Abstract:
A vent and relief valve having a valve body that is in fluid communication with the interior of a tank containing a fluid. A vent valve and relief valve are positioned within the valve body. The vent valve is capable of being configured into an open position to vent fluid from the interior of the tank. The relief valve is capable of being configured into an open position to relieve pressure within a tank. The relief valve is also capable of engaging the vent valve to form a seal to substantially prevent fluid from flowing from the tank. The valve body also includes a valve seat having a first surface that releasably engages the vent valve when the vent valve is in a closed position and a second surface that releasably engages the relief valve when the relief valve is in a closed position.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is directed to coaxial flow vent and relief valves for pressurized fluid tanks, ullages and ducts. In particular, the present invention is directed, but not limited to, vent and relief valves for use in cryogenic liquefied gases and hydrocarbon fuel space launch vehicle rocket propellant tank applications.  
       BACKGROUND OF THE INVENTION  
       [0002]     Pressurized propellant tanks, including tanks for storage of cryogenic liquefied gases, such as oxygen and hydrogen, and liquid hydrocarbons, such as kerosene, generally include a vent opening at the top thereof. Vent and relief valves are typically mounted on the top of the tanks. Alternatively, the vent and relief valves are mounted in the discharge vents of the tanks. The vent and relief valves provide a vent function and a pressure relief function. The vent function includes the ability for the vent and relief valve to vent the tank, such as during the filling of the tank or when it is otherwise desirable to release large quantities of gas from the tank. Launch vehicle propellant tanks are usually pressurized to enhance the structural stability of the tanks, and to ensure a net positive suction head (NPSH) to prevent cavitation of the turbopumps that are generally used in these systems. The relief function provides pressure relief to avoid overpressurization of the tank when the vent is closed. The relief function allows safe operation of the tank by maintaining the pressure of the tank below a predetermined, safe pressure.  
         [0003]     One known form of vent and relief valve is a non-coaxial flow device containing a main valve member that axially slides in a bore of the valve body and which is linked to an actuator operated by externally applied gas, such as helium. When pressurized with gas, the actuator moves the main valve open to vent the tank of ullages gas and/or cryogenic liquid boil-off gas, such as during the filling of the tank with a liquid cryogenic fuel or propellant. Alternately, the relief valve modulates to an open position by action of an integral pilot valve and actuator piston to automatically prevent tank pressure from exceeding a predetermined value. This known form of vent and relief valve is often mounted on top of and outside of a tank, requiring vertical installation space. The non-coaxial flow path around the main flow element is tortuous and significantly impedes flow exhausting from the tank. Only a single outlet port can be conveniently and practically incorporated in this known form of vent and relief valve, so an additional flow splitter must be added at the valve outlet to direct flow into two diametrically opposing discharge exhausts to mitigate side thrust on the tank. It also is possible that the main valve could jam or stick in the sliding bore of the body as a result of cyclic wear induced material galling, particulate contamination, thermal distortion or any combination thereof. This single point failure would cause both the vent and relief operating modes to be degraded or totally inoperative, allowing the possibility of overpressurization and catastrophic failure of the tank.  
         [0004]     Another vent and relief valve known in the art includes the coaxial vent and relief valve disclosed in U.S. Pat. No. 3,945,295 to Reinicke, which is herein incorporated by reference in its entirety. In the Reinicke patent, a vent valve and relief valve are arranged coaxially in the valve body to minimize the flow impedance of non-coaxial vent and relief valves. The vent valve and relief valve have interengaged seats to prevent escape of pressurized fluid. In particular, the Reinicke patent includes a poppet vent valve which seats against a relief bellows seat. Engagement of the poppet against the bellows seat provides the seal preventing the flow of fluid through the valve. During vent mode operation, the poppet disengages from the bellows seat through the operation of an externally gas pressurized actuator and provides a space through which fluid is permitted to flow. Alternately, during relief mode operation, when the pressure within the tank exceeds a pre-determined pressure, the interior of the dual bellows is reduced in pressure by the venting action of the pilot valve, creating a pressure differential that compresses the bellows, disengaging the bellows seat from the poppet valve, allowing fluid to travel through the valve and preventing pressure buildup in the tank. The venting continues until the tank pressure is reduced to the desired level. The Reinicke patent valve does not have a single point failure that can simultaneously disable both the relief and vent operating modes, which increases reliability in critical space vehicle applications. The Reinicke patent valve has the drawback that the bellows of the relief valve are not protected from damage, particularly during installation into the tank. Further, the Reinicke patent has independent and separate travel stops for the vent mode poppet and relief mode seat, making valve assembly and adjustment more tedious and providing for a less consistent and reliable operation under thermal transient conditions. The Reinicke patent also has the drawback that it has a single outlet providing for a valve having a relatively large height from the top of the tank, taking up valuable space, for example, in a space launch vehicle. The single outlet has the further disadvantage that a side thrust force is created during the vent and/or relief functions of the valve due to the fluid exhausting from the single outlet duct, and a special flow splitter with diametrically opposing outlets must be added to mitigate side thrust force.  
