Patent Description:
Pressure vessels may be used to compress and store many different gaseous substances. The compressed gas is used in a variety of applications, such as vehicle fuel and industrial applications, and as such, the pressure vessels can be designed for safe transportation and refill capability. In order to achieve acceptable volumetric efficiency and aid in transport and storage, the gas should be compressed to store a great amount of mass in a small area to achieve a high density. To maintain a high density, the gas should be stored at a very high pressure.

Many pressure vessels that store and transport compressed gas include end fittings to connect the pressure vessel to a valve, adapter, coupling, or plug. End fittings are used to fill, empty, or seal the pressure vessel and can interface with a smaller cross-sectioned tube extending from a larger cross-sectioned body of the pressure vessel. The fitting is made of two parts, a stem that reaches inside of the tube and a cap that fits outside of the tube. At high pressures, stored, compressed gas within the pressure vessel can impose large forces on the end fitting, with the result of a potential disengagement of the end fitting. This disengagement or disconnection would restrict function of the pressure vessel, as leaks of the compressed gas would occur. Thus, precautions should be taken to ensure that end fittings are sufficiently fixed to the pressure vessel.

Many end fittings, for example, end fittings used with high pressure hydraulic and pneumatic hoses, include a barbed stem that is inserted into the hose and an outer shell that is crimped onto the hose. Increased retention force is achieved by adding barbs onto the stem of the end fitting and then crimping the outer shell onto the hose to surround the barbed stem. The barbs can also be used to create interference with the liner or inside of a tubular or pressure vessel. Once crimped, the barbs fit tightly against the corrugated tubing or body of the pressure vessel, and the separate parts are held together by a crimped cap. However, as certification standards typically use minimum design failure pressure to be two to three times higher than the working pressure, this technique may not be sufficient to retain end fittings in higher pressure systems.

<CIT> discloses a pressure vessel, comprising: a pressure element defining a cavity with a wide portion and a narrow portion, the pressure element configured to store compressed gas; and an end fitting extending into the cavity of the pressure element, the end fitting comprising: a stem extending through the narrow portion and the wide portion; a cap surrounding the narrow portion of the pressure element and the stem at a location external to the pressure element.

<CIT> discloses pressure vessel, comprising: a pressure element defining a cavity with a wide portion and a narrow portion, the pressure element configured to store compressed gas; and an end fitting extending into the cavity of the pressure element, the end fitting comprising: a stem extending through the narrow portion and the wide portion; and a cap surrounding the narrow portion of the pressure element and the stem at a location external to the pressure element.

The present invention relates to the feature combination of the independent claim(s). Preferable embodiments are provided in the dependent claims.

The disclosure relates to a pressure vessel assembly including a pressure element storing compressed gas and a shell enclosing the pressure element and capture the compressed gas that permeates from the pressure element. The pressure vessel assembly including an end fitting extending into a cavity of the pressure element and from the pressure element through the shell. The end fitting including a stem that extends out from the shell in one direction and into the cavity of the pressure element in an opposite direction and a cap that surrounds the pressure element and the stem at a location external to the pressure element. The pressure vessel assembly including a retention component sustaining engagement of the end fitting with at least one of the pressure element or the shell below a predetermined pressure threshold.

The stem may include one or more barbs that lock the stem in a fixed position in relation to the pressure element. The stem may further include holes extending through a surface of the stem, venting the compressed gas as the stem moves out of the cavity, and reducing pressure on the end fitting. The retention component may be an anchor positioned proximate to an end of the stem and positioned at a location within the cavity of the pressure element, and the anchor may include one or more arms for preventing removal of the stem from the cavity of the pressure element below the predetermined pressure threshold. The one or more arms of the anchor may include an edge that is flat, blunt, sharp, or any combination thereof, and the edge may puncture the pressure element above the predetermined pressure threshold. The stem may further include holes extending through the stem and venting the compressed gas to a pressure level below the predetermined pressure threshold as the stem moves out of the cavity and before the edge of the one or more arms punctures the pressure element. The stem may further include a first ridge positioned between the end of the stem and the anchor, and the first ridge fails and allows movement of the anchor as the anchor contacts the first ridge. The stem may further include a second ridge spaced from the first ridge, and the second ridge may be closer to the end of the stem than the first ridge, the second ridge configured to stop movement of the anchor as the anchor contacts the second ridge.

The retention component may be an adhesive plug, and the adhesive plug and the stem may be directly couple at a fixed position within the cavity of the pressure element and to prevent end fitting disengagement below the predetermined pressure threshold. The cap may be a first cap, and the retention component may include a bulkhead assembly including a second cap surrounding the pressure element and the stem at a location internal to and abutting an interior surface of the shell. The bulkhead assembly may include a third cap surrounding the stem at a location external to and abutting an exterior surface of the shell and a first collar coupling to the second cap. The first collar may distribute pressure applied to the second cap to the shell. The bulkhead assembly may include a second collar coupling to the third cap, and the second collar may clamp the shell between the second collar and the first collar. The bulkhead assembly may include one or more screws tightening or loosening the first and second collars in respect to the shell or in respect to the second or third caps. The retention component may include a tether with a first end coupled to the stem at a location external to the shell and a second end coupled to a curved portion of another pressure element interior to the shell.

