Abstract:
A thermal safety device for cutting off gas pipelines, wherein gas transfer is prevented by the safety device when temperature increases in the section of the gas pipeline placed downstream from the safety device, especially when connected gas apparatuses are in a closed position maintains production costs and dimensions at a level as low as possible. The safety device includes a check valve which prevents backflow from the gas pipeline which is placed downstream from the device. The inventive device also includes a pressure sensitive element placed downstream from the safety device which is actuated by the pressure in the pipeline. The pressure sensitive element is coupled to a cut-off valve in such a way that when pressure increases in the downstream pipeline the valve prevents gas from flowing into the pipeline.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention relates to a safety device for cutting off gas pipelines when temperature increases in an unacceptable way according to the preamble of the first patent claim. 
     Such thermal valve safety devices that are employed in pipelines, such as upstream from gas apparatuses, gas meters, etc., are available in a large variety of designs. They are used to interrupt gas supply before temperature increases at the aforementioned gas apparatuses to such level that their external tightness is jeopardised. 
     EP 118 152 A1 describes a valve in which a ball is kept respectively in open and, after reaching a limit temperature in closed position both by a spring and also by an alloy with thermal shape memory, with the spring being in such shape that automatic opening is impossible after closing. 
     The disadvantage of this solution is that the component of an alloy with thermal shape memory, located in the housing interior, has to be subjected to the higher temperature in order to achieve the desired closing of the valve. This means that the entire valve has to be heated in order to attain a response of the thermo-sensitive part by conduction of said heat. And it is necessary to place such valve immediately adjacent to each component that is jeopardised by temperature increase in order to detect the temperature in the area and, if need be, cut off the gas pipeline. 
     EP 343 615 A1 describes a valve with a cone as cut-off element. In this solution a guide rod is led through a valve cover and connects said plug with a fuse body that is pre-tensioned against the cover by means of a pressure spring. Softening of the fuse body removes the guide rod from the former so that, under the impact of the pressure spring, the plug can move abruptly in the closing direction. 
     Also this solution has the disadvantage that, on the one hand, the thermo-sensitive element is positioned in the housing interior and, hence, also the entire valve has to be heated and, on the other, such a valve has to be placed directly adjacent to each component that is jeopardised by temperature increase. 
     A thermal safety valve is also known from the utility model DE 94 20 607. This thermal safety valve is essentially of the same construction as the solution described above, i.e. the housing is provided with a soft solder which keeps a cut-off element, in this case a valve cone, in open position. Additionally a heating jacket, which is preferably electrically heatable, is provided at the valve housing in the area of the internal soft solder, so that the safety valve does not only actuate automatically after the soft solder is directly subjected to the higher temperature but which also facilitates its remote actuation. 
     The disadvantage of this solution is, that besides its complicated construction, it is necessary to provide additionally a source of auxiliary energy, piping and respective actuation elements. 
     EP 637 457 A1 describes an automatic closing device for a shut-off device. The element inhibiting the closing force has at least one pressure-actuated hollow body with a variable volume with a rated breaking point of a material whose melting temperature is adjusted to a defined limit value temperature. Upon achieving or exceeding said limit value temperature the closing operation is triggered by melting of the breaking point material and a subsequent pressure relief. The force of pressure in the hollow body is reduced and the closing force is activated. The rated breaking point can be executed as a reaction line that can be laid at any distance from the shut-off device so that a fire occurring in the reaction line yet at a distance from the shut-off device triggers the closing action. 
     The disadvantage of the latter solution is that the reaction line has to cover the entire area of the unit to be protected which, particularly in case of large units, entails disproportionately high costs. 
     DE 296 12 921 U1 describes a cut-off device for a gas pipeline system with a cut-off element that is kept in open position by at least one closing force-inhibiting element. The element has at least one pressure-actuated hollow body with a variable volume that is connected to a so-called function line consisting of a material whose melting temperature is adjusted to a defined limit value temperature. Melting of the function line causes a pressure drop in the hollow body and the closing force actuates the cut-off element so that the cut-off device is closed and the flow through the pipeline is discontinued. The pipeline outlet is additionally provided with a backflow check valve which, upon a pressure drop in the pipeline, prevents a gas backflow from the downstream pipeline. 
     In this cut-off device there is a pressure in the hollow body and the function line which is required to keep the cut-off element in the open position. Said pressure, however, is independent of the pressure in the gas pipeline. 
     It is also known that so-called gas flow control valves are used to automatically cut off gas pipelines. Said gas flow control valves are used to interrupt gas supply upon increase of gas consumption beyond a defined value. 