         [0005]     What is needed is a vent and relief valve that is more compact, that provides for easier assembly and more precise travel stop settings, that provides more consistent operation under thermal transient conditions, that provides protection for the relief valve mechanism during installation, that more conveniently mitigates side thrust, and that does not suffer from the drawbacks of the prior art.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention includes a vent and relief valve, particularly for use with cryogenic liquefied gas and hydrocarbon fuel storage tanks. The vent and relief valve has a valve body that is in fluid communication with the interior of a tank containing a fluid. A valve body includes a vent valve and a relief valve. The vent valve is capable of being configured into an open position to vent fluid from the interior of the tank. The relief valve is capable of being configured into an open position to relieve pressure within the tank when the pressure within the tank exceeds a predetermined pressure. The relief valve is also capable of engaging the vent valve to form a seal to substantially prevent fluid from flowing from the tank. The vent valve and relief valve are positioned in a coaxial configuration. The vent and relief valve also includes a valve seat having a first surface that releasably engages the vent valve when the vent valve is in a closed position. The valve seat further includes a second surface that releasably engages the relief valve when the relief valve is in a closed position.  
         [0007]     The present invention also includes an embodiment of a vent and relief valve having a plurality of outlet ducts. The vent and relief valve according to this embodiment has a valve body that is in fluid communication with the interior of a tank containing a fluid. A valve body includes a vent valve and a relief valve. The vent valve is capable of being configured into an open position to vent fluid from the interior of the tank. The relief valve is capable of being configured into an open position to relieve fluid pressure within the tank when the fluid pressure within the tank exceeds a predetermined pressure. The relief valve is also capable of engaging the vent valve to form a seal to substantially prevent fluid from flowing from the tank. The vent valve and relief valve are positioned in a coaxial configuration. The vent and relief valve also includes a valve seat having a first surface that releasably engages the vent valve when the vent valve is in a closed position. The vent and relief valve further includes a second surface that releasably engages the relief valve when the relief valve is in a closed position. The vent and relief valve further includes a plurality of outlet ducts in fluid communication with the valve body. The outlet ducts allow discharge of fluid when either or both of the vent valve and relief valve are in the open position.  
         [0008]     The present invention also includes an embodiment of a vent and relief valve having a plurality of outlet ducts and an actuator mechanism that is at least partially recessed into the valve body. The vent and relief valve according to this embodiment has a valve body that is in fluid communication with the interior of a tank containing a fluid. A vent valve is positioned within the valve body. The vent valve is capable of being configured into an open position to vent fluid from the interior of the tank. A relief valve is also positioned within the valve body. The relief valve is capable of being configured into an open position to relieve pressure within the tank when the pressure within the tank exceeds a predetermined pressure. The relief valve is also capable of engaging the vent valve to form a seal to substantially prevent fluid from flowing from the tank. The vent valve and relief valve are positioned in a coaxial configuration. The vent and relief valve also includes a valve seat having a first surface that releasably engages the vent valve when the vent valve is in a closed position. The vent and relief valve further includes a second surface that releasably engages the relief valve when the relief valve is in a closed position. The vent and relief valve further includes a plurality of outlet ducts in fluid communication with the valve body. The outlet ducts allow discharge of fluid when either or both of the vent valve and relief valve are in the open position.  
         [0009]     The present invention further includes a method for venting or relieving pressure on a tank. The method includes providing a tank for storage of cryogenic liquefied gases and a vent and relief valve in communication with the interior of the tank. The valve and relief valve have a vent valve and relief valve being arranged and disposed in a coaxial configuration. A pressure in the interior of the tank is sensed. The relief valve is configured into an open position in response to a predetermined pressure sensed in the interior of the tank. The relief valve is configured into a closed position in contact with a valve seat when the sensed pressure in the interior of the tank is less than the predetermined pressure. The vent valve is configured into an open position when venting of cryogenic liquefied gases from the interior of the tank is desired. The vent valve is configured into a closed position when no venting of cryogenic liquefied gases from the interior of the tank is desired.  
