually increases, and the outer diameter of the second pressure receiving surface gradually decreases.

[0014] The third pressure receiving surface is a cylindrical curved surface; in the direction of the connecting pipe, the outer diameter of the third pressure receiving surface is constant.

[0015] Optionally, the outer diameter of the third pressure receiving surface is the maximum outer diameter of the bulging part, and the bulging part can form a seal with the external pipe at the third pressure receiving surface.

[0016] The fastening nut clamps and pushes the bulging part pressed into the external pipe at the second pressure receiving surface through the clamping part thereof, so that the bulging part also forms a seal with the external pipe at the second pressure receiving surface.

[0017] Optionally, the maximum outer diameter of the bulging part is smaller than the outer diameter of the external thread.

[0018] The end surface of the bulging part is a conical curved surface; the inner diameter of the port has an expanding trend in the direction along the connecting pipe and pointing to the second end thereof.

[0019] Optionally, the inner diameter of the clamping part is not less than the outer diameter of the outer pipe, so that the outer pipe can pass through the clamping part and the fastening nut can be sleeved on the outer pipe;

[0020] The inner diameter of the clamping part is less than the composite outer diameter, so that the clamping part can clamp and push the bulging part pressed into the outer pipe; the composite outer diameter is the outer diameter of the largest part of the bulging part pressed into the outer pipe.

[0021] Optionally, the pipe connecting device has a positioning structure for indicating the moderate fastening position of the fastening nut and the connecting pipe;

[0022] When the fastening nut and the connecting pipe are in the moderate fastening position, the clamping part is just clamped on the second pressure receiving surface of the bulging part, clamps and pushes the bulging part pressed into the outer pipe, and forms a seal between the bulging part and the outer pipe at the second pressure receiving surface.

[0023] Optionally, the positioning structure comprises an annular groove arranged on the inner wall of the nut body and a continuous or discontinuous annular protrusion arranged on the outer wall of the connecting pipe;

[0024] The annular groove is located on the first side of the internal thread;

[0025] The annular protrusion is located on the first side of the external thread;

[0026] When the fastening nut and the connecting pipe are in the moderate fastening position, the annular protrusion is just located in the annular groove.

[0027] Optionally, the shape and size of the annular protrusion match those of the annular groove;

[0028] The annular groove and the annular protrusion have a circular arc-shaped annular cross section.

[0029] Optionally, the connecting body further has a cavity, and each connecting pipe is in communication with the cavity;

[0030] A valve body is arranged in the cavity, and the valve body is used to control the communication or disconnection of each connecting pipe with the cavity;

[0031] The connecting body is a two-way or multi-way pipe connecting structure.

[0032] Compared with the prior art, the pipe connecting device provided by the utility model has the following advantages or beneficial effects:

[0033] (1) The bulging part of the utility model is pressed into the outer pipe and forms effective seal with the outer pipe at the second and third pressure-bearing surfaces, so that the connection between the connecting pipe and the outer pipe forms double seal, which guarantees the stability of the seal;

[0034] (2) The utility model sets the external thread on the outer wall of the connecting pipe to be screwed with the fastening nut, without setting other elements to cooperate with the fastening nut, which simplifies the structure of the device, reduces the manufacturing difficulty and cost, and has obvious economic benefits;

[0035] (3) The pipe connecting device of the utility model further has a positioning structure, which can not only indicate the moderate fastening position of the fastening nut and the connecting pipe, but also prevent the fastening nut from loosening. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 It is the assembly schematic view of the pipe connecting device in the embodiment one;

[0037] Figure 2 It is the disassembly schematic view of the pipe connecting device in the embodiment one;

[0038] Figure 3 It is the sectional view of the pipe connecting device in the embodiment one;

[0039] Figure 4 It is the schematic view of the connecting body in the embodiment one;

[0040] Figure 5 And Figure 6 It is the sectional view of the fastening nut in the embodiment one;

[0041] Figure 7 It is the schematic view of the connecting body in the embodiment two. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the embodiment clearer, the technical scheme of the embodiment will be described clearly and completely in combination with the drawings in the embodiment. Obviously, the described embodiment is a part of the embodiments of the utility model, rather than all the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the utility model.

[0043] It is to be understood that the terms "including", "comprising", "having" and their conjugates mean "including without limitation" and encompass the more appreciable inclusion mean the processes, methods, articles, or apparatuses that consist of those elements specifically listed.