The disclosure further relates to a pressure vessel assembly including a pressure element defining a cavity with a wide portion and a narrow portion, and the pressure element stores compressed gas. The pressure vessel assembly may include an end fitting extending into the cavity of the pressure element, and the end fitting may include a stem extending through the narrow portion and the wide portion and a cap surrounding the narrow portion of the pressure element and the stem at a location external to the pressure element.

The stem may include one or more barbs that lock the stem in a fixed position in relation to the pressure element. The narrow portion may include corrugations that align with the one or more barbs, and the cap may be crimp-able around the narrow portion so that the cap conforms to the corrugations, the one or more barbs, or both. The cap may include indents positioned to align with the corrugations and the one or more barbs, and the cap may be crimp-able around the narrow portion and the stem so that a tight fit forms between the corrugations, the one or more barbs, and the indents. When the cap crimps around the stem and the narrow portion at the corrugations, the cap may stretch axially so that the tight fit is formed between the pressure element and the stem.

The disclosure further relates to a pressure vessel assembly including pressure elements for storing compressed gas and a shell enclosing the pressure elements. The shell captures the compressed gas that permeates from the pressure elements. The pressure vessel assembly includes an end fitting extending through the shell and into a cavity of the pressure elements, and the end fitting includes a stem having a first end and a second end. The first end extends into the cavity of the pressure elements, and the second end extends out through the shell. The stem has a hollow portion so that the compressed gas is passable through the stem. The end fitting includes a tube fixed to the first end of the stem that distributes adhesive supplied through the hollow portion of the stem, and the distributed adhesive retains the end fitting within the pressure elements.

The pressure vessel assembly may further include an adhesive plug formed by the distributed adhesive, positioned between the stem and the pressure elements, and used to retain the end fitting within the pressure elements. The stem may further include barbs locking the stem in a fixed axial position in relation to the pressure elements so that the adhesive plug forms below a distal end of the tube. The cavity of the pressure elements may include a narrow portion and a wide portion, and the wide portion may house the tube and the adhesive plug. The narrow portion may include corrugations aligned along the barbs of the stem, and the corrugations may interface with the barbs of the stem so that the stem holds in a fixed axial position. The pressure vessel assembly may further include a cap crimp-able around the narrow portion of the pressure elements so that the second end of the stem is secured by the cap, and the cap and the adhesive plug may prevent the end fitting from moving radially relative to the pressure elements.

The end fitting retention features disclosed herein are designed to increase retention capacity beyond what is provided by barbs alone. Several techniques of increasing retention capacity of the end fittings to pressure vessels are disclosed. One technique includes drilling small holes into sides of a stem portion of the end fitting. If the end fitting including the holes in the stem begins to disengage from the pressure vessel, gas will be released through the holes to decrease the pressure below the maximum retention capacity of the end fitting, slowing and/or stopping disengagement of the end fitting from the pressure element.

Another technique of retaining end fittings to pressure elements includes adding an anchor assembly to the end fitting. Once the end fitting is pushed through smaller-diameter tubing into the wide portion of the pressure element, the anchor assembly is seated into the wide portion of the pressure element and arms of the anchor assembly spread open. When deployed or opened, the arms of the anchor assembly are extended such that the end fitting is too wide to be pulled back out of the smaller-diameter tubing. Additionally, edges on the arms of the anchor assembly that engage with the inner cavity of the pressure element (e.g., the interior of the wide portion) can be tuned to pierce the cavity of the pressure element at specific pressure thresholds. For example, the anchor can be designed to pierce or puncture the cavity when a pressure level within the pressure element is some predetermined percentage (e.g. <NUM>%, <NUM>%, etc.) above a certification requirement, but still below a disengagement threshold. The edges may be flat, sharp, or blunt. Puncture of the cavity of the pressure vessel will provide pressure relief at the specific pressure threshold as designed, changing the failure mode from total end fitting disengagement to a slow leaking of gas through the pierced cavity and wall of the pressure element.

Another technique of retaining end fittings to pressure vessels is to use an adhesive, or another viscous or liquid substance, that cools or hardens between the cavity and tube of the stem of the end fitting to form an assembly with the stem of the end fitting fixed inside the tube or cavity of the pressure vessel using the cooled or hardened adhesive. The adhered parts provide a wide, solid base that is sized such that the adhered parts cannot be pushed out through the narrow portion of the tube of the pressure element. The wide portion of the pressure element will also help to distribute the stress acting on the end fitting and wide portion of the pressure element from the compressed gas.

Another technique of retaining end fittings to pressure vessel is to use a bulkhead assembly to secure the end fitting to a container or shell that surrounds the pressure elements. The use of the bulkhead assembly allows the container or shell to be a sturdy foundation to which the end fitting can be attached. The bulkhead assembly may include one or more collars and one or more nuts that either tighten or loosen the seal around the end fitting. A tether may also be included between a pressure vessel inside the container or shell and the end fitting outside of the container or shell to help keep the end fitting in place with respect to the container or shell.

The retention methods and techniques described herein can be used independently or together in order to improve end fitting retention for high-pressure, compressed-gas pressure vessels.