         [0010]     An advantage of the present invention is that the dual stop guard provides a stop for both the relief valve and a stop for the vent valve.  
         [0011]     Another advantage of the present invention is that the dual stop guard provides protection for the relief valve, particularly during installation. In particular, the embodiment of the invention including metallic bellows in the relief valve are protected from damage.  
         [0012]     Still another advantage of the present invention is that the dual stop guard permits the valves to seat against each other and provide an improved seal, while still providing a stop for both the vent valve and the relief valve.  
         [0013]     Still another advantage of the present invention is that the multiple outlet provides smaller outlet ducts from the valve. Smaller outlet ducts permit the valve to have a reduced height, while maintaining relief and vent capacity. The reduced height reduces the space required for the valve and allows a greater amount of area for other components in an application such as a space launch vehicle.  
         [0014]     Still another advantage of the present invention is that the multiple outlet ducts provides fluid relief resulting in reduced side or internal thrust. In one embodiment having a dual outlet duct, the thrust may be equalized in order to substantially prevent thrust in a single direction.  
         [0015]     Still another advantage of the present invention is that the multiple outlet ducts provides an increased area of venting, allowing the recess of the actuator into the valve further reducing the height of the valve. The reduced height reduces the space required for the valve and allows a greater amount of area for other components for the launch vehicle.  
         [0016]     Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a perspective view of a vent and relief valve according to an embodiment of the present invention.  
         [0018]      FIG. 2  is a cutaway schematic view of a vent and relief valve in a closed position according to an embodiment of the present invention.  
         [0019]      FIG. 3  is a cutaway schematic view of the vent and relief valve shown in  FIG. 2  with the vent valve in an open position.  
         [0020]      FIG. 4  is a cutaway schematic view of the vent and relief valve shown in  FIG. 2  in pressure relief position.  
         [0021]      FIG. 5  is a cutaway schematic view of a vent and relief valve in a closed position according to an alternate embodiment of the present invention.  
         [0022]      FIG. 6  is a cutaway schematic view of the vent and relief valve shown in  FIG. 5  with the vent valve in an open position.  
         [0023]      FIG. 7  is a cutaway schematic view of the vent and relief valve shown in  FIG. 5  in a pressure relief position.  
         [0024]      FIG. 8  is a cutaway schematic view of a vent and relief valve according to an alternate embodiment of the present invention.  
         [0025]      FIG. 9  is a cutaway schematic view of a vent and relief according to an alternate embodiment of the present invention. 
     
    
       [0026]     Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0027]      FIG. 1  shows a perspective view of a vent and relief valve according to an embodiment of the present invention. The vent and relief valve includes a valve body  101  which attaches to a tank (not shown) by attachment flange  103 . The tank may contain a pressurized fluid, such as, for example, cryogenic liquefied oxygen, hydrogen, or hydrocarbon liquid, such as kerosene. The valve body  101  also includes a pilot valve  105  that operates a relief valve  109 . The relief valve  109  is a bellows structure having a relief valve seat portion  110  that is capable of being drawn up into an open position to release fluid from the tank gas ullages. The valve body  101  further includes an actuator mechanism  107  that operates a vent valve  111 . The vent valve  111  is a poppet valve that extends from the base of the valve which is adjacent to the fluid in the tank upward toward the valve body  101  into the actuator mechanism  107 . A valve stop  113  is coaxial positioned coaxially with respect to the relief valve  109  and the vent valve  111  and provides protection for the relief valve  109 . The valve stop  113  provides a structure that prevents the bellows of the relief valve  109  from contacting the tank or other equipment during installation, reducing the chances that the bellows is damaged or punctured. The valve stop  1   13  extends from the valve body  101  into the tank from the attachment flange  103 . The valve stop  113  includes openings  115 , which permit flow of fluid from the tank when the relief valve is in the open position. The configuration of the openings can be any configuration of openings that permits fluid to pass, particularly when the valve is in the relief position. Preferably, the valve includes openings at least partially circumferentially around the valve stop. When the vent valve  111  and/or relief valve  109  are in the open position, fluid travels through the valve body  101  and exhausts through an outlet duct  104 .  FIG. 1  shows the vent valve  111  in a closed position. The vent valve  111  includes a plurality of vent valve tangs  119 , which extend outward from the center axis of the vent valve. The valve stop  113  also includes a vent valve stop surface  117 , which releasably engages vent valve tangs  119 . When the vent valve  111  is in the closed position, the vent valve tangs  119  engage the valve stop surface  117  and maintain the position of the vent valve  111 . The actuator mechanism  107  preferably provides an upward force on the vent valve  111  when the vent valve  111  is not activated to maintain engagement of vent valve tangs  119  and the vent stop surface  117 . The relief valve seat portion  110  engages the vent valve  111  and provides a seal that substantially prevents the flow of fluid through the valve. The separate actuator mechanism  107  and pilot valve  105  permits independent operation of each of the vent valve  111  and the relief valve  109 . Although  FIG. 1  shows the vent and relief valve in the closed position, either or both of the vent valve  111  or relief valve  109  may be moved to release fluid from the tank.  