[0044] It should be noted that the drawings are very simplified and use non-precise ratios, only to facilitate, clear and assist in the purpose of illustrating the embodiments.

[0045] The pipe connecting device provided by the utility model is used for connecting external pipes conveying fluid and connecting fluid conveying pipelines. The pipe connecting device mainly comprises a connecting body and a plurality of fastening nuts. The connecting body has at least two connecting pipes, each of which is provided with a bulging part. The bulging part is pressed into the external pipe, so that the connecting pipe (or the connecting body) is connected with the external pipe. Each connecting pipe is also provided with an external thread for thread connection with the fastening nut. The fastening nut is sleeved on the external pipe, and the inside of the fastening nut is provided with a clamping part. When the external pipe is connected with the connecting pipe and the fastening nut is screwed tightly with the connecting pipe, the fastening nut clamps and pushes the connecting part of the connecting pipe and the external pipe through the clamping part, so that the connecting pipe and the external pipe are fixedly connected, and double sealing is formed at the connecting part, thereby improving the stability of the sealing.

[0046] Embodiment one

[0047] Figure 1 The assembly diagram of the pipe connecting device in embodiment one is shown in Figure 2 The disassembly diagram of the pipe connecting device in embodiment one is shown in Figure 3 The sectional view of the pipe connecting device in embodiment one is shown in Figures 1 to 3 The pipe connecting device mainly comprises a connecting body 100 and a fastening nut 200. The connecting body 100 in this embodiment is a two-way pipe connecting structure, which has two connecting pipes 110 (the two connecting pipes are connected in a straight line in the drawing). The connecting body is connected with the external pipe 300 through each connecting pipe 110. The inner diameter of each connecting pipe 110 is consistent with the inner diameter of the external pipe connected therewith.

[0048] Each connecting pipe 110 is provided with a bulging part 111, which is located at the second end of the connecting pipe and is used for being pressed into the external pipe 300 to make the external pipe in a diameter-expanded state, so that the connecting pipe 110 is connected with the external pipe 300. Figure 4 The schematic diagram of the connecting body in embodiment one is shown inFigure 4 As shown, the bulge 111 is formed by the outer wall of the connecting pipe bulging outward, and the outer diameter of the bulge 111 is greater than the inner diameter of the outer pipe 300. When the bulge 111 is pressed into the outer pipe, the outer pipe 300 will exert a clamping pressure on the bulge 111, and the bulge 111 will exert an expansion pressure on the outer pipe 300. The outer pipe is in an expanded state, the bulge 111 is tightly fitted with the outer pipe 300, and the two interact with each other to form a friction force, thereby forming a connection between the connecting pipe 110 and the outer pipe 300 and not easy to loosen. Herein, each component or part is referred to as the first end or first side in the assembled state close to one end or one side of the connecting body 100, i.e. Figure 1 A direction of the connecting body 100, and the second end or second side is referred to as the second end or second side away from one end or one side of the connecting body 100, i.e. Figure 1 B direction in the connecting body 100.

[0049] The outer surface of the bulge 111 is composed of a first pressure receiving surface 111a, a second pressure receiving surface 111b and a third pressure receiving surface 111c. The first pressure receiving surface 111a is located at the first side of the bulge, the second pressure receiving surface 111b is located at the second side of the bulge, and the third pressure receiving surface 111c is located between the first pressure receiving surface 111a and the second pressure receiving surface 111b. The first pressure receiving surface 111a and the second pressure receiving surface 111b are conical curved surfaces, and in the direction along the connecting pipe and pointing to the second end of the connecting pipe, the outer diameter of the first pressure receiving surface 111a gradually increases, and the outer diameter of the second pressure receiving surface 111b gradually decreases. The third pressure receiving surface 111c is a cylindrical curved surface, and in the direction along the connecting pipe, the outer diameter of the third pressure receiving surface 111c is constant. In this embodiment, the outer diameter of the bulge 111 is always greater than the inner diameter of the outer pipe 300, and the outer diameter is the largest at the third pressure receiving surface 111c. When the bulge 111 is pressed into the inner part of the outer pipe 300, the interaction force between the bulge 111 and the outer pipe 300 at the third pressure receiving surface 111c is the largest, and the two are the most tightly fitted, therefore, the bulge 111 can form a seal with the outer pipe at the third pressure receiving surface 111c.