<FIG> is a perspective view of a pressure vessel assembly <NUM>. The pressure vessel assembly <NUM> includes end fittings <NUM> and pressure elements <NUM>. Each end fitting <NUM> includes a cap <NUM> and a stem <NUM>. The pressure vessel assembly <NUM> includes a shell <NUM> that is designed to capture gas that permeates from the pressure elements <NUM> and to protect the pressure elements <NUM>. On one of the pressure elements <NUM> that extend through the shell <NUM>, the end fittings <NUM> are shown. The end fittings <NUM> are designed to contain the pressurized gas within the pressure vessel assembly <NUM>. The end fittings <NUM> may also serve as connectors to valves, adaptors, couplings, or other interfaces to the pressure elements <NUM> within the pressure vessel assembly <NUM> for use in filling or emptying the pressure elements <NUM>.

<FIG> is a partial cross-sectional view of an end fitting <NUM> and a pressure element <NUM> for use with the pressure vessel assembly <NUM> of <FIG>. The pressure element <NUM> is surrounded by a reinforcement fiber <NUM>. The end fitting <NUM> connects with the pressure element <NUM> both through a cavity <NUM> defined within the pressure element <NUM> and with the reinforcement fiber <NUM> that surrounds the pressure element <NUM>. In other words, the pressure element <NUM> includes the cavity <NUM> and is covered by the reinforcement fiber <NUM>. The end fitting <NUM> includes a cap <NUM> and a stem <NUM>. Corrugation on a narrow portion <NUM> of the pressure element <NUM> is aligned with raised barbs <NUM> on the stem <NUM> and indents <NUM> on the cap <NUM>. Thus, when the cap <NUM> is crimped around the stem <NUM> and the narrow portion <NUM> of the pressure element <NUM> at the location of the corrugation of the narrow portion <NUM>, the cap <NUM> stretches axially, resulting in a tight fit between the pressure element <NUM>, the cap <NUM>, and the stem <NUM>. Crimping together the pressure element <NUM>, the cap <NUM> that is overlapping the narrow portion <NUM> of the pressure element <NUM>, and the stem <NUM> that is inserted into the cavity <NUM> of the pressure element <NUM> causes interference and friction between the pressure element <NUM>, the cap <NUM>, and the stem <NUM>. This crimped interface helps to hold the end fitting <NUM> in place both on an exterior of and within the cavity <NUM> of the pressure element <NUM>. However, this technique of retaining the end fitting <NUM> may be insufficient for some high-pressure applications.

<FIG> is a partial cross-sectional view of another end fitting <NUM> and another pressure element <NUM> for use with the pressure vessel assembly <NUM> of <FIG>. The end fitting <NUM> enters a cavity <NUM> of the pressure element <NUM>. The end fitting <NUM> includes a stem <NUM> with holes <NUM> disposed on the stem <NUM> along a portion of the stem <NUM> that reaches inside the cavity <NUM> of the pressure element <NUM>. The holes <NUM> are also disposed along a portion of the pressure element <NUM> that is crimped in a manner described in reference to <FIG>.

In the <FIG> example, if the end fitting <NUM> begins to disengage from the pressure element <NUM>, the stem <NUM> begins to move out of the cavity <NUM>. The holes <NUM> in the stem <NUM> will vent some of the pressurized gas that is forcing the stem <NUM> out of the cavity <NUM>. As the gas vents through the holes <NUM> of the stem <NUM>, there is less pressure exerted on the end fitting <NUM>. This reduction in pressure directly decreases the amount of force that the pressurized gas exerts onto the end fitting <NUM>. By reducing the pressure within the pressure element <NUM> below a predetermined pressure threshold, disengagement the end fitting <NUM> is either slowed or stopped, depending on the level of pressure reduction. For example, if the pressure element <NUM> is designed to store gas at <NUM>,<NUM> psi, (<NUM> bar), the end fitting <NUM> may begin to disengage from the pressure element <NUM> if stored gas reaches a level of <NUM>,<NUM> psi, (<NUM> bar), at which point, the holes <NUM> in the stem <NUM> will vent gas slowly, and pressure levels in the pressure element <NUM> will decrease, slowing or avoiding disengagement of the end fitting <NUM>.

<FIG> is a perspective view of an anchor <NUM> for use with a pressure element such as the pressure elements <NUM>, <NUM>, <NUM> of <FIG> in the pressure vessel assembly <NUM> of <FIG>. The anchor <NUM> is used in another technique of retaining an end fitting such as the end fittings <NUM>, <NUM>, or <NUM> of <FIG>. The anchor <NUM> includes a torsion spring <NUM>, a connector piece <NUM>, arms <NUM>, and a hole <NUM>. The anchor <NUM> is designed for attachment to a stem such as the stems <NUM>, <NUM>, <NUM> of <FIG> via the hole <NUM>, which can be threaded or otherwise configured for retention to the stem. The two arms <NUM> of the anchor <NUM> are held together by the torsion spring <NUM>. The torsion spring <NUM> can be formed with a relatively high spring constant to exert force against the arms <NUM>. The arms <NUM> of the anchor <NUM> can have flat edges that are rounded at the corners as shown in <FIG>. The edges of the arms <NUM> may also be designed to puncture a reinforcement fiber of a pressure element such as the pressure elements <NUM>, <NUM>, <NUM> of <FIG> at a pressure level or threshold that is below a disengagement pressure threshold for an end fitting such as the end fittings <NUM>, <NUM>, <NUM> of <FIG>. The arms <NUM> may thus enable a slower leak failure mode to be selected over an end fitting disengagement failure mode.

