Methods and apparatus for maintaining equilibrium pressure in a container

Abstract

A system for maintaining a gas in equilibrium with a liquid stored in a container with the gas. The system includes a sensor to detect an equilibrium condition within the container, and to generate a first signal in response. A source gas connection allows a pressurized source gas to flow to the container, and a source gas control valve controls flow of the source gas to the container. The system further includes a controller configured to receive the first signal, and also to determine when fluid is removed from the container. The controller is further configured to operate the source gas control valve to allow the source gas to flow into the container when the controller determines that fluid has been removed from the container. The controller allows the source gas to flow into the container until an equilibrium pressure is reached which is a function of the first signal.

I claim:  
     
         1 . A system for maintaining a gas in equilibrium with a liquid stored in a container with the gas, comprising: 
 a sensor configured to detect an equilibrium condition within the container and to generate a first signal in response thereto;    a source gas connection configured to allow a pressurized source gas to flow to the container;    a source gas control valve configured to control the flow of the source gas to the container; and    a controller configured to receive the first signal, to determine when fluid is removed from the container, and, when the controller determines that fluid is removed from the container, to operate the source gas control valve to allow the source gas to flow to the container to establish an equilibrium pressure within the container, the equilibrium pressure being a function of the first signal.    
     
     
         2 . The system  claim 1 , and wherein the sensor is a pressure sensor, the first signal is a pressure signal, and the equilibrium pressure is essentially equal to the pressure signal at a time prior to a time when the controller determines that fluid has been removed from the container.  
     
     
         3 . The system  claim 1 , and wherein: 
 the controller comprises a look-up table of a plurality of determined equilibrium    pressures as a function of temperature; and    the sensor is a temperature sensor, the first signal is a temperature signal, and the equilibrium pressure is established as the determined equilibrium pressure which corresponds to the temperature signal.    
     
     
         4 . The system  claim 3 , and further comprising a pressure sensor configured to determine gas pressure within the container and to generate a pressure signal in response thereto, and wherein the plurality of determined equilibrium pressures is further a function of pressure, and the equilibrium pressure is further established as the determined equilibrium pressure which corresponds to the pressure signal.  
     
     
         5 . The system  claim 1 , and wherein the controller comprises a readable memory device containing a series of executable instructions configured to be executed by the controller to determine the equilibrium pressure as a function of the first signal.  
     
     
         6 . The system  claim 5 , and wherein the series of executable instructions are further configured to be executed by the controller to calculate an equilibrium pressure when a container is placed in an initial fluid communication with the source gas connection.  
     
     
         7 . A system for maintaining a gas in equilibrium with a liquid stored in a container with the gas, comprising: 
 a pressure detector configured to detect pressure of the gas within the container and to generate a pressure signal in response thereto;    a gas supply line defined by a first end configured to be placed in fluid communication with a pressurized source gas, and a second end configured to be connected to the container;    a source gas control valve disposed within the gas supply line; and    a controller configured to receive the pressure signal, to determine when fluid is removed from the container, and, when the controller determines that fluid is removed from the container, to operate the source gas control valve to establish the pressure of the gas within the container to essentially the same pressure as the received pressure signal at a time prior to determining that fluid has been removed from the container.    
     
     
         8 . The system of  claim 7 , and wherein the pressure detector is connected to the gas supply line between the gas control valve and the second end of the gas supply line.  
     
     
         9 . The system  claim 7 , and wherein, when the container is configured to be connected to a liquid outlet valve to allow liquid to be removed from the container, the system further comprising a liquid outlet valve detector configured to detect actuation of the liquid outlet valve and to generate an outlet valve actuation signal in response thereto, and wherein the controller is further configured to receive the outlet valve actuation signal and to use the outlet valve actuation signal to determine that fluid has been removed from the container.  
     
     
         10 . The system  claim 7 , and further comprising a source gas connection detector configured to detect when the gas supply line is connected to a container, and to generate a gas supply connection signal in response thereto, and wherein the controller is further configured to receive the gas supply connection signal and to use the gas supply connection signal to determine that fluid has been removed from the container.  
     
     
         11 . The system  claim 7 , and wherein the controller comprises a readable memory device configured to store a plurality of pressure signals generated by the pressure detector.  
     
     
         12 . The system  claim 11 , and wherein the controller is further configured to: 
 store the plurality of pressure signals in the memory device as a function of time; and    detect a reduction in the pressure signals over a selected period of time, and to determine that fluid has been removed from the container when the reduction in the pressure signals exceeds a preselected value.    
     
     
         13 . The system  claim 12 , and wherein the controller is further configured to determine, when the controller detects that the reduction in the pressure signals exceeds the preselected value, the highest value of the stored pressure signals, and to use the highest value as the received pressure signal to establish the pressure of the gas within the container.  
     
     
         14 . A method of maintaining an equilibrium pressure between a gas and a liquid within a container, comprising: 
 providing a container having a fluid comprising a liquid and a gas in equilibrium;    determining when fluid is removed from the container; and    adding a quantity of a make-up gas to the container when it has been determined that fluid has been removed from the container.    
     
     
         15 . The method of  claim 14 , and further comprising: 
 determining a pressure of the gas in the container at a first time, the first time being prior to a time when it has been determined that fluid has been removed from the container; and    wherein the make-up gas is added to the container until the pressure of the gas in the container is approximately equal to the pressure of the gas at the first time.    
     
     
         16 . The method of  claim 14 , and wherein determining when fluid is removed from the container is performed when the container is connected to a gas supply line.  
     
     
         17 . The method of  claim 14 , and wherein determining when fluid is removed from the container is performed when a portion of the liquid flows out of the container.  
     
     
         18 . The method of  claim 14 , and further comprising: 
 determining a temperature of the liquid in the container at a first time, the first time being prior to a time when it has been determined that fluid has been removed from the container; and    determining the quantity of the make-up gas to add to the container as a function of the first temperature.    
     
     
         19 . A method of maintaining an equilibrium pressure between a gas and a liquid within a container, comprising: 
 providing a container having a fluid comprising a liquid and a gas in equilibrium;    determining when fluid is removed from the container;    measuring a pressure of the gas in the container at about the time it has been determined that fluid has been removed from the container; and    adding a make-up gas to the container until the pressure in the container is approximately equal to the measured pressure.    
     
     
         20 . The method of  claim 19 , and wherein the pressure of the gas is measured in the container at a first time prior to the time it has been determined that fluid has been removed from the container.  
     
     
         21 . The method of  claim 19 , and wherein: 
 the pressure of the gas is measured in the container at a first time prior to the time it has been determined that fluid has been removed from the container;    the pressure of the gas is measured in the container at a second time, the second time being after the first time;    determining a difference between the pressure at the first time and the pressure at the second time; and    when the difference exceeds a preselected amount, adding the make-up gas to the container.    
     
     
         22 . The method of  claim 21 , and wherein the second time is selected to be not more than ten seconds after the first time.