Description:
The present invention relates to high-pressure gas containment systems, specifically focusing on Type 4 composite pressure cylinders used for storing compressed natural gas (CNG) or hydrogen. It introduces a threaded valve integration mechanism that utilizes a parallel-threaded profile within a centrally positioned metallic boss. The system enables superior sealing, lower torque requirements, and enhanced mechanical reliability compared to conventional tapered-thread systems.

BACKGROUND OF THE INVENTION
Type 4 pressure cylinders, characterized by their lightweight polymeric liner and composite overwrap, are widely used in various sectors including automotive, transportation, and industrial gas handling. These cylinders feature metallic bosses that serve as interfaces for gas valves and regulators.
Conventional designs use tapered thread systems (e.g., NPT or BSPT), which rely on metal-to-metal contact for sealing. This configuration presents multiple challenges:
• High torque during valve installation
• Risk of radial stress-induced fatigue
• Reduced reusability due to thread deformation
• Inconsistent sealing, especially under pressure cycling
The present invention addresses these problems through the introduction of a parallel-threaded boss design that enables consistent sealing, reusability, and reduced wear.
SUMMARY OF THE INVENTION
The invention proposes a valve integration system for composite pressure cylinders in which a metallic central boss is internally threaded with a 1.125-12 UNF 12B parallel thread profile. A metallic gas valve with matching male threads is inserted and sealed using an elastomeric O-ring located near the thread root.
This thread configuration offers:
• Constant diameter across the thread length
• Uniform axial stress distribution
• Significantly lower assembly torque
• A high-integrity, leak-proof seal independent of thread deformation
This solution is especially suitable for applications requiring frequent valve servicing or replacement.

BRIEF DESCRIPTION OF DRAWINGS
1. Figure 1 – Exploded view showing the Type 4 cylinder, central boss, and valve components
2. Figure 2 – Cross-sectional view of the metallic boss with internal parallel threads
3. Figure 3 – Enlarged view of valve engagement and O-ring sealing interface
4. Figure 4 – Torque application illustration during valve installation
5. Figure 5 – Stress distribution comparison: tapered vs. parallel threads

