Bosses for pressure tanks and pressure tanks for gas-powered vehicles

Abstract

A boss (4,4') for a pressure tank (1) for storing gas in a gas-powered vehicle, the boss (4,4') being suitable for attachment to a wall of the pressure tank (1), the wall having a hollow chamber (2) for storing gas, the wall having a reinforcing layer (6) made of fiber-reinforced plastic and an inner located liner (3) for sealing, the boss (4,4') having an external thread (10) connectable to a matching internal thread of the liner (3). As well as a pressure tank (1) having two such bosses (4,4').

Description

Technical Field

[0001] The present invention relates to a pressure tank for storing gas for assembly in a gas-powered vehicle, the pressure tank having a rotationally symmetric elongated shape that is cylindrical in an intermediate region and closed at both ends by arched end caps. The pressure tank has a wall portion surrounding a hollow chamber for storing gas and a metallic connection member, so-called boss, provided on each end cap, the wall portion including a reinforcing layer made of fiber-reinforced plastic and an inner liner for sealing.

[0002] Furthermore, the present invention relates to a boss for such a pressure tank.

[0003] A gas-powered vehicle has, for example, a gas engine or a fuel cell equipped with an electric motor as a drive device. A gas, which can be, inter alia, hydrogen, is stored in the tank under high pressure so that sufficient fuel can be stored. Typically for such a pressure tank, the pressure exceeds 200 bar and often reaches up to 600 bar, indeed in some cases up to 700 bar or 875 bar. That is, the pressure tank not only has to be airtight under this pressure but also requires high mechanical stability.

[0004] In the prior art, pressure tanks for gas-powered vehicles are known. Such a pressure tank has a wall portion that includes an inner liner, for example made of a thermoplastic resin, for sealing and a reinforcing layer made of fiber-reinforced plastic for obtaining mechanical stability. Preferably, the reinforcing layer is wound and configured as a CFK layer. CFK represents carbon fiber-reinforced plastic.

[0005] The boss has a through hole and connecting threads. A tank fitting is connected to at least one of the two bosses, enabling the filling of a pressure tank or the controlled extraction of gas from a pressure tank. In the other boss, the through opening is sealed by a closure, or another tank fitting or safety valve is provided on this other boss.

[0006] In such pressure tanks, particular attention must be paid to the metal connecting members, specifically the joints between the bosses and the liner. This is because large forces are generated at these joints during manufacturing, and high airtightness requirements are imposed when mechanical loads are applied during subsequent operation, when internal pressure fluctuates, and when there are large temperature fluctuations. This is a particularly significant challenge for large hydrogen pressure tanks with a total mass exceeding 150 kg.

[0007] Various solutions known in the prior art exist for bonding between a boss and a liner. For example, as shown in European Patent Application Publication No. 550951, a shape-coupled joint can be used between the liner (referred to as the inner lining) and the boss (referred to as the annular flange). However, such shape-coupled joints, such as a dovetail joint, can currently only be manufactured when the pole caps of the liner are manufactured by injection molding or a similar method.

[0008] It would be advantageous if shape-matching joints could be formed using methods other than injection molding.

[0009] Other known possibilities are disclosed in German Patent Application Publication No. 102011010685, International Publication No. 2011 / 103687, and European Patent Application Publication No. 2115343. In these possibilities, a boss (referred to as a base or metal body) is screwed onto a liner flange (referred to as an inner container or core container). For this purpose, the boss has internal threads. The seal is ensured by a metal cylinder screwed into the boss, which supports an O-ring seal. Thus, the liner is tightened between the outer boss and the inner metal cylinder. A reinforcing layer made of CFK is then wrapped around the outer surface of the boss.

[0010] These known configurations have the disadvantage of causing difficulties during the manufacture of the reinforcement layer, particularly in relatively large pressure tanks such as those required for commercial vehicles to be powered by fuel cells, where the bosses are not sufficiently fixed in place. Such novel pressure tanks for commercial vehicles can reach diameters of up to 600 mm and lengths of 2500 mm. The reinforcement layer is usually manufactured by a winding method. For this, a liner, already bonded to the bosses as a pre-product, is tightened and rotated in a winding machine. Torque is introduced to the liner through one or more bosses. Sliver or fiber roving is wound around the liner. In this case, a high tensile force acts on the liner tangentially due to the draw tension of the roving or sliver resulting from the process. Therefore, a large torque acts on the joint between the bosses and the liner during winding. The lever arm increases with diameter, and since multiple rovings are wound simultaneously in relatively large pressure tanks, the load becomes correspondingly higher in relatively large pressure tanks. Conventional known joint configurations cannot withstand this increased force. Damage to the joint between the liner and the boss can lead to mechanical failure or a loss of airtightness.

