Abstract:
Described herein are systems and methods for cryogenic fluid delivery. The systems may include a pressure vessel containing a cryogenic fluid formed of liquid and vapor that is connected to a use device via a withdrawal line. The withdrawal line connects to the cryogenic fluid in the pressure vessel via two routes, a liquid tube and a vapor line. The vapor line may include a back-pressure regulator that opens the vapor line depending on pressure in the system. The withdrawal line may include a pressure relief valve that exerts pressure on the liquid tube. A bypass line may connect the withdrawal line to the liquid tube. The bypass line has a check valve that permits free flow of cryogen from the withdrawal line to the liquid tube via the bypass line while prohibiting cryogen flow from the pressure vessel through the bypass line. The methods employ the systems described herein.

Description:
BACKGROUND 
     Liquid Natural Gas (LNG) vehicle pressure vessels are widely used in heavy duty trucking operations. U.S. Pat. No. 5,421,161 describes an improved cryogenic fuel tank system. The system is particularly useful in horizontal cryogenic tanks (i.e. pressure vessels), such as those containing low-density fluids like LNG. However, while the system of the &#39;161 patent works quite well for reducing pressure inside a pressure vessel through an economizer circuit, it actually limits the pressure vessel&#39;s ability to build pressure in mobile applications because it limits the rate of backflow of product to the vessel. 
     In view of the foregoing, there is a need for an improved cryogenic fuel pressure vessel system that is particularly suited for horizontal fuel pressure vessels. 
     SUMMARY 
     Described herein are systems and methods for delivering cryogenic fluid from a pressure vessel to a use device through a combination of a liquid tube, a withdrawal line, and a vapor line. In some embodiments, the system may include a pressure vessel containing a cryogen formed of a liquid and a vapor located above the liquid, a withdrawal line configured to deliver the cryogen to a use device, and a liquid tube extending into the liquid and connecting the liquid with the withdrawal line. In such embodiments, a first pressure in the pressure vessel forces liquid into the withdrawal line via the liquid tube when the withdrawal line is open. The system may further include a vapor line, extending into the vapor and connecting the vapor with the withdrawal line, and a back-pressure regulator coupled to the vapor line. In such embodiments, the back-pressure regulator opens the vapor line when a second pressure in the system exceeds a predetermined value so as to permit vapor to pass through the vapor line to the withdrawal line. The system may further include a pressure relief valve coupled to the withdrawal line, in which the pressure relief valve exerts a back pressure on the liquid tube such that a path of least resistance for cryogen out of the pressure vessel into the withdrawal line is through the vapor line whenever the pressure regulator is open. The system may also include a bypass line, connecting the withdrawal line to the liquid tube, and a check valve coupled to the bypass line, in which the check valve is configured to permit free flow of cryogen from the withdrawal line to the liquid tube and the pressure vessel via the bypass line, and in which the check valve is further configured to prohibit cryogen to flow from the pressure vessel to the withdrawal line via the bypass line. 
     In some embodiments, the check valve and pressure relief valve are contained in a single housing. In some such embodiments, the single housing includes the bypass line. Some embodiments may include a pressure vessel in which the pressure vessel is thermally insulated. Embodiments may include those in which the use device is a vehicle engine. In some embodiments, the pressure vessel may be mounted on a vehicle. Some embodiments may include those in which the pressure vessel is a horizontal pressure vessel. Some embodiments may include a pressure relief valve that exerts a back pressure of about 1 to 3 psi. In some embodiments, the withdrawal line includes a vaporizer for converting liquid cryogen to gas. Embodiments may also include those in which the cryogen is liquid natural gas. 
