Abstract:
A tap ( 10 ) for a gas cylinder has a non-sealing gate valve ( 44 ) positioned between an on/off valve ( 14 ) and a pressure reducer ( 18 ) of the tap. The gate valve ( 44 ) is normally in a position with a normal passage area. When the valve ( 14 ) is opened the gate valve ( 44 ) is rapidly moved by the pressurized gas towards a position with a limited passage area in order to reduce the shock wave applied to the pressure reducer ( 18 ). After the pressures on both sides of the gate valve ( 44 ) have been balanced, the gate valve returns to its position with a normal passage area.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not Applicable  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable  
       BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates to a tap for a gas cylinder, comprising a tap body having a gas passage formed in the tap body, an on/off valve and an pressure reducer attached to the tap body, the valve being openable to allow the gas to flow out in venting mode through the said passage towards the pressure reducer, and a means for limiting the shock wave when the valve is opened, this means being positioned between the valve and the pressure reducer.  
         [0004]     The velocities encountered in a tap for a gas cylinder at high pressure (more than 200 bar) are very high. For gases such as helium, the velocities can generally exceed the speed of sound. With such rates, some seats or plastics pads of pressure reducers cannot withstand the adiabatic shock and may burn in the presence of an oxidizing gas. It is therefore necessary to limit the pressure and reduce the gas velocity in order to absorb the shock wave when the main valve of the tap is opened to vent the gas. In the prior art, filters were provided between the main valve and the pressure reducer, but these filters have the disadvantage of interfering with the flow of gas when the cylinder is almost empty. Moreover, the filters may become clogged. They are consequently subject to shocks on each opening and may generate particles. With a high pressure, which may be of the order of 300 bar, in other words if the gas cylinder is full, known filters do not cause any problems and do not interfere with the flow. However, the filters cause a constant pressure drop, and at a low pressure, of less than 50 bar, perturbations commence and become worse at 10 bar. These known filters creating a constant pressure drop therefore alter with the gas expansion curve at low pressure.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     The object of the invention is therefore to overcome this drawback and to provide a tap for a gas cylinder with a means for preventing the adiabatic shock without altering the gas expansion curve.  
         [0006]     To achieve this object of the invention, the tap for a gas cylinder of the aforementioned type is characterized in that the means for limiting the shock wave comprises a movable gate valve positioned in the said gas passage, this gate valve being forced, when the valve is opened, by the effect of the shock wave from a first position in which there is a normal passage area to a second, non-sealing position with a limited passage area to reduce the shock wave, the said gate valve returning to its first position with a normal passage area after the gas pressure has been established on both sides of the gate valve.  
         [0007]     The gate valve is normally in the open position, in other words the position with a normal passage area, and when the main tap is opened the gate valve is instantly pushed by the velocity and pressure of the gas towards its second, non-sealing position which limits the gas passage area in order to limit or absorb the shock wave or the adiabatic shock. In this second position, a small aperture having a passage area which is large enough to avoid interference with the flow at low pressure remains open, and after the balancing of the pressures the gate valve returns to its position with the larger passage area, as a result of which the system according to the invention can provide a variable pressure drop, unlike the constant pressure drop created by known filters. In the system according to the invention, the filter can be placed in the tail of the tap (inlet or conical connector) which has a larger area, thus avoiding shocks to the filter. The system according to the invention is very useful for applications using oxidizing gases, in other words oxygen, but also has advantages which should not be overlooked for applications using neutral or any other gases. The system is particularly suitable for oxygen applications at more than 200 bar. The invention enables user security to be enhanced by avoiding dangerous phenomena. The system according to the invention is particularly advantageous for oxygen therapy.  
