Pressure tank for gas-powered vehicle

Abstract

Pressure tank (1) for storing gas for installation in a gas-powered vehicle, having a rotationally symmetrical, elongated shape, cylindrical in the central region and closed at both ends with domed end caps, and having a wall enclosing a cavity (2) for storing the gas, as well as a metallic connection piece, a so-called boss (4), at each of the end caps, wherein the wall comprises a reinforcing layer (6) made of fiber-reinforced plastic and an inner liner (3), wherein a bushing (7, 7') connected to the boss (4) via a screw thread (12) and a pressure ring (8, 8', 8'') are provided for sealing, designed such that the pressure ring (8, 8', 8'') is pressed against the liner (3) by a spring force and the liner (3) is thereby pressed against the boss (4) in a pressure area (13), the spring force being supported on the bushing (7, 7').and wherein the boss (4) has several radial ribs (10) on its inner surface (4a) which extend at least partially into the pressure area (13) and which press into the liner (3) in such a way that they counteract a twisting between boss (4) and liner (3).

Description

[0001] The invention relates to a pressure tank for storing gas for installation in a gas-powered vehicle, wherein the pressure tank has a rotationally symmetrical, elongated shape, cylindrical in its central region and terminated at both ends with domed end caps. The pressure tank has a wall enclosing a cavity for storing the gas and a metallic connector, a so-called boss, at each end cap. The wall comprises a reinforcing layer made of fiber-reinforced plastic and an inner liner. For sealing, a bushing connected to the boss via a screw thread and a pressure ring are provided, designed such that the pressure ring is pressed against the liner by a spring force, thereby pressing the liner against the boss within a pressure zone, with the spring force being supported by the bushing.

[0002] The invention further relates to a precursor for the manufacture of such a pressure tank, as it exists before the application of the reinforcing layer. The precursor comprises at least one liner and one boss. For sealing, it includes a bushing connected to the boss via a screw thread, a pressure ring, and a spring element, designed such that the spring element bears against the bushing and presses the pressure ring against the liner, thereby pressing the liner against the boss within a pressure zone.

[0003] Gas-powered vehicles, for example, use a gas engine or a fuel cell with an electric motor as their drive system. To store sufficient fuel, the gas, which can be hydrogen, is stored under high pressure in a tank. Typical pressures for such tanks are over 200 bar, often up to 700 bar, and sometimes even up to 800 bar. This means that the pressure tank must not only be gas-tight under this pressure, but also require high mechanical stability.

[0004] Pressure tanks for gas-powered vehicles are known in the prior art. These pressure tanks have a wall that includes an inner liner, for example made of thermoplastic, for sealing purposes, and a reinforcing layer made of fiber-reinforced plastic to provide mechanical stability. The reinforcing layer is usually wound and made of carbon fiber reinforced plastic (CFRP).

[0005] The boss has a through-hole and a threaded connection. At least one of the two bosses has a tank fitting attached, allowing the pressure tank to be filled or gas to be withdrawn in a controlled manner. On the other boss, the through-hole is sealed with a cap, or another tank fitting or a safety valve is provided there.

[0006] A good and durable seal at the transition between the boss and the liner is of paramount importance. This is particularly challenging with larger hydrogen pressure tanks, such as those required for fuel cell-powered commercial vehicles. These tanks can reach diameters of up to 700 mm and lengths of 2500 mm. Many existing sealing concepts are insufficient in such cases.

[0007] WO 2022 / 136045 A1 describes a pressure tank that has the aforementioned features. To improve the tightness of the finished pressure tank, a pressure ring is used, which is pressed against the liner by a spring element supported by a bushing connected to the boss.

[0008] However, state-of-the-art designs have the disadvantage that they are not adequate for all load conditions and can therefore damage the seal. During the manufacturing process, when winding the reinforcement layer, the bond between the boss and the liner is subjected to particularly high stress. In some cases, this stress loosens or damages the bond, leading to subsequent leaks.

[0009] The object of the invention is now to develop a pressure tank or a pre-product described above for such a pressure tank, which ensures improved tightness at the connection between boss and liner and in which this connection has better stability in the manufacturing process, especially when winding the reinforcement layer.

