Fluid handling – Destructible or deformable element controlled – Destructible element
Patent
1992-12-01
1994-11-22
Schwardron, Martin P.
Fluid handling
Destructible or deformable element controlled
Destructible element
137495, 137526, F16K 1732, F16K 1740
Patent
active
053659643
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a vacuum valve to be used in an emergency system to reduce the risk of escape of liquid from tankers due to injuries under the waterline, e.g. caused by grounding.
In connection with various tanker disasters which have resulted in comprehensive environmental detriment, efforts have been displayed in many quarters, including authorities and classification agencies, to develop principles for such emergency systems, but it has been found difficult to establish standards which can be generally observed without considerable excess expenses and inconvenience to the trade.
The fundamental concept presenting itself for such emergency systems can briefly be described as follows:
Only escape from injuries under the waterline will be considered, because the possibilities of dealing with injuries above the waterline are practically nil.
For injuries occurring under the waterline it is attempted to reduce the escape by closing all inlets to the tank, so that an escape will rapidly create a vacuum which prevents the part of the cargo still present in the tank from flowing out into the surrounding environment.
By studies and calculations it has been ascertained that the closing of the inlets to the tank must be completed within a time interval of 5 to 10 seconds and therefore will have to be effected automatically. A possible solution would be an arrangement e.g. controlled by a level sensor which in response to a sudden drop of level automatically activates an isolation of the cargo tank, e.g. by means of hydraulically controlled stop valves. To maintain the vacuum thereby created in the tank, a vacuum pump or ejector may subsequently be set in operation for continuously removing the vapors developed owing to the change of boiling point of the cargo. However, the most critical phase is the fastest possible closing of all inlets to the tank with the greatest possible certainty. For a tanker in voyage the inlets will first and foremost be the vacuum valves with which a tanker is usually equipped for the purpose of relieving vacuum in the tank caused by temperature variations or during unloading of the tank.
It is the object of the invention to provide a vacuum valve, which in response to the outflow of a large quantity of liquid per time unit, such as will occur at the initiation of an escape from an injury under the waterline of a tanker, is automatically self-blocking and is-therefore ideally suitable for emergency systems of the kind considered.
The invention is applicable to a vacuum valve of the well known kind comprising a valve housing connected to the top of a tank of the tanker and having a valve opening with a valve seat, a valve body within said valve housing serving to close and open said valve opening, said valve body having an outer side subjected to the pressure of the atmosphere outside said valve housing and an inner side subjected to the pressure in the interior of said tank, said valve body being subjected to a built-in closing force counteracted by an opening force, the valve being opened when said opening force resulting from the pressure difference between the outer and inner side of the valve body is positive and exceeds said built-in closing force during outflow of liquid from the tank so that then air is sucked in through the valve opening and creates a pressure drop from the atmosphere across the valve to the interior of the valve housing, said pressure drop increasing with the rate of inflow of air.
A vacuum valve of this kind is illustrated in the drawing of U.S. Pat. No. 3,999,471.
To achieve the object set forth above, a vacuum valve of the kind referred to is provided with stand-by biasing means to cause a supplemental biasing closing force which is applied to said valve body to close said valve opening in response to the occurrence of a pressure drop across said valve beyond a predetermined critical value.
At the initiation of an escape from an injury under the waterline of a tanker, a vacuum valve constructed as set forth is immediately closed as a direct consequen
REFERENCES:
patent: 2732856 (1956-01-01), Jurs et al.
patent: 4518014 (1985-05-01), McAlpine
patent: 4844113 (1989-07-01), Jones
patent: 5213127 (1993-05-01), Sorensen
Lee Kevin L.
Schwardron Martin P.
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