         [0028]      FIG. 2  shows a vent and relief valve in a closed position according to one embodiment of the present invention. As in  FIG. 1 , the vent and relief valve includes a valve body  101 , which is mounted on a tank by attachment flange  103 . The vent and relief valve includes a vent valve  111  and a relief valve  109  positioned in a coaxial arrangement. Unlike the embodiment shown in  FIG. 1 , the valve stop  113  forms a cylinder encircled by the relief valve  109 . Similar to the embodiment shown in  FIG. 1 , the valve stop  113  includes one or more openings (not shown in  FIG. 2 ) that permit the flow of fluid through the valve when the relief valve  109  is in the open position. The valve stop includes a relief valve stop surface  201  and a vent valve stop surface  203 . The relief valve stop surface  201  provides a surface that releasably engages the relief valve seat portion  110  and prevents the relief valve  109  from opening further when the relief valve is in the fully open position. The vent valve stop surface  203  provides a surface that releasably engages the vent valve  111  and prevents the vent valve from closing further when the vent valve is in the closed position.  
         [0029]      FIG. 2  shows the vent and relief valve in the closed position, where the relief valve seat portion  110  engages the vent valve  111  and forms a seal that substantially prevents the flow of fluid from the tank through the vent and relief valve. Also, the vent valve  111  engages the vent valve stop surface  203 . The vent valve  111  is positioned by use of an actuator  107 . The actuator mechanism  107  includes a piston  205  and a spring  207 . The spring  207  provides a force urging the vent valve  111  toward the valve stop  113  when the actuator mechanism  107  is not activated. To activate the actuator mechanism  107 , a fluid, such as helium or air, is allowed to flow into the piston  205 , generating a force for urging the piston toward the attachment flange  103 , compressing the spring  207 . As the piston  205  moves, the vent valve  111  likewise moves and disengages from the vent valve stop surface  203  of the valve stop  113  (see  FIGS. 3 and 6 ). To close the vent valve  111 , a sufficient amount of the fluid in the piston is permitted to escape and the spring overcomes the piston fluid force, the spring decompressing to draw the vent valve  111  toward the valve stop  113 , until the vent valve  111  engages the vent valve stop surface  203 . Although the actuator  107  is shown as a piston  205  and spring  207  arrangement, the actuator mechanism  107  may be any device that is capable of positioning the vent valve  111  in an open or closed position. The vent valve  111  may be fabricated from any suitable material that can be formed into a poppet valve and can operate in cryogenic temperatures. The vent valve is preferably fabricated from a metal, such as nickel-based superalloy, aluminum alloy, titanium alloy, stainless steel or combinations thereof.  