[0011] The object of the present invention is to devise a pressure tank or a boss for a pressure tank that has a better connection between the liner and the boss, thereby enabling the easy and reliable manufacture of novel, relatively large pressure tanks.

[0012] The above problem is solved, firstly, by the boss described in claim 1. Other advantageous features are listed in the respective dependent claims.

[0013] According to the present invention, the boss described in claim 1 is characterized in that the boss has a male thread, the male thread may be coupled to a suitable female thread of the liner, and the male thread is arranged concentrically with respect to the longitudinal axis L of the pressure tank. By using the male thread provided on the boss for coupling, the diameter of the boss-liner coupling can be increased without the need to increase the diameter of the through hole in the boss, thereby increasing its load capacity. By increasing the thread diameter of the male thread, the coupling can transmit a higher torque.

[0014] Furthermore, the male threads on the boss, and consequently the good connection between the boss and the liner, work to prevent any force from being applied to the sealing surface between the liner and the boss. This is possible because the male threads are set further radially away from the longitudinal axis t than the sealing surface, and consequently any torque load is set further away from the sealing surface located further inside. Moreover, the enlarged diameter of the connection between the boss and the liner can also enlarge the sealing surface located further inside between the boss and the liner, resulting in a better seal.

[0015] When the male thread has at least 4 to a maximum of 10 threads, a particularly good connection is produced in a space-saving and, consequently, weight-reduced configuration. In this specification, a single notch that completes one turn around the circumferential surface, consisting of a threaded ridge with adjacent threaded recesses, is considered a thread.

[0016] In a particularly preferred configuration, the male thread is formed as a cylindrical thread, having a diameter of at least 60 mm, preferably at least 90 mm, and up to 180 mm, with respect to the tip of the threaded portion. This ensures sufficient load-bearing capacity for the joint for the subsequent winding process, while also allowing for a boss that is not excessively heavy.

[0017] Furthermore, it is advantageous that the male thread has at least one incomplete thread at one end, with a thread ridge lower than another thread ridge, and at the other end, at least one incomplete thread, preferably at least one complete thread, with a thread recess smaller than another thread recess. In particular, the height of the thread ridge decreases linearly toward one end of the thread; that is, the thread ridge decreases continuously toward its one end. In particular, the depth of the thread recess decreases linearly toward the other end of the thread; that is, the thread recess decreases continuously toward the other end. The thread pitch can be locally adapted to the thread ridge or thread recess.

[0018] Particularly preferable are threads with low thread ridges located at the end facing the hollow chamber, and threads with small thread recesses located at the end facing the reinforcing layer. The female threads of the liner are configured in opposite directions accordingly.

[0019] These special threads form a shape-matching joint between the boss and the liner, increasing the stability of the connection. When the boss is screwed into the liner, the modified incomplete or complete threads at each end of the threads allow for repeatable determination of the boss's rotational position relative to the liner. As a result, the male threads on the boss are precisely filled by the female threads on the liner when screwed in, thereby achieving a connection that can withstand high loads. Furthermore, even in bosses with low manufacturing precision that are not fully screwed in, no large gap remains in the threads between the boss and the liner. This is because each thread recess at the end of the threads has a smaller volume. This is advantageous because, if the gap in the connection is large, the immense internal pressure would normally act on the liner with high shear forces, damaging it.

[0020] One preferred possibility for good mounting of a pressure tank in a vehicle or tank module is to configure the boss such that the boss includes a neck region for housing within a holder. The holder surrounds the neck region of the boss, thereby being able to support the weight of the pressure tank. This offers advantages over the conventional mounting of pressure tanks using fastening belts on the wall of the pressure tank.

[0021] In particular, the neck region has a length that is at least 50% of the outer diameter when measured at its narrowest point, preferably 40 mm to 80 mm, and especially preferably the neck region is formed with a cylindrical outer contour over this length. This ensures that the neck region is long enough to form a stable housing portion in the holder.

[0022] In another configuration according to the present invention, the boss further has an annular sealing surface that is positioned perpendicular to the longitudinal axis (L) or forms an angle of 70° to 110° with the longitudinal axis (L). The sealing is further improved as a liner may be additionally pressed against this sealing surface, for example by a spring element.