     Some embodiments may include a method for cryogenic fluid delivery to a gas use device in a system that includes a pressure vessel containing a cryogenic fluid formed of a liquid and a vapor. In such embodiments, the method may include permitting the cryogenic fluid to flow from the pressure vessel towards the gas use device via a withdrawal line. Further in such embodiments, the cryogenic fluid can flow from the pressure vessel to the withdrawal line through either a vapor line having a back-pressure regulator or through a liquid tube in which a first pressure in the pressure vessel forces liquid into the withdrawal line via the liquid tube when the withdrawal line is open and in which the regulator opens the vapor line when a second pressure in the system exceeds a predetermined value so as to permit vapor to pass through the vapor line to the withdrawal line. The method may further include exerting a back pressure on the liquid tube such that a path of least resistance for cryogen out of the pressure vessel into the withdrawal line is through the vapor line whenever the regulator is open. Additionally, the method may include permitting fluid in the withdrawal line to flow back into the pressure vessel via a bypass line connecting the withdrawal line to the liquid tube. In such embodiments, a check valve may be coupled to the bypass line, and the check valve is configured to permit free flow of cryogenic fluid from the withdrawal line to the liquid tube and the pressure vessel via the bypass line when a third pressure in the withdrawal line exceeds the first pressure in the pressure vessel. 
     Some embodiments may also include a method in which the check valve and pressure relief valve are contained in a single housing. In some such embodiments, the single housing may also include the bypass line. In some embodiments of the method, the use device may be a vehicle engine. Some embodiments may further include a pressure vessel in which the pressure vessel is mounted on a vehicle. Embodiments of the method may also include those in which the pressure vessel is a horizontal pressure vessel. In some embodiments, the cryogenic fuel delivery system further includes a control valve located along the withdrawal line. Some embodiments may include those in which the use device includes a throttle that varies a demand for cryogen by the use device. Embodiments may further include those in which the cryogen is liquid natural gas (LNG). In some embodiments, the method further includes allowing cryogenic vapor in the withdrawal tube to flow back into the pressure vessel via the vapor line. Some embodiments may include those in which the cryogenic fluid delivery system further includes a vaporizer for converting cryogenic liquid to vapor, the vaporizer located along the withdrawal line, and further in which the vaporizer imparts heat to the cryogenic fluid in the withdrawal line and allows the cryogenic fluid to expand. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary system diagram of a cryogenic fluid storage and delivery system with a vertical pressure vessel; 
         FIG. 2  shows an exemplary system diagram that includes a forwarding biasing valve and an orifice; 
         FIG. 3  shows an exemplary system that includes an integrated forward biasing valve and a check valve with reverse free-flow capabilities; 
         FIG. 4  shows an exemplary integrated forward biasing valve with reverse free-flow capabilities; 
         FIG. 5  shows a sectional view of an exemplary forward biasing valve with reverse free-flow capabilities. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed is a cryogenic fluid storage and delivery system. The system is primarily described herein in the context of being used for a horizontal liquid natural gas (LNG) pressure vessel that provides vehicular fuel to natural gas engines. However, it should be appreciated that the system can be used with any of a variety of mobile horizontal delivery tanks such as liquid nitrogen pressure vessels used for in-transit refrigeration. Moreover, although the disclosure is primarily described in terms of supplying fuel to an engine, it should be appreciated that the disclosed system may be configured for use with any application that uses cryogenic fluids. 
     By way of background,  FIG. 1  shows an example of a conventional cryogenic storage and delivery system that delivers a cryogenic fluid to a device. The system includes a pressure vessel  105 , such as a large, insulated container that may vary in size. In this document, references to fuel tanks, storage tanks, containers, or the like may be considered to refer to pressure vessels. In example, the pressure vessel  105  is vertically oriented, such as about 1 to 1.5 meters (approximately 3 to 5 feet) in height. The pressure vessel  105  contains a cryogenic liquid  110 . A layer of vapor  115  is located in the pressure vessel  105  above the liquid  110  in the pressure vessel  105 . The vapor  115  is typically present as a result of the tank not being 100% full of liquid to allow for liquid expansion due to heat influx. 