     The disadvantage of such gas flow control valves is that, in case of a damage at the gas pipeline, e.g. by a fire, and with a closed gas apparatus the gas volume flowing from the leak will have to be larger than the gas volume flow otherwise required for the operation of the gas apparatus before the gas flow control valve is closed. 
     The invention is focusing on the issue of developing a safety device for cutting off gas pipelines of the described type wherein the gas transfer through the safety device is prevented when temperature increases in the section of said safety device placed downstream from the gas pipeline, especially when connected gas apparatuses are in a closed position. In addition, it shall be possible to avoid an excessive pressure rise in the downstream pipeline. The aim of the invention is to maintain production costs and dimensions at a level as low as possible. According to the present invention the problem is solved by providing a safety device with a check valve that prevents a backflow from the gas pipeline which is placed downstream from said device and by arranging a pressure sensitive element which is actuated by the pressure in the pipeline downstream from said safety device. Said pressure sensitive element is coupled to a cut-off valve in such a way that when pressure increases in the downstream pipeline said valve prevents gas from flowing into the pipeline. 
     Thus a solution has been found that removes the disadvantages of the prior art that a thermal element in the housing interior has to be actuated by the higher temperature in order to achieve the desired closing of the valve. It is also no longer necessary to place such valve directly adjacent to each component that is jeopardised by a temperature increase in order to detect the temperature in this area and, if need be, cut off the gas pipeline. Further distinguishing features of this solution are above all its simplicity and production dimensions. 
     Further advantageous arrangements of the invention are described in the other patent claims. In order to prevent, for instance, the pressure rise from becoming excessively high after a temperature increase in the downstream pipeline a backflow can be released from the downstream pipeline by the check valve or a by-pass circumventing said check valve, after the gas transfer into the downstream pipeline has been cut off by the cut-off valve, with the cut-off valve also releasing backflow from the downstream pipeline. 
     In order to largely simplify assembly the movable cut-off element of the check valve can be a piston or a diaphragm which is loaded by a spring and/or its own weight against the gas flow direction. The piston or diaphragm disk can simultaneously form the pressure sensitive element. 
     A particularly advantageous form of execution in terms of manufacturing and cost-effectiveness is achieved when a rising pressure in the gas pipeline placed downstream from the safety device moves the piston into a bore and a return movement of the piston is prevented by the engagement of a latching stop. The bore is sealed by a flexible sealing at the piston. 
     In order to obtain a stroke motion of the piston by an initially low friction between piston and seat already at a low pressure and simultaneously ensure tightness at rising pressure the bore is preferably tapered in the moving direction of the piston. 
     Preferably, the section of the bore that is assigned to the piston after the engagement of the latching stop has an expansion. The fact that the diameter of said expansion is larger than the diameter of the piston with flexible sealing creates a gap between piston and expansion through which the pressure in the downstream pipeline is relieved. Following said pressure relief the piston, under the impact of a spring and/or its own weight as well as the latching stop, is again outside of the expansion and its flexible sealing seals the bore. 
     A particularly simple construction in terms of manufacturing is obtained when the latching stop comprises an expansion of the bore and a flexible sealing. In this case the diameter of the expansion is smaller than that of the piston with a flexible sealing. In addition, the expansion-to-bore transition has a limit stop. 
     A further form of execution of the inventive safety device for cutting off gas pipelines is attained by coupling the pressure sensitive element to an already known gas flow control valve in such a way that the gas flow control valve is in a closed position after a pressure rise in the downstream pipeline. This can be achieved, e.g., by the pressure sensitive element releasing the lock of a pre-tensioned spring when pressure increases and the gas flow control valve is moved into its closed position by the impact of the spring. 
     Said coupling with a gas flow control valve makes it possible to safely close the downstream pipeline in an emergency case, irrespective of the operating state of the connected gas apparatus. 
     The axial movement of the piston is preferably limited on either side by a seat with the seat upstream from the piston forming the check valve together with the piston, while the seat downstream from the piston forming the gas flow control valve together with the piston. 
     In order to avoid an abrupt movement of the piston from its operating position upon switching on the gas apparatus, and thus a premature response of the gas flow control valve, the piston has, at least at one front face, an extension which slides with loose fit in a guide aperture which is gas-tight closed at the front side. Thus, the opening process is damped. 
     Further advantageous executions are obtained when the safety device has a manipulator that can be externally actuated and is used to take the spring into the pre-tensioned and locked position or/and with which the safety device in a closed position can be brought into its initial position. 
