附 錄 Shutoff valve for cryogenic liquid storage tank In order to achieve the foregoing objective, the automatic pressure relief means includes a cylindrical housing attached to a vent tube having a seat at one end. The other end of the vent tube is attached to a safety regulator valve to vent gas to the atmosphere. The cylindrical housing is closed except for a hole at its lower end. A steel ball, which has a diameter greater than the hole in the lower end of the housing, is contained within the housing below the seat. As the cryogenic tank is filled, the steel ball first responds to the momentum of the gas escaping through the vent tube and is lifted toward the seat. When the cryogenic liquid reaches the steel ball, the addition momentum of the liquid with its greater mass drives the steel ball into engagement with the seat and substantial halts the escape of gas through the vent tube. Once the steel ball has engaged the seat, the difference in pressure between the gas in the tank and the setting of the safety regulator valve on the vent tube holds the steel ball in place against the seat until the filling operation is complete, and the pressure in the tank has decayed to the operating pressure of the tank. Although the steel ball does not float in the cryogenic liquid, the momentum of the liquid against the steel ball in the enclosed housing is sufficient to drive the steel ball against the seat and substantially seal off the vent tube. A pressure relief means includes a vent tube which extends through the neck and which has an exhaust port at its top end and an internal pressure relief valve at its lower end. The internal pressure relief valve only extends a short distance into the vapor space at the top of the inner vessel . A safety pressure relief valve is connected to exhaust port and has a pressure set point above the operating pressure (emptying pressure) of the tank and below the higher delivery pressure (filling pressure) of the tank. Turning to FIG. 2, the internal pressure relief valve includes a cylindrical housing which is connected to the bottom end of the vent tube. The housing is enclosed except that its lower end has a hole therein to allow entry of gas and liquid . Near the top of the housing 36 there is provided a tapered seat which surrounds an opening leading to the vent tube. Enclosed within the housing is a ball which is formed of steel for example. Other materials may be used as long as they have sufficiently high melting temperatures so that the ball can remain within the housing while the tank is being welding during fabrication. Materials that can withstand the heat of fabrication are too dense to float in the cryogenic liquid in the inner vessel. Consequently one cannot rely on the buoyancy of the ball to force the ball into contact with the tapered seat and close the internal pressure relief valve. I have discovered that the momentum of the cryogenic liquid flowing into the housing can be used to propel the ball into engagement with the tapered seat and substantially close the internal pressure relief valve. In order to fill the tank (FIG. 1), a single delivery hose from a transport tank (not shown) is connected to the inlet/outlet port by means of the coupling and pipe. The vapor pressure in the transport tank causes the cryogenic liquid in the transport tank to flow through the hose, through coupling, through pipe, through pipe, and into the inner vessel. As the cryogenic fluid rises in the inner vessel, the vapor pressure increases until it exceeds the set point of safety pressure relief valve. Once the set point of safety pressure relief valve is exceeded, the vapor escapes (as shown by arrows in FIG. 2) through the internal pressure relief valve, the vent tube, the exhaust port, and the safety pressure relief valve, which has its set point below the pressure of the transport tank. Consequently, the vapor is vented to the atmosphere instead of being compressed above the liquid and creating back pressure sufficient to counteract the vapor pressure in the transport tank. As the vapor escapes through the vent tube, it necessarily passes through the hole and the housing. As the gas passes through the housing, the momentum of the escaping gas causes the steel ball to rise within the housing toward the tapered seat. The steel ball and housing are dimensioned such that the momentum of the gas is not sufficient to drive the steel ball into engagement with the tapered seat. Once the liquid rises to the opening of the enclosed housing, liquid is forced through hole and into the enclosed housing. Because the liquid has a greater mass and therefore greater momentum than the gas, the momentum of the liquid flowing into the housing is sufficient to drive the steel ball into engagement with the tapered seat. To assure proper operation of the internal pressure relief valve, the dimensioning of the steel ball and the enclosed housing is critical. Particularly, in a preferred embodiment of the present invention in which a steel ball is used, I have found that a 1/2 inch steel ball performs satisfactorily when the inside diameter of the housing 36 is 5/8 inch. Moreover, for a steel ball with a diameter of 1/2 inch, the inside diameter of the housing must be 5/8 inch plus or minus 1/32 inch. If the inside diameter of the housing is too small, the momentum of the gas will be sufficient to drive