Abstract:
A gas cylinder for the storage of compressed gas includes a shut-off valve in engagement with a mouth of the cylinder; an external pressure sensor device for sensing pressure in the cylinder, the pressure sensor device being in continuous communication with the interior of the cylinder; a temperature sensor device for sensing temperature of the gas in the cylinder, the temperature sensor device being in thermal communication with the interior of the cylinder; a programmable computing device for calculating information from the temperature and pressure signals concerning the amount of contents in the cylinder; and a display screen operatively associated with the programmable computing device for displaying said information.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a pressure vessel for storing a compressed gas. 
         [0002]    The term “gas” as used herein includes within its scope a gas mixture. The gas may be a permanent gas, in which case it can be stored in a pressure vessel entirely in gaseous state, or a non-permanent gas, in which case it may exist under pressure in the storage vessel as a liquid phase in equilibrium with a gaseous phase according to the storage pressure. 
       BACKGROUND OF THE INVENTION 
       [0003]    Pressure vessels for storing compressed gases are of course very well known and are commonly referred to as “gas cylinders” because they conventionally, but not necessarily, have a cylindrical shape. A gas cylinder is typically able to store gas at a pressure of up to 200 bar or 300 bar. A gas cylinder is conventionally formed as a one-piece vessel, symmetrical about a longitudinal axis, from a suitable steel. The walls of the vessel have a suitable thickness to be able to withstand cycling of pressure from atmospheric pressure to a maximum storage pressure, which as stated above may be as high as 300 bar. The cylinder has an axial opening in which is fitted a valve, typically having a brass body with external screw threads that engage complementary screw threads in the mouth of the cylinder. There are various different kinds of cylinder valve, but all kinds are able to be opened to permit the controlled discharge of gas from the cylinder and also, when the cylinder is empty, to enable it to be refilled. Some cylinder valves have an integral pressure regulator to enable the user to set the pressure at which gas is delivered. Alternatively the cylinder valve may have a port in which a separate pressure regulator may be docked. The pressure regulator may include a pressure gauge to indicate the delivery pressure to a user. Such a pressure gauge is not in continuous communication with the interior of the cylinder. 
         [0004]    The traditional steel gas cylinder is heavy and can be awkward to handle. Lighter weight alternatives are known and are increasingly being used, particularly for the storage of medical gases. A lightweight gas cylinder comprises an inner vessel, sometimes known as a liner, which is reinforced with suitable fibrous material, for example, carbon fibre, and which is encased in an outer plastics shell. The inner vessel is typically made of steel, but because of the fibre reinforcement, has a smaller wall thickness than the traditional steel gas cylinder. The inner vessel is typically formed in two pieces which are welded together. 
         [0005]    It is a feature of both the traditional steel gas cylinder and its lightweight alternative, that when not in use, there is no simple way of telling how full or how empty it is, the mass of the gas in even a full cylinder being small or negligible in comparison with the mass of the cylinder itself. 
       SUMMARY OF THE INVENTION 
       [0006]    According to the present invention there is provided a pressure vessel apparatus for the storage of compressed gas, comprising: 
         [0000]    (a) a pressure vessel for containing the compressed gas;
 
(b) a shut-off valve in engagement with the mouth of the pressure vessel;
 
(c) an external pressure sensor device for sensing the pressure in the vessel, the pressure sensor device being in continuous communication with the interior of the pressure vessel and being adapted to generate a first signal which is a function of the sensed pressure in the pressure vessel;
 
(d) a temperature sensor device for sensing the temperature of the gas in the vessel, the temperature sensor device being in thermal communication with the interior of the pressure vessel and being adapted to generate a second signal which is a function of the sensed temperature of the gas;
 
(e) a programmable computing device for calculating information concerning the amount of contents in the pressure vessel from the said first and second signals;
 
(f) a display screen operatively associated with the computing device for displaying said information.
 