     Its is also possible to arrange a number of safety devices in a gas distributor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Below is a more detailed description of the invention by means of several practical examples. The figures show the following: 
     FIG. 1 is a sectional view of an inventive safety device with ball valve in accordance with the present invention, 
     FIG. 2 is a fragmentary sectional view of another embodiment of an inventive safety device shown in an operating position, 
     FIG. 3 is a view similar to that of FIG. 2 but showing the inventive safety device shown in a pressure compensation position, 
     FIG. 4 is another view similar to FIG. 2 but showing inventive safety device shown in a safety position, 
     FIG. 5 is another embodiment of an inventive safety device shown with a gas flow control valve, shown in an operating position, 
     FIG. 6 is a view of the embodiment shown in FIG. 5 but shown in a safety position, 
     FIG. 7 is a sectional view of a further embodiment of an inventive safety device shown with a gas flow control valve, and in a operating position, 
     FIG. 8 is a view of the embodiment of FIG. 7 shown with a gas flow control valve, and in a pressure compensation position, 
     FIG. 9 a view of the embodiment of FIGS. 7 and 8 shown in a safety position, 
     FIG. 10 is a view of the embodiment shown in FIGS. 7,  8 , and  9  but shown in a working position, 
     Fig. 11 is a view of the embodiment of FIGS. 7,  8  and  9  shown with a closed gas flow control valve, 
     FIG. 12 is a view of the embodiment of FIGS. 7,  8  and  9  but shown incorporating a manipulator. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The inventive safety device that is explained thereunder in greater detail is described in FIG. 1 on the basis of a ball valve that is known to the expert and used here as a cut-off valve  1 . The safety device comprises a tubular housing  11  with a connection at either end, in this case drawn as a thread. It goes without saying that also another connection types are possible. Next to the inlet-side internal thread a check valve  2  is centrically arranged in the housing  11 . The flow direction prevailing in the pipeline under normal operation conditions, hereinafter referred to as flow direction, is marked by an arrow. 
     The check valve  2  in this case comprises two punched disks  21 / 22  arranged behind each other in flow direction, which have at their centre a slide bearing  211 / 221  each for an axially movable tappet  23 , to which a piston  24  is fastened between the punched disks  21 / 22 . A pressure spring  25  actuates on the front face of the piston  24  opposite the gas inlet  113  whose other end is braced against the punched disk  22 . In order to ensure gas tightness of the check valve  2  in closed position an O-ring is arranged as a flexible sealing  242  in a circumferential groove  241  of the piston  24 , with the bore  26 , tapered in flow direction and made through the internal wall of housing  11 , providing the valve seat for the check valve  2 . 
     The housing  11  also comprises a ball that is used as a shut-off mechanism  12 , is pivot-borne in sealings serving as seat  16  and has a through-hole  121  in longitudinal direction of the housing  11 . A pivoting axis  14 , borne in a gastight manner on O-rings  13  and solidly connected to the tubular yoke  112  of the ball valve  1  housing  11 , which leads radially to the outside is, on the one hand, keyed to the ball  12  and, on the other, to a manipulator  15  with which the ball valve  1  can be brought into its open or closed position by means of a swivelling movement. Construction and mode of action of ball valve  1  are known to the expert, hence, there is no need for a detailed explanation here. 
     A pressure sensitive element  3  is arranged between the ball valve  1  and the check valve  2 . The pressure sensitive element  3  comprises a pot-shaped metal bellows  31  that is fixed in a gastight manner to the front face of the housing  11  internal wall and projects radially into the housing  11  interior and on whose bottom a tappet  32  is fixed whose other end is led lengthwise movable inside a through-hole  111  in the housing  11  wall. The tappet  32  supports a thrust piece  33  that projects from the housing  11  to the outside. 
     The yoke  112  bears an L-shaped lever in a pivotable manner whose one limb  341  has an aperture  342  into which the end of the thrust piece  33  projects that is led out of the housing  11 . The other limb  343  sits close to the manipulator  15  when the ball valve  3  is in open position. A torsion spring  35  is axially led on the yoke  112  whose one end is braced against the housing  11  while the other end sits close to the limb  343  so that the latter loads the manipulator  15  in the closing direction of the ball valve  1  and the thrust piece  33  forms a latch for the lever. 
     The function of the inventive safety device that is described in this first practical example is as follows: 
     In the operating position the ball  12  of the ball valve  1  is open. If the gas apparatus located at the end of the downstream gas pipeline that is not depicted is out of operation, the check valve  2  is in its closed position. If now there is a temperature increase, e.g. by fire, in the section downstream from gas pipeline the heat causes a pressure rise in said pipeline. This pressure rise effects a stroke of the metal bellows  31  which, by means of the tappet  32 , lifts the thrust piece  33  out of the through-hole  111  and hence its catch. Under the force of the tensioned torsion spring  35  the limbs  341  is not arrested any longer and hence the limb  343  and thus also the manipulator  15  are rotated into the closing direction and the ball valve  1  is closed. The safety device is in the safety position. 