<FIG> is a cutaway, partial side view of an anchor <NUM> engaged with an end fitting <NUM> for use with a pressure element <NUM> that can be used in the pressure vessel assembly <NUM> of <FIG>. The anchor <NUM> is similar to the anchor <NUM> of <FIG>. The pressure element <NUM> includes a cavity <NUM> within a wider portion <NUM> and a narrow portion <NUM>. The end fitting <NUM> includes a stem <NUM> with threads <NUM> on the stem <NUM> that connect with the anchor <NUM> so that the anchor <NUM> is fixed atop the stem <NUM> and cannot move along the longitudinal axis of the stem <NUM>. To improve retention of the end fitting <NUM>, the stem <NUM> and anchor <NUM> are threaded into a cavity <NUM> of the pressure element <NUM>. The anchor <NUM> is fixed on the end of the stem <NUM> so that the anchor <NUM> cannot slide along the longitudinal axis of the stem <NUM> during insertion of the stem <NUM> or after the stem <NUM> is inserted into the cavity <NUM>. Arms <NUM> of the anchor <NUM> open up away from the narrow portion <NUM> of the pressure element <NUM> so that the arms <NUM> can close upon insertion of the anchor <NUM> and the stem <NUM> into the cavity <NUM> at the narrow portion <NUM> of the pressure element <NUM>. The arms <NUM> of the anchor <NUM> will expand to engage the pressure element <NUM> within the cavity <NUM> at the wide portion <NUM> of the pressure element <NUM>. The end fitting <NUM> and the pressure element <NUM> are then crimped together at the narrow portion <NUM> of the pressure element <NUM> to connect with the stem <NUM>. As the compressed gas within the pressure element <NUM> creates a force on the stem <NUM> axially outward from the pressure element <NUM>, the anchor <NUM> will create an opposite force at a location where the arms <NUM> interface with the pressure element <NUM> to keep the stem <NUM> in a fixed position.

When the stem <NUM> and the anchor <NUM> are coupled together, the stem <NUM> and the anchor <NUM> can be inserted into the cavity <NUM> of the pressure element <NUM>, and the arms <NUM> get pushed together by the narrow portion <NUM> of the pressure element <NUM> so that the arms <NUM> are generally parallel with the stem <NUM>. Once the anchor <NUM> reaches the wide portion <NUM> of the pressure element <NUM>, the spring of the anchor <NUM> pushes the arms <NUM> open to a predetermined angle based on the design of the spring. The angle may be about <NUM> degrees or more, about <NUM> degrees or more, about <NUM> degrees or more, or about <NUM> degrees or more. The angle may be about <NUM> degrees or less, about <NUM> degrees or less, about <NUM> degrees or less, about <NUM> degrees or less, or about <NUM> degrees or less. The anchor <NUM> is designed to open with a total angle measured between the arms <NUM> that is wider than the narrow portion <NUM> of the pressure element <NUM> so that the arms <NUM> prevent removal of the stem <NUM> from the cavity <NUM> of the pressure element <NUM>. Thus, the anchor <NUM> may change the failure mode from end fitting disengagement to slow leaking. This change in failure mode occurs because the anchor <NUM> punctures the pressure element <NUM> when the tensile force on the pressure element <NUM> reaches a predetermined pressure threshold. Therefore, at the pressure threshold of failure, the pressure element <NUM> leaks instead of the end fitting <NUM> disengaging from the pressure element <NUM>.

In some embodiments, designing the anchor <NUM> so that leaking of the pressure element <NUM> occurs above a predetermined pressure threshold to relieve pressure is optional in terms of the use of the anchor <NUM>. The anchor <NUM> can be designed so that the arms <NUM> fail through deformation of the spring or bodies of the arms <NUM> rather than causing a puncture or breaking apart of the anchor <NUM>. When the arms <NUM> are designed to bend instead of break, the arms <NUM> still cannot fit through the narrow portion <NUM> of the pressure element <NUM>, so slow leaking occurs in contrast to a broken anchor <NUM> which could slip out of the narrow portion <NUM> and allow a disengagement failure mode.

<FIG> is a cutaway, partial side view of another anchor <NUM> engaged with an end fitting <NUM> for use with a pressure element <NUM> similar to the pressure elements <NUM>, <NUM>, <NUM>, <NUM> of <FIG> and <FIG> for use in the pressure vessel assembly <NUM> of <FIG>. The anchor <NUM> engages with the pressure element <NUM> at a cavity <NUM> of a wide portion <NUM> and a narrow portion <NUM> of the pressure element <NUM>. The end fitting <NUM> includes a stem <NUM> that defines holes <NUM> similar to the holes <NUM> of <FIG>. The end fitting <NUM> includes a first ridge <NUM> and a second ridge <NUM> positioned along the end of the stem <NUM> that is inserted into the pressure element <NUM>. The first ridge <NUM> closest to the anchor <NUM> on the stem <NUM> is designed to be smaller, that is, to stand less proud from the stem <NUM>, than the second ridge <NUM> that is spaced from the first ridge <NUM> as shown in <FIG>.