         [0007]    The apparatus according to the invention is thus on simple inspection of the display screen able to impart to the viewer information about the amount of contents present in the vessel. In the example of a permanent gas, the computing device may be programmed to calculate the mass of gas in the cylinder from the real gas equation. This calculated mass may be compared with the mass of gas in the pressure vessel when full, and a pictorial, graphical or digital display of the information may be made, for example as a position on a full to empty scale. 
         [0008]    If the gas is not permanent, and a liquid phase is present in the pressure vessel, the apparatus according to the invention may additionally comprise a level detector for detecting the level of liquid in the pressure vessel, the level detector being adapted to generate a signal which is a function of the sensed level of the liquid in the pressure vessel and to transmit the signal to the programmable computing device. 
         [0009]    The pressure vessel may be a lightweight vessel comprising an inner fibre-reinforced or fibre-wrapped liner and an outer plastics shell encasing the liner. The pressure vessel may, however, be a conventional steel or aluminium gas cylinder or be made of a seamless composite material. 
         [0010]    The display screen, in a lightweight vessel, is preferably set back within the plastics shell. In one embodiment, the shell has a pair of vertical integral handles and the screen has a position under a chosen one of the handles such that it is protected by the chosen handle from impacts from above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    A pressure vessel apparatus according to the invention will now be described by way of example with reference to the accompanying drawings, in which: 
           [0012]      FIG. 1  is a schematic, partially exploded, perspective view of a pressure vessel according to the invention; 
           [0013]      FIG. 2  is a schematic perspective view of a top portion of the vessel shown in  FIG. 1 ; 
           [0014]      FIG. 3  is a schematic sectional elevation of part of a wall of the pressure vessel in  FIG. 1  illustrating the pressure sensor and the temperature sensor of the apparatus according to the invention; 
           [0015]      FIG. 4  is a schematic diagram illustrating the electrical components included in the vessel of  FIG. 1 . 
       
    
    