[0050] The bulge 111 is located at the second end of the connecting pipe, so when the connecting pipe is connected with the outer pipe 300, the bulge 111, particularly the second end port of the bulge 111 (or the second pressure bearing surface 111b) is first pressed into the outer pipe 300; in order to prevent the port from being deformed, separated from the inner wall of the outer pipe, and obstructing the fluid flow, etc. due to the impact of the opposite fluid, the end surface 111d of the port is designed as a tapered curved surface, and the inner diameter of the port has an expanding trend in the direction along the connecting pipe and pointing to the second end thereof; in this way, the pipe diameter is increased and the flow rate is slowed down at the second end port of the bulge, and the impact force of the fluid is weakened, and more importantly, the tapered curved surface 111d has a certain inclination, and the impact force of the opposite fluid will push the end surface 111d to expand the end surface 111d and make the second pressure bearing surface 111b tightly adhere to the inner wall of the outer pipe, so that the port is not deformed, separated from the inner wall of the outer pipe, and obstructed from the fluid flow.

[0051] In the first embodiment, the connecting pipe 110 is further provided with an external thread 112, which is arranged on the outer wall of the connecting pipe; the external thread 112 is located at the first side of the bulge. The maximum outer diameter of the bulge 111 (or the outer diameter of the third pressure bearing surface 111c) is smaller than the outer diameter of the external thread 112, so that the fastening nut can pass through the bulge and be screwed with the external thread 112 at the first side of the bulge.

[0052] The fastening nut 200 is sleeved on the outer pipe, and when the outer pipe is connected with the connecting pipe and the fastening nut on the outer pipe is screwed with the connecting pipe, the fastening nut clamps and pushes the connection between the connecting pipe and the outer pipe through the clamping portion thereof, and forms a seal. The number of fastening nuts in the pipe connecting device matches the number of connecting pipes of the connecting body, so the pipe connecting device in the first embodiment can be provided with two fastening nuts 200.

[0053] Figure 5 And Figure 6 is a sectional view of the fastening nut in the first embodiment. As shown in Figure 5 and Figure 6 , the fastening nut 200 has an internal thread 210 and a clamping portion 220; the internal thread 210 and the clamping portion 220 are located inside the fastening nut, wherein the internal thread 210 is arranged on the inner wall of the first end of the fastening nut and is used for screwing with the external thread 112 on the connecting pipe; the clamping portion 220 is a circular ring structure arranged on the inner wall of the fastening nut, and the clamping portion 220 is located at the second side of the internal thread 210. In the first embodiment, the clamping portion 220 is arranged on the inner wall of the second end of the fastening nut.

[0054] The inner diameter of the clamping portion 220 is not less than the outer diameter of the outer pipe, i.e. the inner diameter of the clamping portion 220 is equal to or greater than the outer diameter of the outer pipe, so that the outer pipe 300 can pass through the clamping portion 220 and the fastening nut 200 can be sleeved on the outer pipe.

[0055] Meanwhile, the inner diameter of the clamping portion 220 is also less than the composite outer diameter, which is the outer diameter of the bulging portion at the maximum position of the bulging portion pressed into the outer pipe, i.e. the composite outer diameter = the maximum outer diameter of the bulging portion + the wall thickness of the outer pipe; when the bulging portion 111 of the connecting pipe is pressed into the outer pipe 300 and connected with the outer pipe, the fastening nut sleeved on the outer pipe is screwed with the outer thread 112 on the connecting pipe through the inner thread 210, and the clamping portion 220 of the fastening nut approaches the bulging portion 111 from the second side of the bulging portion 111 and is clamped on the second pressure bearing surface of the bulging portion, so as to clamp and push the bulging portion pressed into the outer pipe at the second pressure bearing surface, so that a seal is formed between the bulging portion and the outer pipe at the second pressure bearing surface.

[0056] In the first embodiment, the fastening nut 200 and the connecting pipe also have a moderate fastening position; when the fastening nut 200 and the connecting pipe are screwed to the moderate fastening position, the clamping portion 220 is just clamped on the second pressure bearing surface of the bulging portion, clamps and pushes the bulging portion pressed into the outer pipe, and forms a seal between the bulging portion and the outer pipe at the second pressure bearing surface. If the fastening nut 200 and the connecting pipe are not screwed to the moderate fastening position, the clamping and pushing of the clamping portion 220 to the bulging portion pressed into the outer pipe at the second pressure bearing surface may not form an effective seal between the bulging portion and the outer pipe at the second pressure bearing surface; when the fastening nut 200 and the connecting pipe are screwed beyond the moderate fastening position, the clamping portion 220 may excessively squeeze and damage the elements of the outer pipe and the bulging portion.

