Control device for maintaining the level of a liquified gas in a container between two different limits

Claim 1

A control device for maintaining the level of a liquefied gas in a container between two different limits, the container communicating via a siphon, with the liquid space of a storage container, the vapour space of which can be made to communicate with a vapour outlet, said control device comprising a first vapour pressure bulb arranged at the higher limit and a second vapour pressure bulb arranged at the lower limit, the bulbs containing a medium under pressure which condenses at the temperature of the liquefied gas, the medium pressures being capable of actuating first and second control valves in such a manner that the communication of the vapour space of the storage container with the vapour outlet is interrupted by the said valves when the level of the liquefied gas in the container drops below the lower limit, and is released when the level exceeds the higher limit, characterized in that the first control valve is constituted by a first piston-like member which is incorporated in a first housing and can reciprocate therein in the axial direction and which constitutes with its one end face a wall of a first space which is in open communication with the first vapour pressure bulb and is otherwise closed, and constitutes with its other end face also the boundary of a second space which is in open communication with the second vapour pressure bulb, the second space furthermore comprising a communication which, when the first piston-like member reciprocates, is alternately closed and released by said member, the second control valve being constituted by a second piston-like member which is accommodated in a second housing with some amount of play and can reciprocate therein in the axial direction, and which constitutes with its one end face a wall of a third space which communicates with the communication with the second space and is otherwise closed and with its other end face also constitutes the boundary of a fourth space which communicates with an auxiliary vessel containing a pressure medium, the second piston-like member upon reciprocation being capable of communicating the vapour space of the storage container alternately with the fourth space and the vapour outlet, the medium pressures in the vapour pressure bulbs, the pressure medium pressure in the auxiliary vessel, and the surface areas of the end faces of the piston-like members being furthermore chosen to be so that, when the level of the liquefied gas in the container lies below the second vapour pressure bulb, the resulting force on the first piston-like member causes said member to assume a position in which the second space is in open communication with the third space and the resulting force on the second piston-like member causes the said member to assume a position in which the vapour space of the storage container is in open communication with the fourth space, in which, when the said level rises due to siphoning action, when the second vapour pressure bulb is reached the resulting force on the first pistonlike member causes said member to interrupt the communication between the second and the third space with a remaining medium pressure in the third space, in which the second piston-like member maintains the open communication between the vapour space and the fourth space, in which, when the said level reaches the first vapour pressure bulb, the resulting force on the first piston-like member causes said member to assume a position in which the open communication between the second and the third space is restored, and, as a result of the falling medium pressure in the third space, the second piston-like member interrupts the communication between the vapour space and the fourth space and produces an open communication between the vapour space and the vapour outlet.