         [0008]     The system is useful for taps with incorporated piston-type pressure reducers having a gate valve in the low pressure area which is normally open, but it can be applied to other technologies. For example, the system can also be used with a pressure reducer having a gate valve in the high pressure area in a normally closed or open position. In another embodiment, the system according to the invention can be used in an assembly with a standard or conventional tap provided with an on/off valve linked by a duct to a pressure reducer. In this case, the adiabatic compression prevention system would be located in the duct immediately before the pressure reducer seat. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0009]     The invention will now be explained in greater detail with reference to the attached drawings, in which:  
         [0010]      FIG. 1  shows a tap for a gas cylinder with an incorporated pressure reducer and with the adiabatic compression prevention system according to the invention, the main on/off valve being in the closed position, and the gate valve of the adiabatic compression prevention system being in the first position with a normal passage area;  
         [0011]      FIG. 2  is a view similar to that of  FIG. 1  but with the main valve in the open position and the gate valve of the adiabatic compression prevention system in the second position which limits the gas passage area;  
         [0012]      FIG. 3  shows the adiabatic compression prevention system (detail X) of  FIG. 1 , on an enlarged scale, with the gate valve in its position with a normal passage area which it occupies when the main valve of the tap is closed or if the main valve of the tap is opened after the gas pressure has been balanced on both sides of the gate valve;  
         [0013]      FIG. 4  is a view similar to that of  FIG. 3 , but shows the detail Z of  FIG. 2 , on an enlarged scale, in other words with the gate valve in its position which limits the gas passage area; and  
         [0014]      FIG. 5  shows the expansion curve for a tap according to the prior art and a tap with the system according to the invention.  
     
    
       [0015]     Corresponding reference numerals will be used throughout the several figures of the drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0016]      FIGS. 1 and 2  show a tap  10  for a gas cylinder according to the present invention, comprising a tap body  12 , a main on/off valve  14 , a filling valve  16  and an incorporated pressure reducer  18 . A gas passage  20  extends from the lower end  22  of the tap body  12 , for connection to the gas cylinder (not shown), to the incorporated pressure reducer  18 . This gas passage  20  is commonly called the high-pressure section of the tap  10 .  
         [0017]     The gas passage  20  has a first part  20   a  extending obliquely upwards from the lower end of the tap body  12  and communicating with a first transverse part  20   b  which opens into a first transverse cavity  24  which, in turn, communicates with a second transverse part  20   c  of the gas passage  20  which, in turn, opens into a second transverse cavity  26 . The gas passage also comprises a vertical part  20   d  which communicates with the second transverse part  20   c  and which has a vertical counter-bore  28 , shown most clearly in  FIGS. 3 and 4 , and in which the adiabatic compression prevention system  30  according to the invention is placed (details X and Z of  FIGS. 1 and 2 ). The adiabatic compression prevention system  30  is located in the bore  28  immediately below the piston  32  of the pressure reducer  18  which is connected to the upper end of the tap body  12  and which is known in the prior art.  
         [0018]     The main valve  14  is also known in the prior art and will therefore not be described in detail here. It will simply be mentioned that this main valve  14  is provided with a sealing ring  34  engaging an annular seat  36  to form a seal at the bottom of the first transverse cavity  24  when the main valve  14  is closed. In the open position of the main valve  14 , the sealing ring  34  is disengaged from the annular seat  36 . The filling valve  16  is also known in the prior art and will therefore not be described in detail here. A filter  38  is located at the lower end of the first oblique part  20   a  of the gas passage  20 . The piston  32  of the pressure reducer  18  is provided at its lower end with a pad  40  of plastics material which interacts with a fixed aperture  42  of the seat of the pressure reducer  46  (see  FIGS. 3 and 4 ), to regulate the gas pressure.  
         [0019]     The adiabatic compression prevention system  30 , which will now be described with reference to  FIGS. 3 and 4 , comprises two parts  44  and  46 , one being fitted into the other. The first part  44 , in other words the lower part, is a gate valve  44  which is movable vertically in the vertical counter-bore  28 , and the other, upper part  46 , in other words the seat  46  of the pressure reducer  18 , is received in a threaded housing  48  in the counter-bore  28 .  
         [0020]     A sealing ring  50  is positioned between the fixed seat  46  and the tap body  12 . The fixed seat  46  is provided with a plurality of recesses  52  formed in its upper surface for the engagement of a tightening tool for the purpose of fixing the seat  46  in the counter-bore  28  of the tap body  12 . A vertical gas passage  54  extends from one end to the other through the two parts  44  and  46  of the adiabatic compression prevention system  30 . This vertical passage  54  comprises, at the upper end of the seat  46 , the fixed aperture  42  interacting with the pad  40  of the piston  32  of the pressure reducer  18 , for the purpose of regulating the gas pressure. The vertical passage  54  also comprises a central aperture  56  passing axially through the gate valve  44  and keeping the forward and downstream end of the gate valve  44  in constant communication. This aperture  56  forms the limited passage area. The movable gate valve  44  located at the upstream end of the fixed seat  46  is also provided with a vertical annular guide part  60  extending upwards from the lower head end  58  of the gate valve  44  and received slidably in a vertical bore  62  of the seat  46  of the pressure reducer  18 .  