       [0016]    The drawings are not to scale. 
       DETAILED DESCRIPTION 
       [0017]    Referring to  FIG. 1 , a lightweight gas cylinder or pressure vessel comprises an inner liner  2  wrapped or otherwise reinforced with suitable fibres  4 , for example, carbon fibres or fibres of a suitable synthetic material. The liner  2  is typically formed of a suitable steel. The liner  2  is enclosed within an outer plastics shell  6  comprising a bucket  8  and a lid  10 . The liner  2  is of generally cylindrical shape and is symmetrical about its longitudinal axis. It has a mouth  12  which is typically formed with internal screw threads (not shown) that engage a cylinder valve  14  of a kind having a handwheel  16 . The mouth  12  may be provided by a sleeve which is welded to the walls of a complementary port at the top of the liner  2 . The cylinder valve  14  has a body with external screw-threads complementary to those in the mouth  12  of the cylinder so as to enable a fluid-tight engagement to be made between the mouth  12  of the cylinder and the valve  14 . In general, the pressure vessel may be of the same kind and be made in the same way as the pressure vessel that is the subject of U.S. Pat. No. 6,386,384. 
         [0018]    As better shown in  FIG. 2 , the lid  10  of the shell  6  comprises handles  18  and  20  so as to facilitate manual lifting of the pressure vessel. The lid  10  is secured to the bucket  8  and houses a digital display screen device  22  underneath the handle  18 . The handle  18  is still able to protect the screen  22  from accidental impacts from above. The display screen device  22  is operatively associated with an external pressure sensor device  24  and an external temperature sensor device  26 , as is illustrated in  FIG. 3 . 
         [0019]    Referring now to  FIG. 3 , a shoulder position  28  of the liner  2  is formed with a first non-axial sensing port  30  therethrough. The sensing port  30  receives in fluid-tight engagement therewith the pressure sensor device  24 . In an alternative arrangement (not shown) the port  30  is formed through the mouth  12  of the liner on the vessel side of the cylinder valve  14 . 
         [0020]    The pressure sensor device  24  is preferably of a kind based on the flexure of a ceramic membrane, for example, of aluminium oxide. This material has good elasticity and is almost free of hysteresis. The upper side of the membrane has a bridge arrangement (not shown) of electric resistors attached thereto. Flexure of the membrane in response to the pressure in the pressure vessel causes the resistors to be deformed with the result that their electrical resistivity varies. An input voltage is applied to the bridge and an output voltage dependent on the degree of flexure of the membrane and hence the pressure in the pressure vessel is tapped off from the bridge in a known manner. The output voltage is conducted to associated electrical circuits which amplify the voltage and provide a signal representative of the pressure to the display screen device  22 . The pressure sensor device  24  is generally similar to that disclosed in U.S. Pat. No. 6,978,678 to which document the reader is referred for further information. 
         [0021]    Referring again to  FIG. 3 , the shoulder portion  28  of the liner  2  also has a second non-axial sensing port  32  therethrough. The sensing port  32  receives the temperature sensor device  26  in fluid-tight engagement therewith. The temperature sensor device  26  may include a sleeve  34  containing a thermocouple  36 . The sleeve  34  may depend from a plug  38  which engages the port  32 . The thermocouple leads may extend through the plug  38  to associated electrical circuits (not shown) at the proximal end of the plug which amplify the electrical signal generated by the thermocouple  36  the size of which electrical signal is dependent upon the gas temperature within the pressure vessel. Electrical leads (not shown) from the plug  38  may extend between the liner  2  and the lid  10  of the shell  6 . 
         [0022]    In an alternative arrangement (not shown) to that shown in  FIG. 3 , the second port  32  may be formed not adjacent to the first port  30  but instead in the opposite shoulder of the liner  2 . In this case, electrical leads from the temperature sensor device  26  to the display screen device  22  may be housed between the liner  2  and the lid  10  of the shell  6 . 
         [0023]    If the gas is a permanent gas, the mass of the gas can be calculated from a knowledge of the sensed pressure, sensed temperature, the volume of the pressure vessel, and the composition of the gas with which the cylinder or pressure vessel is filled. If the gas is not a permanent gas, however, and if the part of the gas is present in the pressure vessel in the liquid phase, then performance of such a calculation requires a knowledge of the volume of liquid present. In such an example, the temperature sensor device  26  may also incorporate a level sensor or level sensors (not shown). Thus, the plug  38  may receive leads from a thermistor (not shown) which is used to sense the level of the liquid in the cylinder or pressure vessel. Alternative level sensing devices can be used, for example, one emphasizing sonic sensing of the liquid level. 
         [0024]    The display screen device  22  includes a programmable computing device  40  for calculating the mass of gas in the pressure vessel from the sensed pressure and temperature signals (and, as appropriate, the liquid level) and for feeding signals representing the results of the calculations to the screen  42  of the screen device  22 . The screen  42  typically utilises light emitting diodes (LEDs) and/or a Liquid Crystal Display (not shown). The display screen device  22  may also house a battery (not shown) for activating the display screen  42 . The battery may be disposable or rechargeable and may also be used to provide electrical power to the sensors. 
         [0025]    The computing device  40  may also calculate parameters relating to the mass of gas in the cylinder or pressure vessel. For example, the device  40  may be programmed with the mass of gas present when the cylinder was full, and calculate how full the cylinder is at any time, for example, on a scale of 0-100, 0 being empty and 100 being full. This information can be displayed numerically as a percentage as indicated by the reference numeral  46  in  FIG. 2  or pictorially as indicated by the reference numeral  48 . Other calculations may be made. For example, if the gas is intended for use as a shielding gas in electric arc welding, then there may be calculated and displayed the length of time for which gas can be drawn from the cylinder before it runs out. In another example, if the gas is intended for use in filling balloons, the mass of gas present in the cylinder at any one time may be expressed in terms of the number of balloons that can be filled before the cylinder runs out of gas. 
         [0026]    The display screen  42  may be permanently illuminated or may be provided with control buttons  50  such that a particular parameter or parameters will be displayed only when the buttons  50  are depressed. 
         [0027]    The electrical arrangements are illustrated schematically in  FIG. 4 . All requirements for electrical power are met from a rechargeable or disposable electrical DC battery  60 . The battery supplies the electrical power necessary to operate the pressure sensor device  24  and the temperature sensor device  26 . The battery  60  also provides the necessary electrical power to operate the display screen device  22 . The display screen device  22  includes an analogue to digital converter circuit  62  which converts signals from the sensors  24  to  26  into digital form. The converter circuit  62  is operatively associated with a programmable microprocessor  64  including a RAM (Random Access Memory) device (not shown) and interposes with an input keyboard  66  and output devices including a liquid crystal display screen  42 , a Light Emitting Diode display  68  for providing a visual alarm signal and a buzzer  70  for making an audible alarm signal. The voltage provided by the battery  60  may be transformed into a first larger DC voltage by transformer  72  so as to provide electrical power to the sensors  24  and  26  and the analogue-to-digital converter  62 , and to a second larger DC voltage by transformer  74  so as to provide electrical power to the microprocessor  64  and the output devices. 
         [0028]    The pressure vessel apparatus according to the invention is thus able to give the user of a cylinder a visual indication of its contents, that is how full it is, on demand at any time. 
         [0029]    Various changes and alterations may be made to the apparatus shown in the drawings. For example, it is not necessary to locate the sensing ports in the shoulder of the pressure vessel. An alternative is to provide a shut off valve assembly (or main cylinder valve) which includes the sensing port or ports on the pressure side of the main cylinder valve. The display screen device may also be incorporated in the valve assembly or in any guard for the valve, or may still be positioned on the lid  10  of the shell  6 .