[0010] The problem is solved, firstly, by a pressure tank according to claim 1. Further advantageous features are mentioned in the respective dependent claims.

[0011] According to the invention, the pressure tank according to claim 1 is characterized in that the boss has several radial ribs on its inner surface which extend at least partially into the pressure area and which engage in the liner in such a way that they counteract a twisting between boss and liner.

[0012] Radial ribs are defined as narrow, elongated ridges on the inner surface of the boss, extending essentially along their length in the radial direction R. This maximizes the surface area that resists twisting between the boss and the liner. The effect of the radial ribs can be specifically tailored to the circumferential forces to be absorbed by adjusting their height, length, and number.

[0013] A significant advantage of the embodiment according to the invention is that circumferential forces acting on the boss can be better transferred to the liner by means of these radial ribs.

[0014] This stabilizes the connection with respect to torque and distributes forces more evenly into the liner, ensuring a more reliable and durable seal. The connection is not weakened by circumferential forces occurring during manufacturing, assembly, or subsequent operation of the pressure tank.

[0015] Particularly during the production of the reinforcing layer, which takes place on a winding machine, the connection between the boss and the liner is subjected to high torques. The rotation of the pre-product during the winding process is driven by the boss. There is always a risk that the boss will rotate or loosen, thus damaging the connection.

[0016] Similarly, during operation of the pressure tank, a circumferential load can act upon it, which could loosen the connection between the boss and the liner. The design according to the invention also counteracts this and, through the positive locking mechanism, prevents relative rotation between the boss and the liner, which would otherwise lead to damage to the liner. Thus, the seal is permanently ensured.

[0017] Due to the spring force and the two-part design with bushing and pressure ring, a preload can be applied in the pressure zone between the boss and the liner to ensure a seal. This spring force can be applied by a separate spring element between the bushing and pressure ring or by a spring-loaded pressure ring itself. This preload ensures sufficient sealing even under low internal pressure or during expansion due to temperature differences. By precisely adjusting the spring force, over-compression of the liner and the resulting deformation that could lead to leaks can be avoided. Even a small preload ensures that the liner rests against the boss, allowing the radial ribs to engage with the liner. It is important that the radial ribs extend at least partially into the pressure zone where the pressure ring presses the liner against the boss.

[0018] The radial ribs are preferably designed to extend between 20 and 40 mm in the radial direction R and to have at least four, and preferably at least six, radial ribs. This design ensures that the circumferential forces are distributed and that the compressive stress caused in the liner by the radial ribs under the expected torques does not become locally excessive. For example, with a typical plastic used for the liner (PA6), care should be taken to ensure that the compressive stress ideally does not exceed 40 MPa, and in any case not exceeds 70 MPa. Otherwise, the liner will undergo local plastic deformation and thus be damaged.

[0019] To achieve good force transmission between the radial ribs and the liner, it is advantageous if the radial ribs have a height between 1.5 and 5 mm, especially between 2 and 4 mm.

[0020] To prevent the anti-rotation feature from becoming insufficient if the liner lifts slightly from the boss's inner surface, for example due to shrinkage, it is advantageous if the radial ribs extend at least 5 mm, preferably at least 10 mm, of their radial length within the pressure zone, or if they are entirely within the pressure zone. The pressure zone here is the area where the liner is pressed against the inside of the boss by the pressure ring.

[0021] In a particularly preferred version, the screw thread is designed such that the boss has an internal thread and the bushing has an external thread, which mesh together. This allows for a particularly compact connection design.

[0022] By screwing the bushing into the boss, the spring between the bushing and the pressure ring, or the spring-loaded pressure ring itself, is compressed. The spring force and thus the preload can be precisely adjusted by the spring design and the intended screw-in depth during assembly (until the device reaches its limit).

[0023] To ensure proper preload build-up and a good seal, the pressure ring is displaceable relative to the bushing in the direction of the longitudinal axis L. The pressure ring can be made sufficiently rigid to achieve uniform contact pressure across its surface and thus a reliable seal. For added stiffness and stabilization, the pressure ring can have an additional cylindrical section on its outer circumference.