         [0021]     One or more radial cut-outs or openings, for example holes  64 , are formed in the vertical guide part  60  of the gate valve  44 . These openings  64  extend radially through the wall of the guide part  60  to open in a bore  66  formed inside the movable gate valve  44 . The central aperture  56  of the gate valve  44  is also in communication with the bore  66 . The bore  66  is in constant communication with the bore  62  of the seat  46 , and the bore  62  is in constant communication with the aperture  42 .  
         [0022]     In the first position of the gate valve  44  with a normal passage area, these radial openings  64  open into the space of the counter-bore  28  surrounding the gate valve  44  and form part of a passage by-passing the central aperture  56  and extending around the outside of the gate valve  44  in the counter-bore  28 , to put the upstream end of the gate valve  44 , in other words the part  20   d  of the gas passage  20 , in communication with the downstream end of the gate valve  44 , in other words the downstream end of the central aperture  56  of the gate valve  44  of the adiabatic compression prevention system  30 .  
         [0023]     A compression spring  69  is provided inside the two parts  44  and  46  and bears with its upper end on an upper surface of the bore  62  of the seat  46  of the pressure reducer  18  and with its lower end on a bottom surface of the bore  66  of the gate valve  44 , so that the movable gate valve  44  is normally pushed downwards towards its first position of engagement with a bottom surface  28   a  of the counter-bore  28  of the tap body  12 , around the part  20   d  of the gas passage  20  opening into the counter-bore  28 .  
         [0024]     The head part  58  of the gate valve  44  is provided at its upper end with a radial shoulder forming an annular bearing surface  68  which can contact an annular surface  70  forming a counter-bearing surface at the lower end of the seat  46  of the pressure reducer  18 .  
         [0025]     The external diameter of the head part  58  of the movable gate valve  44  is smaller than the diameter of the internal circumferential surface, which surrounds it, of the counter-bore  28 , and the openings  64  are formed in the vertical guide part  60  between the radial shoulder  68  and the upper end of the guide part  60 .  
         [0026]     At the lower end of the head part  58  of the movable gate valve  44 , on its radial surface opposite the seat  46  of the pressure reducer  18 , there are provided appropriate means  72  such as spacers, ribs or grooves forming at least one radial passage, or any other appropriate means to ensure that the movable gate valve  44  cannot be engaged in a sealed way with the bottom surface  28   a  of the bore  28  of the tap body  12 , in such a way that in the lower position (first position) of the gate valve  44 , shown in  FIG. 3 , the part  20   d  of the gas passage  20  is in communication with the downstream end of the gate valve  44  (the downstream end of the central aperture  56 ) through the space of the counter-bore  28  surrounding the gate valve  44  and through the radial openings  64  (forming the normal passage area), and also through the central aperture  56  forming the limited passage area.  
         [0027]     Conversely, in the upper position (second position) of the movable gate valve  44 , in other words its position with a limited passage area as shown in  FIG. 4 , the movable gate valve  44  is moved upwards in such a way that its annular bearing surface  68  is in contact with the counter-bearing surface  70  of the fixed seat  46  of the pressure reducer  18 , and the guide part  60  with its radial openings  64  is received completely inside the bore  62  of the fixed seat  46 . The openings  64  are therefore blocked or closed, and the gas can no longer penetrate from the counter-bore  28  through these openings  64  into the adiabatic compression prevention system  30 . Consequently, the gas at high pressure can pass through the adiabatic compression prevention system  30  only via the limited small central aperture  56 , and the adiabatic shock applied to the pad  40  of the movable piston  32  of the pressure reducer  10  is limited.  
         [0028]     It should also be noted that the gas escaping through the aperture  42  of the fixed seat  46  flows upwards in an annular passage surrounding the lower end of the piston  32  of the pressure reducer  18 , then passes to the inside of the piston  32  and leaves the piston at its upper end.  
         [0029]     If the pressure on the upper end of the piston  32  becomes too great, the piston  32  is forced downwards against the force of the helical spring  74  ( FIGS. 1 and 2 ), thus reducing the space between the aperture  42  of the fixed seat  46  and the pad  40  of the piston  32 . A safety valve  76  surrounds the piston  32  of the pressure reducer  18 . If the pressure below this safety valve  76  becomes too high, the safety valve  76  is moved vertically upwards against the force of the spring and the gas can escape through the radial holes  78 .  