As the end fitting <NUM> is pushed out of the cavity <NUM> due to excess pressure within the pressure element <NUM>, the anchor <NUM> pushes against the cavity <NUM> of the wide portion <NUM> of the pressure element <NUM>. The pushing of the anchor <NUM> causes a reaction force from the anchor <NUM> onto the first ridge <NUM>. The first ridge <NUM> is designed to fail, that is, to allow the anchor <NUM> to slide along the stem <NUM>, at a first pressure threshold. For example, the first pressure threshold can be <NUM>,<NUM> psi (<NUM> bar) if the pressure element <NUM> is designed to store gas up to <NUM>,<NUM> psi (<NUM> bar) or <NUM>,<NUM> psi (<NUM> bar) if the pressure element <NUM> is designed to store gas up to <NUM>,<NUM> psi (<NUM> bar). The stem <NUM> then slides partially outside of the narrow portion <NUM> of the pressure element <NUM> without moving the anchor <NUM> so that the anchor <NUM> is now pushing against the second ridge <NUM>. The second ridge <NUM> has a greater profile, overall size, and/or toughness than the first ridge <NUM> so that the second ridge <NUM> can withstand a greater force and will not fail until the pressure element <NUM> reaches a second, higher pressure threshold. For example, the second pressure threshold can be <NUM>,<NUM> psi (<NUM> bar) if the pressure element <NUM> is designed to store gas up to <NUM>,<NUM> psi (<NUM> bar) or <NUM>,<NUM> psi (<NUM> bar) if the pressure element <NUM> is designed to store gas up to <NUM>,<NUM> psi (<NUM> bar). Once the stem <NUM> moves outward from cavity <NUM>, the holes <NUM> become positioned outside of the cavity <NUM> and the narrow portion <NUM>, so the holes <NUM> can vent pressurized gas. The consequence is that less pressure generates less force against the anchor <NUM> and the end fitting <NUM> to prohibit disengagement or ejection of the end fitting <NUM>. The example pressure element <NUM> of <FIG> thus implements both the holes <NUM> and the anchor <NUM> to modify the failure mode and retain the end fitting <NUM>.

In some embodiments, the anchor <NUM> and the holes <NUM> provide a dual system of venting pressurized gas. The second ridge <NUM> of the stem <NUM> provides a stop to prevent the anchor <NUM> from sliding off the stem <NUM>. As described above, when the anchor <NUM> slides to the second ridge <NUM>, the holes <NUM> are pushed outside of the cavity <NUM> past the narrow portion <NUM> so that pressurized gas is vented. As the second ridge <NUM> holds the anchor <NUM> in a fixed position, the anchor <NUM> may then puncture the cavity <NUM> with the arms <NUM> of the anchor <NUM> so that both the punctures created by the arms <NUM> and the holes <NUM> are simultaneously venting pressurized gas.

<FIG> is a perspective view of a blunt anchor <NUM> and a sharp anchor <NUM> for use in place of the anchors <NUM>, <NUM> of <FIG>. The blunt anchor <NUM> has a rounded edge <NUM> that distributes stress on the cavity of the related pressure element. The rounded edge <NUM> of the blunt anchor <NUM> thus required a greater overall force to pierce the cavity to vent pressurized gas from the related pressure element than the sharp anchor <NUM>. The sharp anchor <NUM> pierces the cavity with a pointed edge <NUM> so that pressure element can vent pressurized gas at a lower predetermined pressure threshold. The sharp anchor <NUM> pierces a wide portion and inside the cavity of the related pressure element with the pointed edge <NUM> well before the end fitting that couples to the sharp anchor <NUM> can disengage from the related pressure element. Use of the sharp anchor <NUM> over the blunt anchor <NUM> depends on the pressure threshold at which the designer of the end fitting and/or the pressure element wants a controlled leak to occur.

<FIG> is a chart of retention capabilities and failure modes for the anchors <NUM>, <NUM>, <NUM>, <NUM>, <NUM> of <FIG> in terms of ejection or pull-out force. The chart shows the impact of different materials and designs for various anchors on the pressure threshold that dictates when partial or total ejection of the end fitting occurs based on pressure element failure vs. anchor failure. In other words, various design features of the anchors change the failure mode from ejection to piercing the pressure element. The blunt anchor <NUM> and the sharp anchor <NUM> of <FIG> are shown in the chart on the left side. The flattened anchor refers to a design with a larger, flat feature that distributes load, causing the stress on the pressure element to decrease. This material and design feature study shows that the anchor technique offers substantial assistance in end fitting retention when combined with another technique (such as holes in a stem of an end fitting) and is also effective in changing the failure mode from ejection to slower leak. The study also shows that the failure mode may be purposefully selected between the pressure element failure and anchor failure as desired, and these pressure threshold failure modes can be predicted based on the materials and design features chosen for the anchor.