[0024] Alternatively, the pressure ring itself can be designed as a spring element, in particular as a spring ring, for example in the form of a conical disc. This means that the pressure ring itself provides the spring force to press the liner in place when it is supported by the bushing and pressed against the liner.

[0025] Preferably, the bushing is arranged so that it does not have full-surface contact with the liner. The sealing pressure is transferred to the liner only via the surface of the pressure ring.

[0026] Furthermore, the bushing can have a collar against which the spring element or the spring-loaded pressure ring is supported, the collar being arranged essentially perpendicular to the longitudinal axis L of the pressure tank. This ensures good ease of assembly and good force transmission.

[0027] A spring element, as used here, is an element capable of generating sufficient elastic spring force when compressed. The same applies to the resilient compression ring. For example, they can be designed as ring-shaped or disc-shaped elements made of spring steel, featuring so-called spring wings. In particular, the spring element can have a U-shaped or V-shaped cross-section. Alternatively, the spring element can also be formed from several leaf springs or coil springs arranged between the bushing and the compression ring. Other types and shapes of springs can also be used. In particular, the spring element can be designed as a so-called disc spring. The disc spring can have one or more spring plates. The spring force can be adjusted, among other things, by the number of spring plates arranged in series.

[0028] To ensure improved contact pressure, the inner surface of the boss in the pressure area is preferably oriented essentially perpendicular to the longitudinal axis. This allows the spring force to be optimally utilized as contact force.

[0029] In another particularly advantageous embodiment, the pressure ring has at least one circumferential groove in the pressure area, and the liner has at least one circumferential rib that engages in the groove. This prevents the liner from being pulled out between the pressure ring and the boss. Such radially acting forces occur when the liner is exposed to significant temperature changes. For example, the liner shrinks during annealing. Larger temperature differences can also occur during operation.

[0030] If the liner manufacturing process allows, this groove can have a dovetail cross-section. This improves the positive fit and also prevents the liner from lifting off the pressure ring. For example, if the liner is manufactured using blow molding, the grooves can be dovetail-shaped. The plastic used in liner manufacturing fills the groove and forms the corresponding circumferential rib.

[0031] Larger pressure tanks, in particular, have a boss at both end caps. Therefore, it is especially desirable to provide a sealing set with a bushing and pressure ring, as described above, at each end cap of the pressure tank to improve the seal between the liner and the respective boss.

[0032] Furthermore, the invention relates to a precursor for the manufacture of the previously described pressure tanks. The precursor comprises at least one liner and one boss. It can also be only a part of the liner that later forms the inner wall of the pressure tank. This is the case, for example, when the liner is manufactured by injection molding and is assembled from several parts, such as two end caps and cylindrical center sections.

[0033] In particular, the pre-product can comprise the complete liner and two bosses with appropriate connection and sealing via the previously described design.

[0034] For the intermediate product, the problem is solved by an embodiment according to claim 13. Further advantageous embodiments are described in the corresponding dependent claims.

[0035] According to the invention, the preliminary product is characterized in that the boss has several radial ribs on its inner surface, which extend at least partially into the pressure area and engage in the liner in such a way that they counteract a twisting between the boss and the liner and can therefore absorb circumferential forces and torque.

[0036] Furthermore, it is advantageous if the radial ribs are designed in such a way that a large proportion of the torques occurring during the winding of the reinforcement layer can be absorbed and transmitted. This can be achieved by adjusting the number, height, and length of the radial ribs accordingly.

[0037] Winding the reinforcement layer is a further process step in the manufacture of pressure tanks, in which the pre-product consisting of liner and boss is wrapped with strips or tapes made of fiber-reinforced plastic, particularly CFRP (carbon fiber reinforced plastic). These strips or tapes contain a large number of rovings and are preferably already impregnated with a suitable resin, which is cured after winding. The faster the winding process, the more rovings are processed simultaneously, and the more viscous the resin, the higher the tensile stress of the strips or tapes must be during winding.