[0023] In particular, the boss may have a threaded hole configured as a female thread, through which a bushing can be screwed. This bushing acts to press the liner against the sealing surface of the boss by a spring element.

[0024] The above problem is solved, on the other hand, by the pressure tank described in claim 8. Other advantageous features are listed in the respective dependent claims.

[0025] The pressure tank according to the present invention is characterized in that the pressure tank includes two bosses according to the present invention. Thus, both bosses are coupled via male threads to a liner having female threads that fit these male threads. Such a pressure tank can be manufactured, for example, by first forming a pre-product. The liner is manufactured from a thermoplastic resin, particularly polyamide, for example by blow molding, and then both bosses are screwed into the liner.

[0026] In another method step, a tape made of fiber-reinforced plastic, particularly CFK (carbon fiber reinforced plastic), is wrapped around a pre-product manufactured from a liner and a boss to form a reinforcing layer of the pressure tank. The tape is preferably already immersed in a suitable plastic resin (so-called towpreg) that is cured after wrapping. Such towpreg provides even higher tensile force during wrapping because, based on a viscous resin, towpreg requires a relatively high pulling force to unwind from the storage bobbin. The boss configuration according to the present invention allows the connection with the liner to be subjected to significantly more load than in conventional connections, thereby ensuring smooth wrapping without damaging the connection in any case.

[0027] Furthermore, it is advantageous if one boss has a right-hand thread and the other boss has a left-hand thread, and the liner has correspondingly fitting female threads on each side. This allows both boss-liner connections to withstand relatively high rotational forces in a single common direction of rotation, thereby providing better protection against twisting during the winding process. Thus, in this configuration, the drive during the winding process can be performed via both bosses.

[0028] Alternatively, both bosses may be configured with male threads in the same direction of rotation (either both bosses have right-hand threads, or both bosses have left-hand threads). This allows the product and pressure tank to withstand torque in both directions of rotation, with one of the bosses receiving the torque each time.

[0029] Preferably, the female thread that fits the male thread of the liner is manufactured by cutting in the liner. This enables the formation of accurately fitting female threads, which enhances the sealing and load resistance of the joint. Furthermore, the risk of crack formation during the screwing of the boss is reduced because the male thread does not need to bite into the surface of the liner.

[0030] The sealing between the liner and the boss can be improved when a bush coupled to the boss for sealing, a pressing ring, and a spring element are provided, and the spring element is supported by the bush to press the pressing ring against the liner and thereby press the liner against the sealing surface of the boss.

[0031] In a preferred variant, the bush is attached to the boss via a threaded thread, and in particular, the force applied to the pressing ring can be changed via the bush. Thus, for example, the bush may have a male thread that engages with the female thread provided in the boss. By screwing the bush into the boss to various depths, the spring between the bush and the pressing ring can be compressed with various strengths. Therefore, the preload can be intentionally adjusted.

[0032] Alternatively, the bush may be attached to the boss via a fastening portion. In this case, the fastening portion must be configured so that it cannot be released by a spring force.

[0033] A bushing that can be coupled to a boss, a compression ring, and a spring element may be positioned on a so-called blow pin during the production of the liner by blow molding. In blow molding, the plastic for the liner is extruded from a nozzle, which first creates a tube. Then, two or more parts of a blow molding tool are combined to form a cavity in the shape of the liner to be formed for the pressure tank. The extruded tube is located within this cavity. Gas is blown into the tube through a so-called blow pin, or nozzle, which presses the tube against the inner surface of the blow molding tool. This gives the liner the desired shape. After the plastic material has solidified, the liner can be demolded. The blow pin is removed. Preferably, the liner is made from a thermoplastic material, such as polyamide. Thermoplastic plastics solidify after cooling. This allows the compression ring and spring element to be positioned on the inner surface of the liner after the liner has been manufactured, and when the bushing is later coupled to the boss, the spring element, supported by the bushing, can press the compression ring against the liner and press the liner against the surface of the bushing.

[0034] The main advantage of this configuration is that, based on a spring element and a two-part configuration comprising a bushing and a compression ring, a preload for sealing can be applied to the sealing surface between the liner and the boss. The sealing surface is located in the region where the liner is pressed against the boss. Based on the preload thus formed, sufficient sealing is always provided, for example, when the internal pressure is small or when expansion occurs due to temperature differences. Furthermore, by adjusting the spring force, excessive compression of the liner and subsequent deformation that would lead to non-sealing can be avoided.