<FIG> is a partially transparent side view of an adhesive-based retention method for an end fitting <NUM> similar to the end fittings <NUM>, <NUM>, <NUM>, <NUM>, <NUM> of <FIG> and <FIG>for use in a pressure element <NUM> that can be stored in the pressure vessel assembly <NUM> of <FIG>. The end fitting <NUM> is inserted into a cavity <NUM> to a wide portion <NUM> that is beyond the narrow portion <NUM> of the pressure element <NUM>. In other words, a stem <NUM> of the end fitting <NUM> extends into the cavity <NUM>. An adhesive plug <NUM> is deposited inside the cavity <NUM> at the wide portion <NUM> of the cavity <NUM> of the pressure element <NUM> at a location indicated by adhesive drops <NUM> being squeezed out of a tube <NUM> attached to a bottle <NUM> that supplies the adhesive. The adhesive drops <NUM> move through the tube <NUM> into the cavity <NUM> that surrounds the stem <NUM>. The adhesive drops <NUM> move through the tube <NUM> positioned in a center or passageway of the stem <NUM>. The pressure element <NUM> is positioned at an angle from vertical, that is, somewhat sideways, so when the adhesive drops <NUM> exit the tube <NUM>, gravity pushes the adhesive drops <NUM> down into the cavity <NUM>. While squeezing the bottle <NUM>, the pressure element <NUM> is rotated so that the adhesive plug <NUM> fills the cavity <NUM> evenly around the stem <NUM>. Once the adhesive plug <NUM> has been formed to an appropriate volume or level, the adhesive plug <NUM> is left to cool or harden and the tube <NUM> and the bottle <NUM> are removed from interface with the stem <NUM>.

<FIG> is a partially transparent side view of an end fitting <NUM> including an adhesive-based retention feature similar to that formed by the process described in <FIG>. The end fitting <NUM> extends into a pressure element <NUM> through a cavity <NUM> of both a wide portion <NUM> and a narrow portion <NUM> of the pressure element <NUM>. A stem <NUM> of the end fitting <NUM> includes rings or barbs <NUM> on an exterior surface that help create a form fit with the narrow portion <NUM> of the pressure element <NUM>. The barbs <NUM> help keep the stem <NUM>, and consequently the entire end fitting <NUM>, secured within the pressure element <NUM> via use of an adhesive plug <NUM>. Once the adhesive supplied in the manner described in <FIG> is hardened or cooled, the adhesive turns into the adhesive plug <NUM> having a solid form, and the adhesive plug <NUM> locks the stem <NUM> into a fixed position within the cavity <NUM> of the pressure element <NUM>. The adhesive plug <NUM> is sized so that it does not cover the hole extending axially through a center of the stem <NUM>, and gas still flows freely through the stem <NUM>.

In some embodiments, a sealer may be added on the end fitting <NUM> at a bottom of the adhesive plug <NUM> to stop any adhesive from leaking down between the stem <NUM> and the pressure element <NUM> before the adhesive has hardened. The adhesive plug <NUM> may be formed from nylon, epoxy, glue, cement, or any other material that forms a seal between the pressure element <NUM> and the stem <NUM>.

<FIG> is an exploded view of an end fitting <NUM> including the adhesive-based retention features described in <FIG> that is used to measure the strength of various adhesive-based retention features. The end fitting <NUM> including a stem <NUM> that is in a fixed position in an upper left of <FIG> with a pressure element <NUM> and adhesive plug <NUM> that extends between the pressure element <NUM> and the stem <NUM> being exploded along a common axis toward a lower right of <FIG>. The stem <NUM> has a sealed cap at a hole on the top of the stem <NUM> to contain pressurized gas used in the strength measurement. The end fitting <NUM> is attached with a steel stop <NUM> that is meant to mimic a reaction force generated by a reinforcement fiber, such as the reinforcement fiber <NUM> of <FIG>, used with the pressure elements <NUM> of the pressure vessel assembly <NUM>.

<FIG> is a perspective view showing a testing process to measure strength of an end fitting <NUM> using the adhesive-based retention feature described in <FIG>. The end fitting <NUM> has a <NUM> MPa load placed onto the end fitting <NUM> to correspond with a <NUM>,<NUM> psi failure pressure threshold achievable by a pressure element <NUM>. As the arrows show, the load is placed on an end of the pressure element <NUM>, a top of a stem <NUM>, a top of an adhesive plug <NUM>, and a top of steel stop <NUM>. This test process mimics forces experienced by the pressure element <NUM>, the end fitting <NUM>, and the adhesive plug <NUM> should the pressure element <NUM> be completely enclosed and contain <NUM>,<NUM> psi of compressed gas.

<FIG> is a graph showing retention capacity load sharing for different materials used in the adhesive-plug testing process described in <FIG>. The graph shows the capacity that each material has for load sharing or assisting the crimp to retain an end fitting such as the end fittings <NUM>, <NUM>, <NUM>, <NUM> of <FIG>. The plot point for steel is a reference that shows a lower retention capacity and yield strength than when Silicon Nitride is used. With a material such as Silicon Nitride, an adhesive plug such as the adhesive plugs <NUM>, <NUM>, <NUM> is able to provide a minimum safety factor of <NUM> when subjected to a <NUM> MPa load (about <NUM>,<NUM> psi). Under normal working conditions, the load pressure is <NUM> MPa (about <NUM>,<NUM> psi).