[0057] The pipe connecting device has a positioning structure for indicating the moderate fastening position of the fastening nut and the connecting pipe; as shown in Figure 4 and Figure 6 The positioning structure includes an annular groove 230 arranged on the inner wall of the nut body and a continuous or discontinuous annular protrusion 113 arranged on the outer wall of the connecting pipe; the annular groove 230 is located at the first side of the inner thread 210, and the annular protrusion 113 is located at the first side of the outer thread 112. When the fastening nut 200 and the connecting pipe are at the moderate fastening position, the annular protrusion 113 is just located in the annular groove 230.

[0058] When the fastening nut 200 is screwed to the connection pipe to the moderate fastening position, the operator needs to exert a slightly larger screwing force to push the annular protrusion 113 into the annular groove 230, so that the operator can easily judge the moderate fastening position of the fastening nut and the fastening bolt through the change of the screwing force. When the fastening nut 200 is screwed to the connection pipe to the moderate fastening position, the annular protrusion 113 is just located in the annular groove 230, the clamping portion 220 is just clamped on the second pressure surface of the bulge portion, the bulge portion pressed into the outer pipe is clamped and pushed, and the second pressure surface of the bulge portion and the outer pipe are sealed.

[0059] At the same time, when the fastening nut 200 and the connection pipe are in the moderate fastening position, the annular protrusion 113 is located in the annular groove 230, and a slightly larger screwing force is needed to push the annular protrusion 113 out of the annular groove 230, so that the problem of loosening of the fastening nut can be effectively prevented.

[0060] In this embodiment, the shape and size of the annular protrusion 113 are matched with the annular groove 230, and the annular groove 230 and the annular protrusion 113 have a circular arc shape, which is smooth, so that the annular protrusion 113 can be pushed in or out of the annular groove 230.

[0061] In the first embodiment, the outer wall of the fastening nut 200 is further provided with a plurality of convex ridges 240, as shown in the figure. Figure 5 The convex ridges 240 are uniformly distributed on the outer wall of the fastening nut to facilitate the operator to hold or cooperate with the tool to perform the screwing operation.

[0062] In the first embodiment, the connection body, the fastening nut and the outer pipe are made of synthetic resin material; the synthetic resin material can be any one or more of PFA (tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, also known as perfluoroalkylate, soluble polytetrafluoroethylene), PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), ETFE (tetrafluoroethylene-ethylene copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PVC (polyvinyl chloride), PP (polypropylene), PE (polyethylene), PCTFE (polytrifluorochloroethylene), PEEK (polyether ether ketone), PSU (bisphenol A polysulfone), PPSU (polyphenylene sulfone) and PESU, PES (polyether sulfone).

[0063] Embodiment Two

[0064] The connection body 100 in the first embodiment is a two-way pipe connection structure, and the connection body 100 has two connection pipes, so that the pipe connection device in the first embodiment can be configured with two fastening nuts.

[0065] In the second embodiment, the connecting body 10 is a three-way pipe connecting structure, as shown in the figure, having three connecting pipes 11, each of which can be connected with different external pipes, so that the connecting pipes form a passage between different external pipes; the pipe connecting device can be provided with three fastening nuts. Figure 7

[0066] In the second embodiment, the connecting body 10 also has a cavity 12, and each connecting pipe 11 is in communication with the cavity 12. A valve body (not shown in the figure) can be arranged in the cavity 12, and the valve body is used to control the communication or disconnection of each connecting pipe with the cavity.

[0067] It should be noted that the connecting body in the present application can also be other multi-way pipe connecting structures to meet more complex pipe arrangement requirements, and the selection can be made according to the actual production application, and the present application does not limit this.