     With reference still to  FIG. 1 , a liquid tube  120  extends into the pressure vessel  105  with a bottom end of the liquid tube  120  immersed in the cryogenic fluid  110 . The liquid tube  120  communicates with a withdrawal line  125 , which connects to a gas use device  150 . A vaporizer  130  is positioned along the withdrawal line  125  for heating and vaporizing the liquid  110  prior to the liquid being delivered through a control valve  160  to the gas use device  150 . It should be understood that in this document, the term vaporizer is used to include a heat exchanger. 
     A vapor line  140  also communicates with the pressure vessel  105 . A bottom end of the vapor line  140  is positioned within the layer of vapor  115  above the cryogenic liquid  110 . The vapor line  140  is part of an economizer circuit  135  that controls the pressure vessel&#39;s pressure. The economizer circuit  135  includes a back-pressure regulator  145  that senses the pressure within the pressure vessel and is configured to open at a predetermined pressure threshold. The vapor line  140  communicates with the withdrawal line  125  thereby providing a pathway for the vapor  115  to flow from the pressure vessel  105  to the withdrawal line  125  and ultimately to the gas use device  150 . The withdrawal line  125  also allows for vapor or liquid to flow back to the pressure vessel  105  when control valve  160  is closed. To efficiently control the pressure of the pressure vessel  105 , it is generally desirable to release the vapor  115  from the pressure vessel  105  during periods of use. By allowing vapor to flow into the withdrawal line, the economizer circuit  135  allows for rapid pressure reduction when the regulator  145  is open. It should be appreciated that releasing a given mass of the vapor  115  from the pressure vessel  105  results in a relieving of pressure at a much greater rate than releasing the same given mass of the liquid  110  from the tank. 
     The system of  FIG. 1  works as follows. The cryogenic liquid  110  exits the pressure vessel  105  by passing upward through the liquid tube  120  into the withdrawal line  125 . The vaporizer  130  adds heat to the liquid  110  to vaporize the liquid  110  for delivery to the gas use device  150  in gaseous form. The economizer circuit  135  provides a mechanism for releasing the vapor  115  from the pressure vessel  105 , which also results in a release of pressure from the tank. In this regard, the regulator  145  opens to permit the vapor  115  to release from the pressure vessel  105  via the vapor line  140  whenever the pressure in the pressure vessel  105  exceeds the pressure level set at the regulator  145 . For pressure vessels that are positioned in a vertical orientation, the vapor line  140  of the economizer circuit  135  provides the preferred path over the liquid tube  120  for release of fluid from the pressure vessel  105  whenever the regulator  145  is open. This is because lifting liquid up the long, vertical length, or height, of the liquid tube  120  provides a pressure head that resists flow of the liquid  110  out of the pressure vessel  105  via the liquid tube  120 . In other words, the economizer circuit  135  provides the path of least resistance for flow of fluid out of the pressure vessel  105 . 
     A drawback in the system of  FIG. 1  arises as the vertical length of the liquid tube  120  decreases, such as in horizontal tanks where the liquid tube  120  has a much smaller height than in vertical tanks. Since the pressure head is lower for liquid tubes with shorter vertical lengths, the flow resistance provided by that the pressure head becomes negligible. As a result, the vapor line  140  may not provide the path of least resistance for flow of fluid out of the pressure vessel. In such a situation, when a demand for product is made and the regulator  145  is open, the liquid  110  may be delivered out of the pressure vessel  105  via the liquid tube  120  in place of or simultaneously with the vapor  115  being delivered out the pressure vessel  105  via the vapor line  140 . In addition, a high flow demand for product has the same drawback as a short liquid tube discussed above. High flow may cause a pressure drop in the line larger than the difference in head pressure. Under such circumstances, both liquid and vapor flow simultaneously from the pressure vessel  105 , and the pressure in the pressure vessel  105  cannot be quickly or effectively lowered, as in situations when vapor predominates the flow out of the pressure vessel  105 . 