         [0030]     The valve body  101  also includes a relief valve  109 . The relief valve  109  includes a bellows arrangement, forming a cylinder coaxial with the vent valve  111 . The bellows arrangement of the relief valve  109  is preferably a metallic bellows capable of opening and closing (i.e., contracting and expanding) in response to fluid pressure within the bellows to permit or prevent the flow of fluid from the tank. The relief valve  109  may be fabricated from any suitable material that can be formed into a bellows and can operate in cryogenic temperatures. However, the relief valve is preferably fabricated from a metal, such as nickel-based superalloys, aluminum alloy, titanium alloy, stainless steel, or combinations thereof. The relief valve  109  further includes relief valve seat portion  11   0 . When the relief valve  111  is in the fully open position, the relief valve seat portion  110  is engaged on the relief valve stop surface  201 . Pilot valve  105  senses the pressure within the tank through pressure sensing line  209 . If the pressure in the tank exceeds a predetermined pressure, the pilot valve  105  opens a pilot vent  211  to bellows vent  213 , which exhausts fluid from and reduces the pressure in the interior of the bellows to a level that is less than the tank pressure. This establishes a pressure differential across the bellows as compared to the tank pressure, creating a force that compresses the bellows. In other words, the interior volume of the bellows is reduced. As the bellows contracts, the relief valve  109  and the relief valve seat portion  110  is drawn upward away from the vent valve  111 . Once the relief valve  109  disengages from the vent valve  111 , fluid above the tank ullages is permitted to travel through the openings in the valve stop  113 , through the valve body  101  and out the outlet duct  104  (see  FIGS. 4 and 7 ). Ullages, as used herein, is defined as an amount of fluid that a container lacks of being full. Although  FIGS. 2-7  show a pilot valve  105  having a pressure sensing capsule arrangement, the pilot valve  105  may be any valve arrangement that is capable of measuring the pressure within the tank and increasing and decreasing the pressure inside the bellows to expand and contract the bellows of the relief valve  109  in response to the pressure in the tank.  
         [0031]     Unlike the embodiment shown in  FIG. 1 , the embodiment shown in  FIG. 2  includes a separate relief valve guard  215 , which guides the bellows of the relief valve  109  as the bellows expands and contracts and protects the bellows from damage, particularly from impacts from the tank or other equipment that may occur during installation.  
         [0032]      FIG. 3  shows the vent and relief valve shown in  FIG. 2  with the vent valve  111  in the open position.  FIG. 3  has the substantially the same arrangement of valve body  101 , attachment flange  103 , pilot valve  105 , actuator mechanism  107 , relief valve  109 , vent valve  111 , valve stop  113 , and relief valve guard  215  as shown in  FIG. 2 .  FIG. 3  shows the vent valve  111  in the open position. In order for the vent valve  111  to be positioned in the open position, the actuator mechanism  107  is activated. To activate the actuator mechanism  107 , a fluid  301 , preferably helium gas, is permitted to flow into and pressurize piston  205 , urging forcing the piston  205  to compress spring  207 , which moves vent valve  111  away from the valve body. As the vent valve  111  moves downward away from the valve body, the relief valve  109  and the relief valve seat portion  110  extend and engage the valve stop  113  at relief valve stop surface  201 . As the vent valve  111  disengages from the relief valve seat portion  110 , the relief valve  109  and the relief valve seat portion  110  extend and engage the valve stop at relief valve stop surface  201 . Once the vent valve  111  disengages from both the vent valve stop surface  203  and the relief valve seat portion  110 , fluid  310  from the tank is permitted to flow between the vent valve  111  and the engaged relief valve seat portion  110 , through the valve body  101  and out through the outlet duct  104  as shown. The positioning of the vent valve  111  into the open position preferably takes place during the filling or the tank and/or when a large quantity of fluid is to be exhausted from the tank ullages. In an alternate embodiment of the present invention, an increased flow of fluid  310  through the vent and relief valve is achieved when the vent valve is in the open position by drawing the relief valve  109  toward the valve body  101 . As the bellows of the relief valve  109  is contracted, the relief valve seat portion  110  is drawn upward toward the valve body  101  providing a greater area for fluid flow from the tank ullages.  
         [0033]      FIG. 4  shows the vent and relief valve shown in  FIG. 2  with the relief valve  109  in the open position.  FIG. 4  has the substantially the same arrangement of valve body  101 , attachment flange  103 , pilot valve  105 , actuator mechanism  107 , relief valve  109 , vent valve  111 , valve stop  113 , and relief valve guard  215 , as shown in  FIG. 2 . The pilot valve  105  senses the pressure in the tank through pressure sensing line  209 . If the pressure in the tank exceeds a predetermined pressure, the pilot valve opens pilot vent  211  to bellows vent  213 , which exhausts fluid from and reduces the pressure inside of the bellows to level that is less than the tank pressure. This creates a pressure differential and force that urges the bellows to contract, which moves the relief valve seat portion  110  upward toward the valve body  101  and away from the vent valve  111  and the relief valve stop surface  201 . Once the relief valve seat portion  110  disengages from the vent valve  111 , fluid  310  from the tank is permitted to flow between the relief valve seat portion  110  and the vent valve  111 , through openings  115  (not shown in  FIG. 4 ) in the valve stop  113 . The fluid  310  from the tank travels through the valve body  101  and out of the vent and relief valve through the outlet duct  104 . The positioning of the relief valve  109  into the open position preferably takes place when the pressure in the tank exceeds the predetermined pressure desired within the tank. The predetermined pressure is preferably a pressure set for safe operation of the tank.  
