外文翻译-低温液体储罐.docVIP

附 录 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,