     Pressure head varies with liquid density such that a heavier liquid such as argon generates four times the head pressure of LNG at the same liquid height. Thus, the aforementioned drawbacks are more acute for light cryogens such as LNG. In a typical 3 to 5 foot tall vertical tank filled with LNG, the pressure head created in liquid tube is 1 to 2 psi Because of the head pressure in the liquid tube  120 , the resistance to flow in the vapor line  140  is 1 to 2 psi lower than the resistance to flow in the liquid tube  120  such that the economizer circuit  135  will initially deliver gas to the gas use device thereby lowering the pressure in the tank until the pressure falls below the value set at the regulator at which time the regulator will close and liquid will be delivered via the liquid tube  120 . 
       FIG. 2  shows an example of a partial solution to the above-mentioned drawback where the short vertical length of the liquid tube does not provide a sufficient level of pressure head to resist liquid fluid flow out of the liquid tube. As mentioned, this drawback may be present in horizontal tanks where the liquid tube has a much shorter height than in vertical tanks. The system of  FIG. 2  is described in U.S. Pat. No. 5,421,161, which is incorporated herein by reference in its entirety. Horizontal pressure vessels are commonly used as fuel tanks on vehicles where the tank is mounted to the underside of the vehicle and the tank stores LNG that fuels the vehicle&#39;s engine. 
     With reference still to  FIG. 2 , the pressure vessel  205  is horizontal such that it is significantly less tall than it is long. In an example, the tank has a total height of only approximately 10 to 20 inches, significantly less than the 3 to 5 feet of some vertical pressure vessels. The pressure vessel  205  may be, for example, an insulated, double-walled structure with a vacuum layer between the walls to prevent heat from the surroundings from reaching the cryogenic fluid. As in the system of  FIG. 1 , the pressure vessel  205  contains a cryogenic liquid  210  and a layer of vapor  215  above the cryogenic fluid. A liquid tube  220  extends into the cryogenic liquid  210  and communicates with a withdrawal line  225  that connects to a gas use device  150 . A vaporizer  230  is positioned along the withdrawal line  225  for vaporizing the fluid before it is delivered to the gas use device  150 . A control valve  260  is also positioned along the withdrawal line  225 . Cryogenic liquid  210  or vapor  215  is provided to the withdrawal line  225  while the control valve  260  is open. When the control valve  260  is closed, cryogenic liquid or vapor may return to the pressure vessel through orifice  255 . 
     As shown in  FIG. 2 , an economizer circuit  235  provides a pathway for the vapor  215  to flow out of the pressure vessel  205 . As in the system of  FIG. 1 , the economizer circuit  235  includes a vapor line  240  coupled to a back-pressure regulator  245 . The regulator  245  opens at a predetermined pressure to permit release of the vapor  215  from the pressure vessel  205 , as described above with respect to  FIG. 1 . The regulator  245  is reversed from the regulator  145  shown in the system of  FIG. 1  such that the regulator  245  senses the pressure in the vapor line  240  rather than sensing pressure in the pressure vessel  205 . 
     With reference still to  FIG. 2 , the withdrawal line  225  includes a relief valve  250  located downstream of the liquid tube  220  and upstream of the vaporizer  230 . Since there is no longer a return flow path from the withdrawal line to the tank, the withdrawal line  225  also includes an orifice  255  that bypasses the relief valve  250 . The relief valve  250  and orifice  255  collectively enable the system of  FIG. 2  to work efficiently, as will be described in detail further below. 
     The system of  FIG. 2  works similar to the system described with respect to  FIG. 1 . However, the relief valve  250  is configured to provide a predetermined level of back pressure in the liquid tube  220 . It should be appreciated that any device configured to provide a level of back pressure may be used, such as, for example, a weight or an automatic valve. (Accordingly, this disclosure is not limited to the use of a pressure relief valve.) The pressure relief valve  250  thus ensures that the liquid tube  220  has a back pressure that is greater than the back pressure in the economizer circuit  235 . When the regulator  245  is open, the vapor  215  will preferentially flow out of the pressure vessel  205  to the use device  150  via the economizer circuit  235 , which provides the path of least resistance out of the pressure vessel  205  as a result of the back pressure in the liquid tube  220  provided by the relief valve  250 . Upon closing of the regulator  245 , the liquid  210  flows out of the pressure vessel  205  via the liquid tube  220  through the pressure relief valve  250  to the use device  150 . 