[0038] This means that with an improved connection between the boss and liner, which can withstand higher circumferential forces, it becomes possible to wind even faster and with more rovings simultaneously, even with high resin toughness. The solution according to the invention thus also offers an improvement in the productivity of pressure tank production. In particular, the solution according to the invention can withstand torques up to 500 Nm and allows winding with a winding tension of 1000 N. The solution according to the invention is particularly advantageous for so-called towpreg winding, but is equally advantageous for wet winding.

[0039] Further advantageous features of the invention are explained using exemplary embodiments with reference to the drawings. These features can be advantageously implemented not only in the combination shown, but also individually combined with one another. The figures show in detail: Fig. 1 Schematic representation of a pressure tank according to the invention Fig. 2 Schematic representation of the connection and sealing between boss and liner in an embodiment according to the invention Fig. 3a,b Detailed representation of the sealing set for two embodiments according to the invention Fig. 4a,b Detailed view of the boss with radial ribs Fig. 5 Further embodiment of a precursor according to the invention for the production of a pressure tank Fig. 6a,b Top view of the circumferential rib on the liner and of the pressure ring with groove

[0040] The figures are described in more detail below. Identical reference numbers denote identical or analogous parts or components.

[0041] The Fig. Figure 1 shows the pressure tank 1 with a boss 4 at each of its two end caps. A tank fitting 5 for filling and controlled gas release is screwed into one boss 4. The other boss 4 is sealed with a cap. Alternatively, it can accommodate a safety valve. The wall of the pressure tank 1 encloses the cavity 2 and is formed by an inner liner 3 and a reinforcing layer 6. The liner 3 is preferably made of thermoplastic material such as polyamide and is manufactured, for example, by blow molding or injection molding (optionally assembled from several parts). The reinforcing layer 6 is produced by a winding process using tapes of fiber-reinforced plastic, preferably CFRP. The pressure tank 1 is rotationally symmetrical about its longitudinal axis L. Particular attention must be paid to the seal between the boss 4 and the liner 3 in such pressure tanks.Especially with large pressure tanks, such as those required in commercial vehicles to ensure sufficient range, achieving a good and lasting seal is a significant challenge. Additionally, the connection is subjected to considerable stress during the winding of the reinforcing layer. It must therefore be sufficiently robust to withstand this stress as well.

[0042] Fig. Figure 2 shows an enlarged section of the pressure tank 1, so that the inventive design for improved sealing becomes apparent. The seal against the internal gas pressure in the pressure tank is achieved by pressing the liner 3 against the boss 4 due to the spring force of the spring element 9 and due to the internal gas pressure itself.

[0043] The sealing set, consisting of bushing 7, pressure ring 8, and spring element 9, is shown. Pressure ring 8 and spring element 9 are located inside the liner 3, i.e., in the cavity 2. The spring element 9 is pre-tensioned via bushing 7, which is connected to boss 4 by the screw thread 12. This spring element presses pressure ring 8 against the liner 3, and thus presses the liner 3 against boss 4. The radial ribs 10 on boss 4 are not explicitly shown in this illustration. The liner 3 is pressed against boss solely by pressure ring 8. This pressure ring 8 is movable relative to bushing 7 and can be shifted along the longitudinal axis L. In the illustrated version, they together enclose spring element 9, thus providing good protection. This design also facilitates easy assembly of the components. In this version, spring element 9 is a disc spring.Shown is a disc spring with two spring plates; however, a single spring plate or multiple spring plates can also be used. The spring force can be varied by adjusting the spring's thickness and material, as well as the number of spring plates. The clamping force can be adjusted to the desired level by selecting the appropriate spring element and the screw-in depth on the threaded section 12. Other spring elements than those shown in this example can also be used in the embodiment according to the invention.

[0044] The radial ribs 10, which are pressed into the liner, prevent the boss 4 from twisting relative to the liner 3. This allows circumferential forces, such as those occurring during the winding process in the production of the reinforcement layer, to be effectively absorbed. During the winding process, the pre-product consisting of liner 3 and boss 4 is driven by the boss 4, causing it to rotate and wind the CFRP strips or tapes onto the liner 3 with the appropriate tensile tension. The forces applied via the boss 4 are transferred directly to the liner 3 via the radial ribs 10. This prevents the connection between the boss 4 and the liner 3 from twisting or loosening.