         [0034]      FIG. 5  shows a vent and relief valve in a closed position according to an alternate embodiment of the present invention.  FIG. 5  includes a cutaway schematic view of the vent and relief valve shown in  FIG. 1 .  FIG. 5  has the substantially the same arrangement of valve body  101 , attachment flange  103 , pilot valve  105 , actuator mechanism  107 , relief valve  109 , and vent valve  111 , as shown in  FIG. 2 . The operation of the actuator mechanism  107 , including the spring  207  and piston  205  and the pilot valve  105 , including the pressuring sensing line  209 , the pilot vent  211  and the bellows vent  213 , is substantially the same as shown in  FIGS. 2-4 . However, unlike the embodiment shown in  FIGS. 2-4 , a valve stop  113  is positioned outside the bellows of the relief valve  109 , encircling the relief valve  109  to provide a position to seat the vent valve  111  and the relief valve  109  as well as protection for the bellows of the relief valve  109 . Valve stop  113  has a relief valve stop surface  201 , which detachably engages the relief valve seat portion  110 . The valve stop  113  also has a vent valve stop surface  203 , which detachably engages the vent valve  111 . The valve stop  113  includes openings  115  (see  FIG. 1 ), which allow the flow of fluid when the relief valve  109  is in the open position. Also unlike  FIG. 2 , the vent valve includes a plurality of tangs  119 , which extend from the vent valve  111 . The tangs  119  engage the vent valve stop surface  203  of the valve stop  113  when the vent valve  111  is in the closed position. The tangs  119  may be fabricated in any geometry suitable for engaging vent valve stop surface  203  and positioning the vent valve in the closed position. Although  FIG. 1  shows the three tangs  119 , any number of tangs  119  may be used, including a solid disk-like geometry extending from the vent valve  111 .  FIG. 5  shows the vent and relief valve in the closed position, where the vent valve  111  is engaged with the relief valve seat portion  110 . The engagement between the vent valve  111  and the relief valve seat portion  110  forms a seal that substantially prevents the flow of fluid through the valve body  101 . The embodiment shown in  FIG. 5  further includes a ring seal  501 , which further improves the seal between the vent valve  111  and the relief valve seat portion  110 . The present invention is not limited to the ring seal  501  shown in  FIG. 5 . The seal may be formed by the direct engagement of the vent valve  111  and the relief valve seat portion  110  or by any suitable seal known in the art. A preferred type of ring seal  501  includes an o-ring, preferably made of a polymer material, such as polytetrafluoroethylene for cryogenic use, and an elastomer, such a fluoroelastomer polymer, for non-cryogenic use.  
         [0035]      FIG. 6  shows the vent and relief valve shown in  FIG. 5  with the vent valve  111  in the open position.  FIG. 6  has substantially the same arrangement of valve body  101 , attachment flange  103 , pilot valve  105 , actuator mechanism  107 , relief valve  109 , vent valve  111 , valve stop  113 , and relief valve guard  215  as shown in  FIG. 5 . The operation of the actuator  107  is substantially the same as the operation shown and described with respect to  FIG. 3 . As the vent valve  111  is moved downwardly away from the valve body  101 , the tangs  119  of the vent valve  111  disengage from the vent valve stop surface  203  of the valve stop  113  and the ring seal  501  of the vent valve  111  disengages from the relief valve seat portion  110 . As the vent valve  111  moves downwardly away from the valve body  101 , the relief valve  109  and the relief valve seat portion  110  extend and engage the valve stop  113  at relief valve stop surface  201 . Once both the tangs  119  and the ring seal  501  are disengaged, fluid  310  is allowed to flow from the tank through the valve body  101  and out through the outlet duct  104 . As in  FIG. 3 , the positioning of the vent valve  111  into the open position, as shown in  FIG. 6 , preferably takes place during the filling or the tank or when a large quantity of fluid  310  is to be exhausted from the tank ullages. In an alternate embodiment of the present invention, an increased flow of fluid  310  through the vent and relief valve is achieved when the vent valve is in the open position by drawing the relief valve  109  toward the valve body  101 . As the bellows of the relief valve  109  is contracted, the relief valve seat portion  110  is drawn upwardly toward the valve body  101  providing a greater area for fluid flow from the tank.  