     Since cryogenic fluid remains in the withdrawal line  225  when the control valve  260  closes, a return path to the tank  205  must be provided. There are two pathways to accommodate return flow to the tank: the economizer circuit  235  and the orifice  255 . The primary return pathway is through orifice  255 . The orifice  255  provides a free flow pathway for fluid from the withdrawal line  225  back to the pressure vessel  205  via the liquid tube  220 . Since the orifice has to be small in both diameter and flow rate so as not to short circuit the function of relief valve  250 , an alternative return path is also provided. In the economizer circuit  235 , the regulator  245  senses the pressure in the portion of the vapor line  240  that connects to the withdrawal line  225 . The regulator  245  allows return flow from the withdrawal line  225  to the tank  205  when the pressure in the withdrawal line  225  exceeds its set point. This happens when the relatively small return flow rate through the orifice  255  is exceeded by the rate of vapor generation in the vaporizer (i.e. heat exchanger)  230  and withdrawal line  225 . This can happen when a large liquid flow to the use device is interrupted by the control valve  260 . For example, where the system is a vehicle system, the control valve  260  may comprise a throttle valve and a throttle. Cryogenic fluid remaining in the withdrawal line  225  during transient throttle conditions such as when the throttle closes or reduces during coasting of the vehicle will cause there to be more liquid in the vaporizer  230  and withdrawal line  225  than the engine demands. Over time, the pressure within the withdrawal line  225  and vaporizer  230  may rise, such as due to vaporization of liquid remaining in the line or due to transient throttle conditions. If the rate of pressure rise exceeds the rate of pressure decay provided by return flow through the orifice  255 , the line pressure will rise until it reaches the regulator set pressure, causing it to open, providing a large return flow path to the tank  205  through the regulator  245 . Since the tank  205  normally operates at the set pressure of the regulator  245 , the regulator will normally cycle open with every power reduction of the vehicle providing a constantly large and fast path for return flow. 
     The back flow of fluid from the withdrawal line  225  to the pressure vessel  205  via the regulator  245  and orifice  255  serves some useful and important purposes. For example, the backflow of fluid into the pressure vessel  205  serves to relieve pressure in the withdrawal line  225 . In addition, the back flow of fluid from the withdrawal line  225  to the pressure vessel  205  also carries heat back with it to the liquid  210  in the pressure vessel  205 . The return heat is absorbed by the liquid, which helps to maintain pressure in the pressure vessel  205 . This pressure maintenance pathway may be highly desirable in LNG vehicles. With the proliferation of LNG vehicles, fuel stations, and engines, it has becoming increasingly common, though undesirable, to fuel a vehicle with LNG that is at a pressure lower than the pressure desired by the engine. 
     In operation the normal heat leak through the tank insulation, via mechanical agitation of the liquid in the tank, and the return heat flow through the orifice and regulator adds sufficient heat to maintain pressure within the pressure vessel at its operating pressure when correctly fuelled. However, if the tank&#39;s pressure is below its normal operating pressure from mis-fuelling, it requires additional heat to build the pressure in the tank back up to its normal operating pressure. Unfortunately, the system of  FIG. 2  has a drawback in that in order for the orifice  255  to allow the relief valve  250  to effectively bias the pressure in the liquid tube  220 , it is necessarily too small to provide a sufficient amount of backflow of heated fluid to the pressure vessel that would generate the required pressure increase within the required amount of time. 