[0045] It is important that the radial ribs 10 are at least partially located within the pressure area 13, where the liner 3 is pressed against the inner surface 4a of the boss by the pressure ring 8. Larger temperature changes, for example during annealing, can cause the liner 3 to shrink and tend to lift away from the boss 4. The pressure ring 8 ensures that the anti-rotation mechanism provided by the radial ribs 10 remains effective even in such a case.

[0046] The inner surface 4a of the boss is oriented essentially perpendicular to the longitudinal axis L in the pressure area 13, where the liner 3 is pressed against the boss 4. The surface of the pressure ring 8, which is pressed against the liner 3, is also oriented essentially perpendicular to the longitudinal axis L. Additionally, the collar 17 of the bushing, against which the spring element 9 is supported, is arranged essentially perpendicular to the longitudinal axis L. Thus, the spring force of the spring element 9 is completely transmitted via the pressure ring 8 to the sealing surface between the boss 4 and the liner 3 by means of the screw connection 12.

[0047] Alternatively, sufficient force transmission can still be achieved by tilting these surfaces at a maximum angle of + / - 20°. Tilting the sealing surface also contributes to better venting of the sealing surface during liner manufacturing. The tilt allows air to escape more easily from the compression point during pressing.

[0048] The Boss 4 also features the so-called wing 4b, which tapers outwards, thus achieving a stepless transition in the reinforcement layer between Boss 4 and Liner 3. Furthermore, the Boss 4 has an internal thread 11, through which a tank fitting, a safety valve, or a closure can be screwed. The pressure tank is filled and emptied via the through-hole 16 in the Boss.

[0049] Fig. 3a and Fig. Figure 3b schematically shows the connection and sealing on liner 3 in detail. Fig. 3a shows the execution as in Fig. 2. Also shown are the radial ribs 10, which are located on the inner surface 4a of the boss and extend at least partially into the pressure area 13. The pressure area 13 is the area in which the pressure ring 8 presses the liner 3 against the boss 4. The illustration shows a version in which the radial ribs 10 are located entirely within the pressure area 13.

[0050] In Fig. Figure 3b shows a variant of the sealing set, which consists of bushing 7', pressure ring 8', and spring element 9. The pressure ring 8' is essentially designed as a disc. It may have a small cylindrical section on its inner diameter, which serves for axial guidance. This design offers the advantage that the components of the sealing set can be more compact and lighter.

[0051] Furthermore, the schematic shows that the surface of the pressure ring 8', which presses against the liner 3, can have a certain inclination. Additionally, the surface on the boss 4 in the pressure area could also have an inclination. With an inclination of these surfaces of a maximum of + / - 20°, sufficient force transmission can still be achieved. The inclination of the sealing surface also contributes to better venting of the sealing collar during liner manufacturing and assembly. The inclination allows air to escape more easily from the pinch point.

[0052] This tendency can also be observed in the solution according to Fig. 3a / b must be present. On the other hand, the solution according to Fig. 4a / b the surface of the pressure ring 8 is designed vertically.

[0053] In this version, spring element 9 is designed as a disc spring. A disc spring with four spring plates is shown; however, fewer spring plates, a single spring plate, or multiple spring plates can also be used. The spring force can be adjusted to the desired value by changing the thickness, material, and number of spring plates.

[0054] In the illustrated embodiments, the bushing 7,7' has the collar 17, which is oriented essentially perpendicular to the longitudinal axis L, and on which the spring element 9 is supported.

[0055] Fig. 4a and Fig. Figure 4b shows the boss 4 in detail, once from the side with liner 3 and once in perspective. The radial ribs 10, which are indented into the liner 3, are clearly visible. They extend as narrow, elongated protrusions arranged radially, essentially in the radial direction R. This provides the largest possible surface area for absorbing circumferential forces. A certain deviation from the radial direction R is acceptable.