         [0036]      FIG. 7  shows the vent and relief valve shown in  FIG. 5  with the relief valve  109  in the open position.  FIG. 7  has substantially the same arrangement of valve body  101 , attachment flange  103 , pilot valve  105 , actuator mechanism  107 , relief valve  109 , vent valve  111 , valve stop  113 , and relief valve guard  215 , as shown in  FIG. 5 . The operation of pilot valve  105  is substantially the same as the operation shown and described with respect to  FIG. 4 . If the pressure exceeds a predetermined pressure, the pilot valve  105  exhausts fluid from and reduces the pressure in the interior of the bellows to a level that is less than the tank pressure. This creates a pressure differential across the bellows that contracts the bellows and moves the relief valve seat portion  110  upwardly away from the ring seal  501  portion of the vent valve  111  and the relief valve stop surface  201 . Once the relief valve seat portion  110  disengages from the ring seal  501 , fluid  310  from the tank ullages is permitted to flow through the openings  115  (see  FIG. 1 ) in the valve stop  113 , between the relief valve seat portion  110  and the vent valve  111 , through the valve body  101  and out through the outlet duct  104 . As in  FIG. 4 , the positioning of the relief valve  109  into the open position preferably takes place when the pressure in the tank exceeds the predetermined pressure desired within the tank. The predetermined pressure is typically a pressure set for safe operation of the tank.  
         [0037]      FIG. 8  shows a dual outlet duct, where the outlet duct  104  extends from the center axis of the valve in two opposite directions. When fluid is released, by either or both of the relief valve  109  or the vent valve  111 , fluid  310  exits the tank ullages through the valve body  101 , and into the outlet duct  104 . The outlet duct  104  having the dual outlet permits the flow of fluid  310  to split and exit from the valve in substantially equal portions in each direction. The split flow equalizes any lateral forces due to thrust created by the exit of fluid. The lateral forces of a single outlet can be undesirable in space launch vehicle applications. Therefore, the equalization of the lateral forces is particularly desirable in space launch vehicle applications. In addition to equalizing the force resulting from the exiting fluid, the use of multiple exits for fluid permits each of the individual outlet ducts  104  to be smaller in diameter, where the total capacity to exhaust fluid is at least as large as the single outlet duct  104 , as shows in  FIGS. 1-7 . Since, the diameters of the outlet ducts  104  are smaller, the total height of the vent and relief valve from the surface of the tank is reduced, providing a greater space for other equipment. Greater space for additional equipment is particularly beneficial in launch vehicle applications where space is critical. The vent and relief valve of  FIG. 8  also includes a pilot valve  105  (not shown in  FIG. 8 ) preferably mounted at the junction of the multiple outlet ducts  104 . Although  FIG. 8  shows the flow directed in two directions, any number of outlet ducts may be used, as long as sufficient space near the attachment flange  103  is provided to mount and operate a pilot valve  105  and sufficient symmetry is provided to equalize lateral forces due to exiting fluid. Each additional outlet duct  104  beneficially decreases the height requirement for the valve from the surface of the tank.  
         [0038]      FIG. 9  shows an alternate embodiment of the dual outlet duct, where the actuator mechanism  107  is recessed into the valve body  101 . Since the actuator mechanism is recessed into the valve body  101 , the total height of the vent and relief valve from the surface of the tank is reduced, providing a greater space for other equipment. Similar to  FIG. 8 , the vent and relief valve of  FIG. 9  also includes a pilot valve  105  (not shown in  FIG. 9 ) preferably mounted at the junction of the multiple outlet ducts  104 . Although  FIG. 9  shows the actuator mechanism  107  fully recessed into the valve body  101 , the actuator mechanism  107  may also be partially recessed to provide increased flow and smaller diameter valve body  101 . Further, other components of the vent and relief valve may be recessed into the valve body  101 , such as the pilot valve  105  to reduce the amount of space that the valve occupies exterior to the tank.  
         [0039]     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.