[0068] Although the content of the present application has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present application. After reading the above content, various modifications and substitutions of the present application will be obvious to those skilled in the art. Therefore, the protection scope of the present application should be defined by the appended claims.​

Claims

1. A pipe connection device, characterized in that The pipe connecting device comprises: a connecting body having at least two connecting pipes; each connecting pipe is provided with a bulge and an external thread; the bulge is located at the second end of the connecting pipe, and is used to press into the external pipe to make the external pipe in a diameter-expanded state, so as to form a connection between the connecting pipe and the external pipe; the external thread is arranged on the outer wall of the connecting pipe, and is used to be screwed with a fastening nut; the external thread is located at the first side of the bulge; a plurality of fastening nuts, which are sleeved on the external pipe; the fastening nut is provided with an internal thread and a clamping portion, which are located at the inner portion of the fastening nut; the internal thread is arranged on the inner wall of the first end of the fastening nut, and is used to be screwed with the external thread on the connecting pipe; the clamping portion is a circular ring structure arranged on the inner wall of the fastening nut, and is used to clamp and push the bulge pressed into the external pipe; the clamping portion is located at the second side of the internal thread; Each component has a first end or a first side close to one end or one side of the connecting body in the assembled state, and a second end or a second side away from one end or one side of the connecting body.

2. The pipe connecting device according to claim 1, wherein the bulge is formed by the outer wall of the connecting pipe bulging outwardly; the inner diameter of each connecting pipe is consistent with the inner diameter of the external pipe connected thereto.

3. The pipe connecting device according to claim 2, wherein the bulge has a first pressure receiving surface, a second pressure receiving surface and a third pressure receiving surface; the first pressure receiving surface is located at the first side of the bulge, the second pressure receiving surface is located at the second side of the bulge, and the third pressure receiving surface is located between the first pressure receiving surface and the second pressure receiving surface; the first pressure receiving surface and the second pressure receiving surface are conical curved surfaces; in the direction of the connecting pipe pointing to the second end thereof, the outer diameter of the first pressure receiving surface gradually increases, and the outer diameter of the second pressure receiving surface gradually decreases; the third pressure receiving surface is a cylindrical curved surface; in the direction of the connecting pipe, the outer diameter of the third pressure receiving surface is constant.

4. The pipe connecting device according to claim 3, wherein the outer diameter of the third pressure receiving surface is the maximum outer diameter of the bulge, and the bulge can form a seal with the external pipe at the third pressure receiving surface; the fastening nut clamps and pushes the bulge pressed into the external pipe at the second pressure receiving surface through the clamping portion thereof, so that the bulge also forms a seal with the external pipe at the second pressure receiving surface.

5. The pipe connecting device according to claim 1, wherein the maximum outer diameter of the bulge is smaller than the outer diameter of the external thread; the end surface of the bulge is a conical curved surface; in the direction of the connecting pipe and pointing to the second end thereof, the inner diameter of the port shows an expanding trend.

6. The pipe connecting device according to claim 1, wherein the inner diameter of the clamping portion is not less than the outer diameter of the external pipe, so that the external pipe can pass through the clamping portion, and the fastening nut can be sleeved on the external pipe; the inner diameter of the clamping portion is smaller than the composite outer diameter, so that the clamping portion can clamp and push the bulge pressed into the external pipe; the composite outer diameter is the maximum outer diameter of the bulge pressed into the external pipe.

7. The pipe connecting device according to claim 4, wherein the pipe connecting device has a positioning structure for indicating the appropriate fastening position of the fastening nut and the connecting pipe. When the fastening nut and the connecting pipe are in the moderate fastening position, the clamping portion just clamps on the second pressure surface of the bulging portion, clamps and pushes the bulging portion pressed into the outer pipe, and forms a seal between the bulging portion and the outer pipe at the second pressure surface.

8. The pipe connecting device according to claim 7, wherein the positioning structure comprises an annular groove arranged on the inner wall of the nut body and an annular protrusion arranged on the outer wall of the connecting pipe. The annular groove is located on the first side of the inner thread. The annular protrusion is located on the first side of the outer thread. When the fastening nut and the connecting pipe are in the moderate fastening position, the annular protrusion just locates in the annular groove.

9. The pipe connecting device according to claim 8, wherein the annular protrusion is matched with the annular groove in shape and size. The annular groove and the annular protrusion are circular in cross section.

10. The pipe connecting device according to claim 1, wherein the connecting body further has a cavity, and each connecting pipe is in communication with the cavity. A valve body is arranged in the cavity, and the valve body is used to control the communication or disconnection between each connecting pipe and the cavity. The connecting body is a two-way or multi-way pipe connecting structure. ​ ​ ​

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