The minimum safety factor is a valuable indicator of successful improvement in end fitting retention since the target pressure, for example, a pressure of <NUM>,<NUM> psi, for the pressure element takes into account a degree of additional stress pressure as compared to a normal working pressure, for example, a pressure of <NUM>,<NUM> psi, for the relevant pressure element. Therefore, the Silicon Nitride exhibits good structural integrity at conditions that include significantly higher pressures than average conditions experienced by pressure vessel assemblies, like the pressure vessel assemblies <NUM> of <FIG>. Other adhesives, such as high or low strength epoxy, did not demonstrate as high a retention capacity or plug material yield strength.

As shown in <FIG>, yield strengths for the high strength and low strength epoxy were about <NUM> MPa for the high strength epoxy with <NUM>% retention capacity and about <NUM> MPa for the low strength epoxy at less than <NUM>% retention capacity. The graph of <FIG> thus shows that the use of an adhesive plug, particularly one formed from Silicon Nitride, provides improved end-fitting retention capacity that could be used to supplement, replace, or provide a more secure alternative to a standard crimped-shell design for end fitting retention. The graph also shows a distinction between end fitting retention and gas sealing aspects of a given retention design. That is, the adhesive plug can be used to provide retention of an end fitting while the crimped cap around the stem of the end fitting can be used to provide sealing for a pressure element.

<FIG> is a perspective view of a bulkhead <NUM> for use with the pressure vessel assembly <NUM> of <FIG>. The bulkhead <NUM> includes a collar <NUM> that can be tightened or loosened by adjusting a screw <NUM> holding ends of the collar <NUM> together. The screw <NUM> can be tightened or loosened to adjust a size of an opening in the collar <NUM>. The bulkhead <NUM> is shown as including a single screw <NUM>, but a bulkhead <NUM> may include one or more screws, two or more screws, three or more screws, or a plurality of screws so that the collar may be loosened or tightened appropriately.

<FIG> is a cutaway, partial side view of a bulkhead assembly <NUM> for use with the pressure vessel assembly <NUM> of <FIG>. The bulkhead assembly <NUM> surrounds an end fitting <NUM> and a pressure element <NUM>. The end fitting <NUM> includes caps <NUM>, <NUM> that both include platforms <NUM>. The end fitting <NUM> and the pressure element <NUM> connect through and are surrounded by a shell <NUM> that splits the caps <NUM>, <NUM> so that the end fitting includes a cap <NUM> that is external and a cap <NUM> that is internal. The caps <NUM>, <NUM> may contact each other, or the caps <NUM>, <NUM> may be separated by a space. The bulkhead assembly <NUM> includes a collar <NUM> that is internal and a collar <NUM> that is external. The collars <NUM>, <NUM> grip to and are held in place by the platforms <NUM> of the caps <NUM>, <NUM>. The collars <NUM>, <NUM> are separated at a vertical axis by the shell <NUM>. Both collars <NUM>, <NUM> surround the end fitting <NUM> and the pressure element <NUM>. The collar <NUM> that is internal connects with the cap <NUM> that is internal and presses against an inside of the shell <NUM>. The collar <NUM> that is external connects with the cap <NUM> that is external and presses against an outside of the shell <NUM>. The two collars <NUM>, <NUM> are tightened and forced together, which in turn applies pressure to the shell <NUM>, the pressure element <NUM>, and the end fitting <NUM> in between the collars <NUM>, <NUM>. As the pressure element <NUM> is pressurized and force is applied outward on the end fitting <NUM>, the bulkhead assembly <NUM> more evenly distributes this stress and holds the cap <NUM> that is external in place, which in turn holds the stem <NUM> in place.

The bulkhead assembly <NUM> may include a tether <NUM> for retaining the end fitting <NUM>. The tether <NUM> may connect the end fitting <NUM> and the shell <NUM> or the end fitting <NUM> and the pressure element <NUM> inside of the shell <NUM>. In the <FIG> example, the tether <NUM> is wrapped around and tied to the stem <NUM>, pushed through the hole in the shell <NUM> along the collar <NUM>, and tied to a curved portion <NUM> of the pressure element <NUM> within an interior of the shell <NUM>. This technique using the tether <NUM> increases the likelihood of the end fitting <NUM> being retained regardless of the failure mode and can be used in combination with other retention techniques to provide redundancy.

<FIG> is a cutaway, partial side view of another bulkhead assembly <NUM> for use with the pressure vessel assembly <NUM> of <FIG>. The bulkhead assembly <NUM> connects an end fitting <NUM> and a pressure element <NUM>. The end fitting <NUM> includes caps <NUM>, <NUM>. The caps <NUM>, <NUM> may contact each other or may be separated by a space. The end fitting <NUM> includes a stem <NUM> that is inserted through a shell <NUM> to connect with the pressure element <NUM>. A collar <NUM> that is internal is screwed onto the cap <NUM> that is internal, and a collar <NUM> that is external is screwed onto the cap <NUM> that is external. The collars <NUM>, <NUM> are separated by a vertical axis of the shell <NUM>. The collars <NUM>, <NUM> screw together so that the collars <NUM>, <NUM> can squeeze around the shell <NUM> and apply a pressure to the end fitting <NUM>, the pressure element <NUM>, and the shell <NUM>. The bulkhead assembly <NUM> may include a tether <NUM> for retaining the end fitting <NUM>. The tether <NUM> may connect the end fitting <NUM> and the shell <NUM> or the end fitting <NUM> and the pressure element <NUM> inside of the shell <NUM>. In the <FIG> example, the tether <NUM> is wrapped around and tied to the stem <NUM>, pushed through the hole in the shell <NUM> along the collar <NUM>, and tied to a curved portion <NUM> of the pressure element <NUM> within an interior of the shell <NUM>. This technique using the tether <NUM> increases the likelihood of the end fitting <NUM> being retained regardless of the failure mode and can be used in combination with other retention techniques to provide redundancy.