[0035] A spring element, as understood herein, is an element capable of applying sufficient elastic spring force when compressed. For example, a spring element may be formed as an annular element made of spring steel having a so-called "spring plate (Federfluegel)," and in particular, the spring element may have a U-shaped or V-shaped cross-section. Alternatively, a spring element can be formed from a plurality of leaf springs or coil springs positioned between a bush and a compression ring. Other types and shapes of springs can also be used. As other spring materials, spring elements made of elastic polymers (elastomers or crosslinked thermoplastics) or fiber composite plastics can be used.

[0036] To ensure continuous function, it is advantageous for the compression ring, together with the bushing, to completely surround the spring element. Thus, the spring element is protected and remains in the desired position. Furthermore, this configuration also offers simpler assembly. These advantages are particularly beneficial when the liner is already formed using blow molding. "Completely surround" in this sense applies even when individual openings or gaps still exist; complete sealing is not required.

[0037] To ensure proper preload formation and good sealing, the compression ring is movable relative to the bushing in the direction of the longitudinal axis L. Therefore, the compression ring can be configured rigidly to achieve uniform compression across the sealing surface and, consequently, a reliable seal.

[0038] Preferably, the bushing is positioned so as not to be in planar contact with the liner. The crimping for sealing is transmitted only through the surface of the pressure ring.

[0039] Another advantageous feature of the present invention will be described with reference to the drawings based on embodiments. Each of the listed features is advantageously realized not only in the illustrated combinations, but may also be combined with each other individually. [Brief explanation of the drawing]

[0040] [Figure 1] This is a schematic diagram of the pressure tank according to the present invention. [Figure 2] This is a detailed diagram showing the joint between the boss and the wall in the configuration according to the present invention. [Figure 3] This figure shows a boss according to the present invention, which has male threads. [Figure 4] This is a schematic diagram showing the special male threads of the boss according to the present invention.

[0041] The drawings are described in more detail below. Identical or similar components or parts are given the same reference numeral.

[0042] Figure 1 shows a pressure tank 1 with one boss 4, 4' at each of the polar caps. A tank fitting 5 for filling, controlling, and withdrawing gas is screwed into boss 4. Boss 4' is sealed by a closure. Alternatively, the boss can accommodate a safety valve. The wall of the pressure tank 1 surrounds a hollow chamber 2 and is formed by an internally located liner 3 and a reinforcing layer 6. The liner 3 is preferably made of a thermoplastic plastic, such as polyamide, and is manufactured by blow molding in the method according to the present invention. The reinforcing layer 6 is manufactured by a tape winding method, preferably of fiber-reinforced plastic, CFK. The pressure tank 1 is rotationally symmetric about the longitudinal axis L. In such a pressure tank, particular attention must be paid to the sealing and joints between bosses 4, 4' and the liner 3. Good coupling between bosses and liners is a major challenge, especially in large pressure tanks, such as those required in commercial vehicles to allow for sufficient cruising distance. According to the present invention, bosses 4 and 4' are screw-fastened to the liner 3 via male threads. Preferably, one boss 4 has a right-hand thread, and the other boss 4' has a left-hand thread.

[0043] Figure 2 shows a magnified view of a portion B of the pressure tank 1, where the configuration according to the present invention for improving the coupling between the boss and the liner can be seen. The boss 4 has male threads 10. The liner 3 has correspondingly fitting female threads. Preferably, these female threads are manufactured by machining after the liner 3 is formed, for example, by blow molding. Based on the relatively large diameter of the male threads 10, the coupling can withstand relatively large loads. Thus, smooth wrapping of the tape for the reinforcing layer 6 is possible.

[0044] Additionally, the boss has a sealing surface 4.2. The compression ring 8 and spring element 9 are located inside the liner 3, i.e., within the hollow chamber 2. A preload is applied to the spring element 9 via a bushing 7 coupled to the boss 4, and the spring element 9 presses the compression ring 8 against the liner 3, and in turn presses the liner 3 against the boss 4. The connection between the boss 4 and the bushing 7 is formed via a threaded hole 12, on which the bushing 7 has a corresponding male thread. The bushing 7 and the liner 3 are not in planar contact, but only some contact occurs at the end face of the liner 3. The liner 3 is pressed against the sealing surface 4.2 of the boss only via the compression ring 8. This compression ring 8 is movable relative to the bushing 7 and can be moved in the direction of the longitudinal axis L. Together the compression ring 8 and the bushing 7 surround the spring element 9, thereby protecting the spring element 9 well. Furthermore, this ensures that these components are properly assembled. For this purpose, a special tool is used that can be inserted through the through-hole of boss 4.