         [0030]     The adiabatic compression prevention system  30  is normally in the position of  FIG. 3  when the main tap  14  is closed. In this case, the movable gate valve  44  is pushed downwards by the spring  69  and engages with the bottom surface  28   a  of the counter-bore  28  of the body  12  of the tap  10  around the part  20   d  of the gas passage  20 .  
         [0031]     When the tap  14  is opened, the gas under high pressure flows in at high velocity through the part  20   d  of the passage  20  and forces the movable gate valve  44  upwards against the action of the spring  69  thus moving the gate valve  44  towards its upper position in which the openings  64  are positioned inside the fixed seat  46  of the pressure reducer  18  and are therefore no longer in communication with the space of the counter-bore  28  surrounding the movable gate valve  44 . The gas under pressure can pass through the adiabatic compression prevention system  30  only via the aperture  56  with minimal passage area formed in the gate valve  44 , which is in constant communication with the upstream and downstream ends of the gate valve  44 .  
         [0032]     When the gas pressure has been established on both sides of the movable gate valve  44 , the spring  69  can again push the movable gate valve  44  downwards into contact with the bottom surface  28   a  of the counter-bore  28  (the position of  FIG. 3 ). In this position, a normal, enlarged passage area is provided for the gas under pressure, which can now by-pass the central aperture  56  and pass from the part  20   d  of the gas passage  20  into the radial passage  72 , flowing in an outward radial direction into this passage, and can then flow upwards in the counter-bore  28  around the lower head part  58  of the gate valve  44  and finally inwards through the radial openings  64  to enter the vertical passage  54  and finally escape through the aperture  42  located in the proximity of the pad  40  of the piston  32  of the pressure reducer  18 .  
         [0033]     Thus, when the main tap  14  is opened, the adiabatic compression prevention system  30  limits the flow and velocity of the gas to protect the pressure reducer, by providing a limited passage area for the gas under pressure, and, when the gas pressure has been established on both sides of the gate valve, the gate valve is moved to an open position, providing a normal passage area which is larger (by a factor of two to five) for the gas under pressure. By comparison with the filters (having a particle size or porosity of approximately 20 um) known in the prior art, the adiabatic compression prevention system according to the present invention provides a variable passage area for the gas under pressure, in other words a limited passage area on the opening of the main valve and a normal, larger passage area after the gas pressure has been established on both sides of the gate valve. Thus the system according to the invention is a variable pressure drop system. It should be noted that the resistance to the passage of the gas under pressure through the central aperture  56  is lower than the resistance to the passage of the gas through the known filters of the prior art, and therefore the system according to the present invention affects the expansion curve less than the known filters, as shown in  FIG. 5 , but provides the same protection against adiabatic shock as the known filters. As shown in  FIG. 5 , in the system according to the invention the desired regulated pressure P 2  can be maintained for longer when the pressure P 1  in the cylinder decreases and the cylinder is almost empty. In other words, the quality of the flow curves will be better than with the conventional system (or with a filter).  
         [0034]     The invention is not limited to the particular embodiments shown in the drawings, and various modifications can be made without departing from the scope of the attached claims. For example, the circular cut-outs or openings  64  could be replaced with elongate cut-outs extending to the upper end of the vertical guide part  60 . Also, instead of the openings  64  formed in the gate valve  44 , it would be possible to provide cut-outs formed by grooves in the seat  46  of the pressure reducer  18  which would be blocked by the vertical guide part  60  of the gate valve when it was received in the fixed seat  46 . Additionally, instead of being guided in the fixed seat  46 , the gate valve  44  could have vertical ribs on its outer circumference, spaced apart in the circumferential direction and guided on the inner circumferential surface of the counter-bore  28 . In this case, the normal passage by-passing the central aperture  56  of the gate valve  44  would be made to communicate with the downstream end of the central aperture  56  of the gate valve  44  via an annular passage opened between the bearing surface  68  and the counter-bearing surface  70  when the gate valve  44  is pushed downwards by the spring  68  towards its first position with a normal passage area. Furthermore, instead of forming one or more radial passages  72  in the upstream surface of the gate valve  44 , this surface can be smooth and passages or grooves can be formed in the bottom surface  28   a  of the counter-bore  28 . Other modifications are possible and can be provided by persons skilled in the art if necessary.