     The regulator  245  setting determines the tank&#39;s normal operating pressure and is set to match the minimum pressure desired by the engine. When fuelling a tank, the fuel is normally delivered at or above this minimum pressure to ensure normal engine operation. However, if the tank is fuelled at a pressure below its normal operating pressure, it will cause operational problems. For example, if a tank with a regulator  245  setting of 100 psig is fuelled with fuel at 70 psig, the vehicle will initially run poorly because its pressure is 30 psi below the pressure required for normal operation. The vehicle&#39;s acceleration will be sluggish; it may run quite roughly and may not be able to develop full power since the tank&#39;s pressure is insufficient to deliver the fuel demand of the engine. To get the tank&#39;s operating pressure back to normal, a large heat flow to the liquid is required to cause its pressure to rise. However, since LNG tanks are designed to keep heat out, the natural pressure rise from 70 psig to 100 psig may take several days, which is undesirable. Additionally, the return flow of heat from the vaporizer  230  to the pressure vessel through the economizer circuit  235  will not occur until the withdrawal line  225  pressure has built up from 70 psig to the 100 psig setting of the regulator  245 . Since much of this return flow is caused by transient throttle operation, the time it takes to build line pressure from 70 to 100 psi normally exceeds the time interval between the driver getting back onto the throttle, so much of the excess heat and pressure is simply delivered to the engine instead of the tank. 
       FIG. 3  shows a system that is configured to maintain functionality and safety features of the system of  FIG. 2 , while allowing free flow of fluid back into the pressure vessel  205 . The system of  FIG. 3  overcomes a problem with slow pressure rise that occurs with tanks fuelled below the proper operating pressure. With reference to  FIG. 3 , the system is configured in a similar manner as the system of  FIG. 2 . Thus, like reference numerals between  FIGS. 2 and 3  refer to like components and the description of  FIG. 2  applies to the system of  FIG. 3 . 
     The system of  FIG. 3  includes a check valve  305  in place of the orifice  255  of the system of  FIG. 2 . In the forward flow direction (i.e., the direction from the pressure vessel  205  toward the gas use device  150 ), the check valve  305  is shut, which allows the relief valve  250  to bias the flow out of the vapor line  240  just as in the system of  FIG. 2 . However, the check valve  305  provides an unimpeded back flow path for liquid and vapor to return from the vaporizer  230  toward the pressure vessel  205 . Since the check valve permits a free flow of vapor and liquid from the withdrawal line  225  to the pressure vessel  205 , the backflow of heat to the pressure vessel is always available to assist the pressure vessel  205  in maintaining or building pressure, independent of the regulator  245  setting. This allows tanks (i.e. pressure vessels) that are mis-fuelled with low pressure fuel to quickly rebuild pressure and resume normal operation. 
       FIG. 4  shows an exemplary structural configuration of the relief valve  250  and check valve  305 , which may both be provided in a single housing  450  that is positioned at a juncture between the liquid tube  220  and the withdrawal line  225 , ahead of the vapor line  240  juncture. The housing  450  has a first port  455  for fluid to flow from the liquid tube  220  into the housing  450 . The housing  450  also has a second port  460  and outlet holes  465  for fluid to flow from the housing  450  into the withdrawal line  225 , or from the withdrawal line  225  into the housing  450  in the case of backflow. It should be appreciated that the configuration shown in  FIG. 4  is an example and that other configurations may be used. 
       FIG. 5  shows a cross-sectional view of the cylindrical housing  450  of  FIG. 4  and provides details of an exemplary mechanism for the check valve  305  and the relief valve  250  ( FIG. 3 ). The housing  450  defines an internal lumen  505  positioned within and along the length of the housing. The housing also includes a retainer  510 , a spring  515 , and outlet holes  465  and  460  that provide a pathway for fluid to flow out of or into the lumen  505 . Inside the lumen  505  is a moveable check valve  520  that is adjacent to the outlet holes  465  and the spring  515  in a default state. The moveable check valve  520  includes a ball  535  and a retainer  540  to keep the ball  535  in place. In the default state, the moveable check valve  520  is positioned against a seat  550 , so that it blocks flow from liquid tube  220  to withdrawal line  225 . 