[0045] The surface of the pressure ring 8 that presses against the liner 3 and the surface of the liner 3 that presses against the boss 4 are oriented substantially perpendicular to the longitudinal axis L. Similarly, the flange of the bushing 7 that supports the spring element 9 is positioned substantially perpendicular to the longitudinal axis L. Thus, the spring force of the spring element 9 is fully transmitted through the pressure ring 8 to the sealing surface between the boss 4 and the liner 3 by the screw fastening portion 12. The inclination of these surfaces, particularly the sealing surface 4.2, of up to + / -20°, ensures that sufficient force transmission is always achieved. Furthermore, the inclination of the sealing surface 4.2 contributes to better degassing from the sealing flange during liner manufacturing. This inclination allows air to leak more effectively from the crushed area when the mold halves are assembled.

[0046] The area of ​​boss 4 in which the pressure ring 8 presses the liner 3 against the boss 4 is called the sealing surface 4.2 or the clamping position (Drosselstelle). The sealing of the gas pressure within the pressure tank, and thus the clamping, is achieved by the compression of the liner 3 against boss 4 based on the spring force of the spring element 9 and the gas pressure itself.

[0047] The compression ring 8 is preferably shaped so that the largest possible contact surface is used for force transmission on the side in contact with the spring element 9. In this case, the compression ring 8 has a curved shape corresponding to the arc of a spring ring having a U-shaped cross-section.

[0048] For the configuration according to the present invention, spring elements other than those shown and used as examples herein may also be used.

[0049] Furthermore, the boss 4 is provided with female threads 11 through which, for example, tank fittings, safety valves, or closures can be screwed. The boss also has a neck region 4.1 that is suitable for housing a pressure tank in a holder for mounting it to a vehicle.

[0050] The configuration according to the present invention, which includes a male thread 10 on the boss for secure and stable coupling with the liner 3, can also be used in configurations different from the boss configuration shown herein. Therefore, for example, the sealing between the liner 3 and the boss 4 at the sealing surface 4.2 can be improved by other means, or the sealing can be performed in a form different from the shown pressing ring 8.

[0051] Figure 3 illustrates the configuration of a boss 4 according to the present invention, which includes a male thread 10 for coupling with a liner, a sealing surface 4.2, and a neck region 4.1. A flange is located between the neck region 4.1 and the male thread 10, and tape for a reinforcing layer is later wrapped around the flange, which is positioned between the reinforcing layer and the liner in the finished pressure tank. Preferably, the male thread 10 is a cylindrical thread. The diameter of the male thread 10 is preferably 60 mm to 180 mm.

[0052] The sealing surface 4.2 is positioned such that the liner is pressed against this sealing surface by an appropriate device, thereby creating a sealed clamping position against internal pressure.

[0053] Additionally, the sealing surface 4.2 may be provided with annular ridges a few tenths of a millimeter in height. These ridges press into the liner they are in contact with and thus contribute to a better seal.

[0054] Furthermore, the boss has a neck region 4.1 suitable for housing in a holder for mounting a pressure tank to a vehicle. Preferably, the neck region is configured with a cylindrical outer contour and has a length b of at least 50% of its outer diameter a.

[0055] Figure 4 shows a cross-sectional view of the special male thread 10 according to the present invention of the boss 4. The threaded ridge 10.1 extends to the outer diameter d and has the same height except for the threaded ridge 10.4. Similarly, the threaded recess 10.2 has the same depth except for the threaded recess 10.3. Each notch that makes up one full turn, consisting of the threaded ridge 10.1 and the threaded recess 10.2, forms one thread. The male thread 10 shown here has seven threads.

[0056] An incomplete or complete thread at one end of the male thread has a threaded ridge 10.4 having a smaller height. In particular, the height of each threaded ridge may decrease linearly toward this end of the male thread. This end faces the hollow chamber 2 of the pressure tank.

[0057] The other end of the male thread facing the reinforcing layer or the flange of the boss 4 is provided with an incomplete or complete thread having a thread recess 10.3 of less depth. In particular, the thread recess may be configured to decrease linearly toward this end of the male thread.