the steel ball into engagement with the tapered seat prematurely closing the internal pressure relief valve and preventing the tank from being completely filled. If, on the other hand, the inside diameter of the housing is too large, the momentum of the liquid will not be sufficient to drive the steel ball into engagement with the tapered seat, and the internal pressure relief valve will not close allowing escape of liquid as the tank continues to fill. If another heat resistant material other than steel is used for the ball, such as a lighter weight heat resistant material, the tolerances on the inside diameter should be less critical. Likewise, using a tapered housing which has a greater diameter at the top and a smaller diameter at the bottom (much like the tapered seat) should likewise provide for less critical dimensional tolerances between the inside diameter of the housing and the diameter of the ball. Once the float ball engages the tapered seat, further escape of liquid or vapor from within the inner vessel is substantially inhibited although the metal to metal contact between the ball and the tapered seat will not provide a complete seal. In the context of the present invention the tapered seat which substantially inhibits the escape of liquid and gas is considered a sealing seat. The use of a sealing gasket such as the O-ring employed by the prior art has been eliminated because such sealing gaskets are generally made of materials that cannot stand the heat of manufacture or if capable of withstanding such heat, are expensive. Moreover, the seal created by the ball and tapered leaks only a small amount of gas and only for the time that the vapor pressure exceed the set point of the safety pressure relief valve. Even after the valve has been substantially closed by means of the steel ball, cryogenic fluid will continue to flow into the tank until the vapor pressure in the vapor space in the inner vessel equals that of the vapor pressure in the transport tank. That further increase in the level of the liquid in the tank increases the internal vapor pressure inside the inner vessel, and the resulting pressure differential between the inside of the inner vessel and the set point of the safety pressure relief valve insures that the steel ball is securely seated against the tapered seat to insure against further significant venting of vapor or escape of liquid during the filling process. Once the cryogenic tank has been filled, the transport tank hose is uncoupled from self-closing coupling. As the gas is subsequently withdrawn from vessel 14 through regulator , the pressure of the vapor will be reduced below the set point of safety pressure relief valve, and the steel ball will drop from engagemnet with the tapered seat. With the steel ball disengaged from tapered seat , the tank is ready for the next filling operation. In filling tank 10 in FIG. 1, the small amount of vapor and liquid that escapes during the filling operation through port is less economically important than the cost of providing a skilled transport operator and/or sophisticated pumping and venting apparatus. Also, the cost of the vented vapor and liquid is small when compared to the cost of additional delivery visits that would result if the tank 10 is only partially filled. There is disclosed an improved internal pressure relief valve for filling a cryogenic liquid storage tank. The internal pressure relief valve consists of a housing with a sealing seat at one end, an inlet hole at the other end, and a ball enclosed therein. The internal pressure relief valve is constructed of materials which can withstand the heat encountered during fabrication without melting. Consequently, the material for the ball is more dense than the cryogenic liquid in the tank so that the ball will not float in the cryogenic liquid. Consequently, the ball and the housing are dimensioned so that the momentum of the cryogenic liquid as it flows into the housing toward a vent port during the filling operation is sufficient to drive the ball into engagement with the sealing seat, closing the vent port, and assuring the termination of the filling process when the pressure in the cryogenic tank builds up to that of the delivery pressure. 低溫液體儲罐 為了實現(xiàn) 低溫 目標，自動泄壓手段包括一個圓柱形住房附在排氣管有座 位的一端。另一端的排氣管連接到一個安全調(diào)節(jié)閥泄氣體排放入大氣。圓柱住房除外關(guān)閉了一個洞在其下端。鋼球，其直徑大于桿下端的，是包含在下面的座位上。由于低溫罐體裝貨，鋼球首先響應的勢頭氣體逸出的排氣管通過。當?shù)蜏匾后w達到鋼球，增加勢頭的液體，它的體積更大驅(qū)動鋼球接觸到所在 的位置和大量阻止氣體外泄通過排氣管。一 但通過 鋼球所在地，不同的壓力之間的罐和確定安全調(diào)節(jié)閥的排氣管擁有鋼球在對席位，直到填充作業(yè)完成后 。 雖然鋼球不浮動的低溫液體，勢頭的液體對鋼球在封閉住房足以驅(qū)動鋼球， 從而 封鎖噴口管。 壓力 救助 手段包括一個管口 延伸，并有一個排氣口在其最高端和內(nèi)部的壓力安全閥在其下端。內(nèi)部壓力安全閥只延長很短的距離到蒸氣空間上方的 距離 。一個安全泄壓閥連接到排氣口和有壓力設(shè)定點以上的工作壓力（排空壓力）的 罐體 和低于更高交付壓力（充氣壓力）的 液罐 。 內(nèi)部壓力安全閥包括一個圓柱形住房這是連接到低端噴口管。住房附除外，其下端有一個洞，使進入其中的 管 和液態(tài)天然氣。上方附近的房屋提供了一個錐形座位周圍開放導致排氣管。封閉的住房球是形成鋼鐵為例。其他材料可用于只要有足夠高的熔化溫度，使球能保持在 一定的位置 ，而 液罐 正在焊接在捏造。材料能 夠經(jīng)受熱加工過于密集浮動的低溫液體。因此，不能依靠浮力球，迫使接觸到錐形座椅和密切的內(nèi)部壓力安全閥。已發(fā)現(xiàn)的勢頭低溫液體流入住房可用于推進球到參與錐形座椅，并大大密切的內(nèi)部壓力安全閥。 為了填補箱，單一的交付軟管從運輸罐連接到進 /出口通過的耦合 器 和管道。蒸氣壓在運輸 罐 造成低溫液體運輸罐流經(jīng)軟管，通過的耦合，通過管道，今日下一管道 通過管道，進入內(nèi)船只。由于低溫流體上升內(nèi)船只，蒸汽壓力的增加，直到超過設(shè)定的安全壓力安全閥。一旦設(shè)定點的安全泄壓閥是超過 指定數(shù) ， 蒸汽 通過內(nèi)部壓力安全閥，通風管， 到達 排氣口， 和安全的壓力溢流閥，其設(shè)置點的壓力，下面的運輸罐。因此，汽是發(fā)泄到大氣中，而不是壓縮以上的液體和創(chuàng)造背壓足以抵消蒸氣壓在運輸罐 。 隨著天然氣穿過住房的勢頭逃避氣體導致鋼球內(nèi)上升對房屋座錐形。鋼球和住房尺度這種勢頭的氣體是不夠的驅(qū)動鋼球到參與圓錐席位。一旦液體二氧化碳上升到 密封 住房，液體被迫通