[0056] The number, height, and length of the radial ribs 10 can be designed to adapt the anti-rotation feature to the expected torques during winding of the reinforcement layer 6. Six radial ribs 10 are shown here. A design with four or five radial ribs, or even more, is also possible. The radial length of the radial ribs is preferably between 20 and 40 mm to absorb sufficient circumferential forces while ensuring that the compressive stress in the liner does not become too high.

[0057] In order for the radial ribs 10 to engage well with the liner 3 and for the liner 3 not to lift off later, they must be at least partially located in the pressure area 13, in which the pressure ring 8,8',8" presses the liner 3 against the boss 4.

[0058] Fig. Figure 5 shows a further embodiment according to the invention, here using the example of the intermediate product 18. The boss 4 with a portion of the liner 3 and the mounted sealing set are shown. The intermediate product 18 can comprise only a portion of the liner. Alternatively, the intermediate product 18 can comprise the entire liner 3 and preferably a second boss 4 and a further sealing set on the second boss 4. The sealing set is here composed of a bushing 7' and a pressure ring 8'', wherein the pressure ring 8'' is pressed against the liner 3 by the spring element 9, which is supported on the bushing 7'.

[0059] In an alternative variant not shown, the pressure ring itself can be designed as a spring element. In this way, the pressure ring can exert the spring force through its own spring tension when it is supported against the bushing 7' and pressed by it against the liner 3. For example, in this case, the pressure ring 8 can be designed as a conical disc made of spring steel.

[0060] Several radial ribs 10 are provided on the inner surface 4a of the boss, engaging with the liner 3 and thus forming an anti-rotation device between the boss 4 and the liner 3. Crucially, according to the invention, the radial ribs 10 are located at least partially within the pressure zone 13, where the pressure ring 8'' presses the liner 3 against the boss 4. This is the only way to ensure that the radial ribs 10 engage the liner 3 with sufficient form-fit and can effectively absorb circumferential forces. This is necessary, for example, when the liner 3 shrinks due to temperature changes and thus lifts slightly away from the boss 4, as occurs during annealing or with significant temperature fluctuations during operation. This design prevents the boss 4 and liner 3 from twisting relative to each other during this lifting and re-engaging process. Overall, it is sufficient if a portion of the length of the radial ribs 10 is located within the pressure zone 13, as illustrated here.In particular, it is sufficient if at least approximately 30% of the radial length of the radial ribs 10 is located in the pressure area 13. With a preferred length of 30 mm for the radial ribs 10, a length of approximately 10 mm located in the pressure area 13 would be sufficient.

[0061] The preferred height of the radial ribs 10 is between 1.5 and 5 mm. In particular, it is 3 mm here.

[0062] Furthermore, the pressure ring has a groove 14 located in the pressure area 13, extending circumferentially. Correspondingly, the liner 3 has a circumferential rib 15 in this area, which engages positively in the groove 14, thus preventing the liner 3 from being pulled out between the pressure ring 8' and the boss 4. This prevents damage to the connection between the liner 3 and the boss 4 during tempering, which would impair the seal.

[0063] In Fig. Figure 6 shows a preferred embodiment for the groove 14 and the circumferential rib 15. For illustration, the following are shown in Fig. 6a the top view of the circumferential rib 15 of the liner 3 and in Fig. Figure 6b shows a top view of the groove 14 in the pressure ring 8'. The circumferential rib engages positively in the groove 14. This prevents the liner 3 from being pulled out of the clamping force of the pressure ring 8'' in a radial direction. Such radial forces can be caused, for example, by temperature differences. In particular, during the tempering of the tank, the liner shrinks due to these temperature differences. However, larger temperature fluctuations can also occur during operation, with differences of up to 60 or 80°C. Reference symbol list 1 pressure tank 2 cavities 3 Liner 4 Boss 4a Inner surface of the boss 4b Boss's Wing 5 Tank fitting 6 Reinforcing layer 7.7' socket 8.8',8'' pressure ring 9 spring element 10 radial rib 11 internal threads 12 screw threads 13 Print area 14 Nut 15 Circumferential rib 16 through holes 17 collars 18 Precursor L Longitudinal axis of the pressure tank R Radial direction of the pressure tank QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2022 / 136045 A1