[0058] Based on the special configuration of the threads, a liner with correspondingly adapted opposite threads may be screwed over such that the rotational positioning is precisely predetermined, which provides the aforementioned advantages. [Explanation of symbols]

[0059] 1. Pressure tank 2 Hollow chamber 3 Raina 4,4' Boss 4.1 Neck Area 4.2 Sealing surface 5 Tank fittings 6. Reinforcement layer 7 Bush 8. Compression ring 9 Spring elements 10 Male screw thread 10.1 Threaded protrusion 10.2 Thread recess 10.3 Thread recess 10.4 Threaded protrusion 11 Female thread 12 threaded screws a. Outer diameter of the neck region b. Length of the neck area d Diameter of the male screw thread L Longitudinal axis of the pressure tank and boss R Pressure tank and boss radial direction

Claims

1. A boss (4, 4') for a pressure tank (1) for storing gas in a gas-powered vehicle, suitable for coupling to a wall surrounding a hollow chamber (2) for storing the gas in the pressure tank (1), wherein the wall includes a reinforcing layer (6) made of fiber-reinforced plastic and an internally located liner (3) for sealing, in the boss (4, 4'), The boss (4, 4') has a male thread (10), which can be coupled to a suitable female thread of the liner (3), and the male thread (10) is positioned concentrically with respect to the longitudinal axis (L) of the pressure tank (1). The male thread (10) has at least one incomplete thread at one end, which has a thread ridge (10.4) that is lower than another thread ridge (10.1), and at the other end, which has at least one incomplete thread with a thread recess (10.3) that is smaller than another thread recess (10.2). The threads having the low threaded protrusions (10.4) are located at the end facing the hollow chamber (2), and the threads having the small threaded recesses (10.3) are located at the end facing the reinforcing layer (6), and the female threads of the liner (3) are configured in the exact opposite direction to the male threads (10). Boss (4,4').

2. The boss (4, 4') according to claim 1, wherein the male thread (10) has at least 4 to a maximum of 10 threads.

3. The boss (4, 4') according to claim 1 or 2, wherein the boss (4, 4') includes a neck region (4.1) for housing within the holder, the neck region (4.1) having a length (b) which, when measured at the narrowest part of the neck region, is at least 50% of the outer diameter (a), the length (b) being 40 mm to 80 mm, and the neck region (4.1) is formed to have a cylindrical outer contour over the length (b).

4. The boss (4, 4') according to any one of claims 1 to 3, wherein the male thread (10) is configured as a cylindrical thread, and the diameter (d) of the male thread is at least 60 mm and at most 180 mm with respect to the tip of the threaded protrusion (10.1).

5. The boss (4, 4') according to any one of claims 1 to 4, wherein the boss (4, 4') has an annular sealing surface (4.2) which is positioned perpendicular to the longitudinal axis (L) or forms an angle of 70° to 110° with respect to the longitudinal axis (L).

6. The boss (4, 4') has a threaded hole (12) configured as an internal thread, through which a bush (7) can be screwed, and the bush (7) acts by a spring element (9) to press the liner (3) against the sealing surface (4.2) of the boss (4, 4') according to any one of claims 1 to 5.

7. A pressure tank (1) for storing gas, to be installed in a gas-powered vehicle, wherein the pressure tank (1) has a rotationally symmetrical elongated shape that is cylindrical in the middle region and closed at both ends by arched pole caps, and the pressure tank (1) has a wall portion surrounding a hollow chamber (2) for storing gas, and one metal connecting member, so-called boss (4, 4'), provided on each pole cap, and the wall portion includes a reinforcing layer (6) made of fiber-reinforced plastic and an inner liner (3) for sealing, in the pressure tank (1), A pressure tank (1) characterized in that both bosses (4, 4') are configured as described in any one of claims 1 to 6.

8. The pressure tank (1) according to claim 7, wherein one of the bosses (4) has a male thread (10) configured as a right-hand thread, and the other boss (4') has a male thread (10) configured as a left-hand thread.

9. The pressure tank (1) according to claim 7 or 8, wherein the female threads of the liner (3) that fit the male threads (10) are manufactured in the liner by cutting.

10. A pressure tank (1) according to any one of claims 7 to 9, wherein for sealing purposes, a bush (7) coupled to the boss (4, 4'), a pressing ring (8), and a spring element (9) are provided, the spring element (9) being supported by the bush (7) pressing the pressing ring (8) against the liner (3), and thereby pressing the liner (3) against the sealing surface (4.2) of the boss.

11. The pressure tank (1) according to claim 10, wherein the pressing ring (8) together with the bush (7) completely surrounds the spring element (9).

12. The pressure tank (1) according to claim 10 or 11, wherein the pressing ring (8) is movable relative to the bush (7) in the direction of the longitudinal axis (L).

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