     When the cryogenic liquid  210  ( FIG. 3 ) flows from the pressure vessel  205  ( FIG. 3 ) to the use device  150  ( FIG. 3 ), the liquid enters the lumen  505  from the liquid tube  220  through port  455 . The liquid passes the retainer  540  and pushes the ball  535  toward and into the seat  545  of the moveable check valve  520  blocking passage  525 . The spring  515  force now acts against the pressure of the liquid through the closed check valve  520  providing the necessary back pressure for the proper function of the regulator  245 . Once the pressure of the liquid acting against the check valve  520  exceeds the spring force, it moves the moveable check valve  520  against the spring  515  towards the retainer  510 . In this manner, the movable check valve  520  moves out of engagement with the seat  550  so that it no longer blocks flow from the liquid tube  220 , allowing liquid to flow through the outlet holes  465  into the withdrawal line  225 . 
     The mechanism shown in  FIG. 5  allows for quick and relatively unimpeded flow of fluid from withdrawal line  225  ( FIG. 3 ) to the pressure vessel  205  ( FIG. 3 ) relative to the system of  FIG. 2 , which requires the liquid to flow back through the small orifice  255  or build sufficient pressure to open regulator  245 . When the control valve  260  ( FIG. 3 ) closes (or throttle is rapidly reduced), the pressure in the withdrawal line  225  will exceed the pressure in the liquid tube  220 . The retainer  510  includes an opening  460  that allows flow through the retainer  510 , past the spring  515 , through the moveable check valve  520 , past the ball  535  and retainer  540 , and out the lumen  505  to the liquid tube  220  ( FIG. 3 ). Since the pressure exerted on the movable check valve is now less than the spring force, the moveable check valve  520  moves back to the default state shown in  FIG. 5  such that the moveable check valve  520  engages the seat  550 . The fluid from the withdrawal line  225  flows through openings  460  &amp;  525  and pushes the ball  535  off the seat  545  to provide an opening for fluid to flow freely around the ball. The retainer  540  keeps the ball  535  in place and allows for fluid flow around the ball  535 , through the lumen  505 , out of first port  455 , into the liquid tube  220  ( FIG. 3 ), and into the pressure vessel  205 . 
     As the diameter of the lumen  505  is much greater than the orifice  255  ( FIG. 2 ), the return of fluid through the mechanism shown in  FIG. 5  is quicker and allows for more rapid transfer of heat from outside the pressure vessel  205  ( FIG. 3 ) to the cryogenic liquid  210  ( FIG. 3 ). Thus, the cryogenic fluid storage and delivery system has the ability to build the pressure within the pressure vessel to a desired level and then maintain that pressure with less variation. In a cryogenic fluid storage and delivery system that is used as a fuel providing system in a vehicle, this maintenance of pressure within the pressure vessel enables the vehicle to operate at proper engine efficiency and power. 
     The specifications of the mechanism shown in  FIG. 5  may vary. Below are some exemplary mechanism specifications. In some embodiments, the mechanism shown in  FIG. 5  is configured such that the force exerted by the spring  515  on the moveable check valve  520  is a set value equal to 1 to 3 psi (approximately 6.9 to 20.7 kPa). In some embodiments, the force exerted by the spring  515  is variable and may be changed to suit various requirements. 
     The mechanism shown in  FIG. 5  is shown horizontally placed, such that the long axis of the housing  450  is parallel to the ground. In some embodiments, the housing  450  is horizontally placed, and the pressure in the withdrawal line  225  ( FIG. 3 ) need only be slightly more than the pressure in the liquid tube  220  ( FIG. 3 ) for fluid to flow towards the pressure vessel  205  ( FIG. 3 ) from the withdrawal line  225  ( FIG. 3 ). In some embodiments, the mechanism is placed such that the long axis of the housing  450  is not horizontally oriented, and the specifications of the mechanism may account for such placement. 
     While this specification contains many specifics, these should not be construed as limitations on the scope of an invention that is claimed or of what may be claimed, but rather as descriptions of features specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or a variation of a sub-combination. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. 
     Although embodiments of various methods and devices are described herein in detail with reference to certain versions, it should be appreciated that other versions, methods of use, embodiments, and combinations thereof are also possible. Therefore the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.