DETAILED DESCRIPTION OF THE INVENTION
1. Boss and Cylinder Construction
• The boss is made from high-strength materials such as aluminum alloy 7075-T6 or stainless steel (e.g., AISI 316L).
• It is embedded into the polymeric liner during cylinder fabrication, followed by external fiber reinforcement.
• The boss includes a central bore that is precision-machined with a 1.125-12 UNF 12B parallel thread profile.
2. Thread Geometry
• Thread Type: Unified National Fine (UNF), Class 2B
• Major Diameter: 1.125 inches
• Thread Pitch: 12 threads per inch
• Thread Angle: 60°
• Engagement Length: 6–8 full turns
• The parallel thread ensures no radial expansion or stress concentration, improving fatigue life and structural integrity.
3. Valve Configuration and Interface
• The valve incorporates external 1.125-12 UNF 2A threads and a machined sealing surface.
• An elastomeric O-ring (Viton, EPDM, or equivalent) is housed in a groove at the boss face.
• During engagement, the O-ring is axially compressed, forming a primary gas-tight seal.
4. Assembly Process
• The valve is aligned with the boss and inserted manually.
• Torque in the range of 30 to 60 Nm is applied using a calibrated wrench.
• The O-ring is compressed between the valve shoulder and the boss sealing surface.
• The thread serves solely for mechanical retention, not sealing.
5. Advantages of the Invention
Feature Proposed Parallel Thread System Conventional Tapered Thread
Sealing Method Axial O-ring Metal-to-metal or PTFE tape
Assembly Torque Low (30–60 Nm) High (80–120 Nm)
Reusability 50+ cycles <10 cycles
Stress Distribution Axial and uniform Radial and localized
Fatigue Resistance High Moderate
Maintenance Easy Risk of cross-threading, galling
6. Leak Prevention and Long-Term Performance
• The sealing interface remains consistent over multiple cycles due to the separation of mechanical fastening and sealing functions.
• Optional PTFE tape or liquid thread sealants may be used for secondary protection if needed.
• The sealing system is capable of handling cyclic internal pressure without degradation.
7. Applicability and Integration
• The design can be adapted to any composite cylinder with a central boss, including variants used in vehicles, medical gas handling, or industrial storage.
• It is compatible with conventional valve manufacturing techniques and does not require special equipment for installation.
8. Testing and Validation
• Leak Testing: Helium leak tests under pressure demonstrated zero leakage within detection limits.
• Torque-Fatigue Tests: Over 500 cycles of valve installation and removal showed no damage or degradation.
• Hydrostatic and Pressure Cycling Tests: Sustained performance under simulated service conditions confirmed system robustness.
• This invention relates to a novel and technically enhanced valve integration system for Type 4 composite pressure cylinders, particularly aimed at storing high-pressure gases such as Compressed Natural Gas (CNG) and hydrogen. These cylinders typically comprise a polymeric liner encased in a fiber-reinforced composite shell, with a metallic boss fitted at one or both ends to accommodate a valve or other accessories. The invention specifically improves upon the interface between the valve and the central metallic boss using parallel thread technology, which offers significant advantages over traditional tapered threading systems in terms of performance, reliability, and longevity.
• The system primarily consists of a valve with externally threaded parallel threads (specifically 1.125-12 UNF 12B threads) that engage seamlessly with internally threaded parallel grooves machined into a centrally placed metallic boss. This boss is embedded within the polymeric neck of the liner and serves as the interface for the valve. Unlike conventional systems that use tapered threads, which rely on thread interference and compression for sealing, the present invention employs parallel threads which enable a uniform, full-length thread engagement that enhances sealing performance while reducing installation torque and mechanical stress.
• As depicted in Figure 1, the invention starts with an exploded view showing the main components of the cylinder system: the composite-wrapped cylinder body, the polymeric liner, the embedded metallic boss, and the valve. The exploded format demonstrates the positional relationship and axial alignment of each component, with the valve intended to screw into the central boss. The design is inherently modular, allowing for ease of assembly, disassembly, and maintenance.
• Moving into Figure 2, we examine a detailed cross-sectional view of the central metallic boss. The internal threads of the boss are clearly illustrated as having a constant pitch and root diameter, confirming their parallel (non-tapered) configuration. This precise thread profile plays a crucial role in ensuring consistent engagement with the valve threads. The parallel nature of the threads allows for uniform torque distribution during valve tightening, reducing localized stress and minimizing the risk of mechanical deformation of the polymeric liner or the boss itself. Additionally, this configuration offers better thread durability and reusability over multiple installations.
• Figure 3 complements the previous figure by focusing on the external threading of the valve stem. This drawing emphasizes the compatibility between the valve and boss threading system. Both follow the same parallel threading specification, ensuring tight and full-depth engagement over the entire threaded length. The absence of a taper ensures that the threads do not bind excessively, thereby lowering the torque required for insertion and removal. This not only enhances assembly efficiency but also reduces wear and tear on the thread surfaces.
• In Figure 4, the process of valve installation is shown in operational form. The valve is aligned and torqued into the central boss using a calibrated torque wrench. This figure highlights the torque path and the angular direction of rotation, typically clockwise. Importantly, the torque applied does not induce radial stress on the neck of the liner, a common issue with tapered threads. This reduced radial load prolongs the life of both the liner and the boss, especially under cyclic pressurization and thermal variation. The system is engineered to deliver repeatable installation outcomes, ensuring that gas-tightness and safety standards are consistently met.
• Figure 5 presents a vital comparative view between traditional tapered threading and the proposed parallel thread system. On the left side of the diagram, the drawbacks of tapered threads are visually communicated: excessive radial force, non-uniform contact zones, and difficulty in achieving repeatable sealing without over-torquing. These issues are particularly pronounced in Type 4 cylinders, where polymeric liners are susceptible to stress-induced cracking. The right side of the figure illustrates the even distribution of force and consistent engagement offered by the parallel threads. This configuration ensures high sealing performance without inducing stress on surrounding materials, thereby eliminating the need for additional sealants or post-tightening calibration.
• Altogether, the presented system introduces a superior valve integration strategy that resolves key limitations of existing tapered thread-based designs. The use of 1.125-12 UNF parallel threads, machined with high precision in both the valve and the boss, offers an efficient, leak-proof, and maintenance-friendly alternative that is particularly suitable for modern composite cylinders. Moreover, the design enhances operational safety, enables reusability, and provides a robust platform for next-generation gas storage systems.
• By integrating this improved parallel-threaded interface, the invention offers a paradigm shift in the design and reliability of Type 4 composite cylinders, ensuring compatibility with high-pressure applications while significantly enhancing the mechanical integrity of the valve-boss-liner assembly.

, Claims:Disclosed is a parallel-threaded valve engagement system for composite gas cylinders featuring a centrally embedded metallic boss. The boss is machined with a 1.125-12 UNF 12B internal thread, and the valve is sealed using an elastomeric O-ring located near the thread root. This design minimizes torque requirements, eliminates metal fatigue associated with tapered threads, and ensures reusability and consistent gas-tight performance across multiple operational cycles.