[0007]

Claims

[1] Pressure tank (1) for storing gas for installation in a gas-powered vehicle, having a rotationally symmetrical, elongated shape, cylindrical in the central region and closed at both ends with domed end caps, and having a wall enclosing a cavity (2) for storing the gas, and a metallic connection piece, a so-called boss (4), at each of the end caps, wherein the wall comprises a reinforcing layer (6) made of fiber-reinforced plastic and an inner liner (3), wherein a bushing (7, 7') connected to the boss (4) via a screw thread (12) and a pressure ring (8, 8', 8'') are provided for sealing, designed such that the pressure ring (8, 8', 8'') is pressed against the liner (3) by a spring force and the liner (3) is thereby pressed against the boss (4) in a pressure area (13), the spring force being supported on the bushing (7, 7'), characterized by, that the boss (4) has several radial ribs (10) on its inner surface (4a) which extend at least partially into the pressure area (13) and which press into the liner (3) in such a way that they counteract a twisting between boss (4) and liner (3). [2] Pressure tank (1) according to claim 1 characterized by that the radial ribs (10) extend between 20 and 40 mm in radial direction R and that at least four, preferably at least six radial ribs (10) are provided. [3] Pressure tank (1) according to claim 1 or 2 characterized by , that the radial ribs (10) are located in the pressure area (13) with at least 5 mm, preferably at least 10 mm of their radial extent, and in particular are located completely in the pressure area (13). [4] Pressure tank (1) according to any of the preceding claims characterized by , that the screw thread (12) on the boss is designed as an internal thread and on the bushing (7,7') as an external thread. [5] Pressure tank (1) according to any one of the preceding claims characterized by , that the pressure ring (8,8',8'') is displaceable relative to the bushing (7,7') in the direction of the longitudinal axis L, and that the spring force with which the pressure ring (8,8',8'') is pressed against the liner (3) can be changed via the screw-in depth of the bushing (7,7') into the boss (4). [6] Pressure tank (1) according to any one of the preceding claims characterized by , that the pressure ring (8'') is designed as a spring element, in particular as a spring ring, so that it can exert the spring force when preloaded by the bushing (7,7'). [7] Pressure tank (1) according to any of the preceding claims characterized by , that the spring force on the pressure ring (8,8',8'') is applied by a spring element (9) which is designed as a separate component. [8] Pressure tank (1) according to claim 7 characterized by , that the spring element (9) is designed as a so-called disc spring, wherein one or more spring discs are present. [9] Pressure tank (1) according to any one of the preceding claims characterized by , that the bushing (7,7') has a collar (17) on which the spring element (9) or the resilient pressure ring (8'') is supported, the collar (17) being oriented substantially perpendicular to the longitudinal axis L. [10] Pressure tank (1) according to any of the preceding claims characterized by , that the inner surface (4a) of the boss in the pressure area (13) is oriented essentially perpendicular to the longitudinal axis L. [11] Pressure tank (1) according to any of the preceding claims characterized by , that the pressure ring (8,8',8'') in the pressure area (13) has at least one groove (14) extending in the circumferential direction, and that the liner (3) has at least one circumferential rib (15) engaging in the groove (14). [12] Pressure tank (1) according to claim 11 characterized by , that the groove (14) has a dovetail-shaped cross-section. [13] Precursor for the manufacture of a pressure tank (1) according to one of the preceding claims, comprising at least one liner (3) and one boss (4), wherein a bushing (7, 7') connected to the boss (4) via a screw thread (12) and a pressure ring (8, 8', 8'') are provided for sealing, designed such that the pressure ring (8, 8', 8'') is pressed against the liner (3) by a spring force and the liner (3) is thereby pressed against the boss (4) in a pressure area (13), wherein the spring force is supported on the bushing (7, 7'), characterized by , that the boss (4) has several radial ribs (10) on its inner surface (4a) which extend at least partially into the pressure area (13) and which press into the liner (3) in such a way that they counteract a twisting between boss (4) and liner (3).

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