In some embodiments, the caps <NUM>, <NUM> and the collars <NUM>, <NUM> may be tightened down with a wrench or any other means capable of tightening a threaded cylinder. The shell <NUM> may be reinforced to increase the pressure threshold capable before disengagement of the end fitting <NUM> from the pressure element <NUM>. The collars <NUM>, <NUM>, <NUM>, <NUM>, that are squeezed together may include nuts, adjustable rings, bolts, or any combination of tightening on tensioning mechanisms. The collars <NUM>, <NUM> may be threaded to match the caps <NUM>, <NUM>.

<FIG> is a cutaway, side view of another bulkhead assembly <NUM> for use with the pressure vessel assembly <NUM> of <FIG>. The bulkhead assembly <NUM> may be similar to the bulkhead assemblies <NUM>, <NUM> of <FIG>. The bulkhead assembly <NUM> includes a pressure element <NUM>, which may be comprised of a gas containing liner and a reinforcement layer, attached to an end fitting <NUM> so that the pressure element <NUM> has a bendable and/or extendable connection between other pressure elements (not shown) and outside components. The pressure element <NUM> has a wide portion <NUM> that is connectable to a transition portion <NUM> and has a narrow portion <NUM> that is interface-able with a stem <NUM> that is connectable to a gas source (not shown). As the stem <NUM> extends from outside of a shell <NUM> and extends well into the pressure element <NUM> and/or the wide portion <NUM> of the pressure element <NUM>, a cap <NUM> is used to surround and/or squeeze together the stem <NUM> and the narrow portion <NUM> so that the stem <NUM> is radially and fluidly secured by the cap <NUM>. To keep the stem <NUM> axially secure inside of the pressure element <NUM>, corrugations <NUM> on an internal surface of the cap <NUM> are interface-able or locked with barbs <NUM> on an external surface of the stem <NUM>. The corrugations <NUM> and the barbs <NUM> are useful to prevent pushing or pulling of the stem <NUM> in an axial direction, when the cap <NUM> is squeezed and/or secured over the stem <NUM>.

Since the cap <NUM> is positioned on the inside of the of shell <NUM> relative to outside of the bulkhead assembly <NUM>, collars <NUM>, <NUM> are used to provide a mechanism for preventing both axial and radial motion of the stem <NUM>, pressure element <NUM>, and cap <NUM> relative to the shell <NUM>. The collars <NUM>, <NUM> and the stem <NUM> have threaded portions <NUM> that can be screwably secured when the stem <NUM> is inserted into the narrow portion <NUM> of the pressure element <NUM>. The stem <NUM> is shown as having multiple threaded portions <NUM>, spaced apart axially along the stem <NUM>, that are sized to account for various thicknesses of the shell <NUM>, use of the collars <NUM>, <NUM>, and interface with the gas source (not shown). The shell <NUM> may further include threaded portions (not shown) for an additional feature to secure the stem <NUM>.

Before the bulkhead assembly <NUM> is fully assembled, the cap <NUM> is squeezed and/or secured around the narrow portion <NUM> and the stem <NUM>, and the collars <NUM>, <NUM> are threaded with the stem <NUM> so that the cap <NUM> is properly positioned for the crimping operation. Gases are flow-able between the pressure element <NUM> and an outside environment through a channel <NUM> of the stem <NUM>. In this configuration, the gases should not be flowing or leaking at a space between the external surface of the stem <NUM> and the internal surface of the narrow portion <NUM>. Further, as the collars <NUM>, <NUM> and the cap <NUM> are wrapped or squeezed around an opening <NUM> of the shell <NUM>, gases are prevented from flowing and/or leaking out the shell <NUM> at the opening <NUM>.

Claim 1:
A pressure vessel system, comprising:
a pressure element (<NUM>) configured to store compressed gas;
a shell (<NUM>) configured to enclose the pressure element (<NUM>) and capture the compressed gas that permeates from the pressure element (<NUM>);
an end fitting (<NUM>) extending into a cavity of the pressure element (<NUM>) and from the pressure element (<NUM>) through the shell (<NUM>), the end fitting (<NUM>) comprising:
a stem (<NUM>) that extends out from the shell (<NUM>) in one direction and into the cavity of the pressure element (<NUM>) in an opposite direction; and
a cap (<NUM>, <NUM>) that surrounds the pressure element (<NUM>) and the stem (<NUM>) at a location external to the pressure element (<NUM>); and
a retention component configured to sustain engagement of the end fitting (<NUM>) with at least one of the pressure element (<NUM>) or the shell (<NUM>) below a predetermined pressure threshold;
wherein the retention component comprises:
a tether (<NUM>) with a first end coupled to the stem (<NUM>) at a location external to the shell (<NUM>) and a second end coupled to a curved portion (<NUM>) of another pressure element (<NUM>) interior to the shell (<NUM>).