     In order to prevent an excessive pressure rise in the downstream pipeline the safety device described in this practical example can have an additional bypass. A pressure control valve that is known to the expert and hence not further explained is functionally arranged in said bypass, which connects the up- and downstream pipeline while bypassing the safety device, in such a manner that it is always shut in the gas flow direction while a pressure compensation from the downstream to the upstream pipeline is possible. Said pressure control valve has to be adjusted in such a way that it responds only after a closing of the cut-off valve  1 . 
     FIGS. 2 to  4  are schematic representations of a second modified practical example of an inventive safety device which is particularly distinguished by its simple construction. This inventive safety device comprises a housing  11  with a gas inlet  113  and a gas outlet  114  depicted as a corner arrangement in this practical example. Gas inlet  113  and gas outlet  114  are each provided with a connection for a gas pipeline not depicted here. 
     The housing  11  comprises a check valve  2  consisting of a piston  24  and a bore  26  in the housing  11  which forms a valve seat that is preferably tapered in flow direction. In flow direction downstream from the bore  26  is a piston  24  which, as in the first practical example, has an O-ring in a circumferential groove  241  as a flexible sealing  242  in order to ensure the gas tightness of the check valve  2  in closed position. The piston  24  is loaded by its own weight against the flow direction. 
     In addition, the piston  24  has at one side a front face extension  243  that is led into an aperture  115  in the housing  11 . The aperture  115  is fitted with a groove  116  in which a radial spring-loaded element  117 , e.g. a wire strap, is partially borne while its remainder sits in the aperture cross-section. 
     The extension  243  has a first contraction  244  in whose area a spring-loaded element  117  is positioned in the operating position (FIG.  2 ). The limitation of the contraction  244  opposite the piston  24  forms a first limit stop  245  that limits the opening stroke of the piston  24 . By contrast the limitation of the first contraction  244  facing the piston  24  has a tapered transition  246  so that upon reaching the spring-loaded element  117  the latter expands into its groove  116  until a second contraction  247  arranged on the shaft  243  between piston  24  and first contraction  244  catches. By contrast the limitation of the second contraction  247  facing the first contraction  244  forms a second limit stop  248  that limits the stroke of the piston  24  in such a way that it cannot leave the bore  26  in flow direction. Thus, the second contraction  242  and the second limit stop  248  form a latching stop  27 . 
     A pressure spring  25  is led on the extension  243  between housing  11  and piston  24 . In operating position this pressure spring  25  is freely movable in longitudinal direction and thus ineffective (FIG.  2 ). 
     The mode of operation of the inventive safety device described in this second practical example is as follows: 
     In this practical example the piston  24 , in combination with the bore  26 , does not only take on the function of the check valve  2  but also that of the cut-off valve  1  as well as that of the pressure sensitive element  3  which results in the simple construction already mentioned elsewhere. 
     If the gas apparatus, placed at the end of the downstream gas pipeline that is not depicted, is out of operation the check valve  2  is closed (FIG.  2 ). The spring-loaded element  117  is in the first contraction  244 , whose limit stop  245  limits the opening stroke when the gas apparatus is in switched on state. If there is now a temperature increase, e.g. due to fire, in the section of the downstream gas pipeline the generated heat causes a pressure rise in this pipeline. This pressure rise effects a stroke of the piston  24  against the flow direction and against the force of the then acting pressure spring  25  that is braced against the housing  11  and the piston  24 . At the same time the stroke moves the extension  243  towards the spring-loaded element  117  so far that the spring-loaded element  117  slides across the conical transition  246  into the second contraction  247 . At a respectively high and undesired pressure rise the stroke of the piston  24  creates a gap between the flexible sealing  242 , formed by the O-ring, and the bore  26  which results in a pressure relief of the downstream pipeline (FIG.  3 ). Following said pressure relief the force of the pressure spring  25  returns the piston  24  into the bore  26 , serving again as seat  16  of the cut-off valve  1 . The latching stop  27  prevents the check valve  2  from opening. The safety device is in the safety position. 
     FIGS. 5 and 6 are schematic representations of a third practical example, as a modification of the second one, of an inventive safety device wherein there is no pressure relief. 
     This inventive safety device also comprises a housing  11  with a gas inlet  113  and a gas outlet  114  depicted as a corner arrangement in this practical example. Gas inlet  113  and gas outlet  114  are each provided with a connection for a gas pipeline not depicted here. 
     Also in this practical example the housing  11  is provided with a check valve  2 , consisting of a piston  24  and a valve seat formed by a bore  26  in the housing  11 , which is preferably tapered in flow direction. Downstream from the bore  26  in flow direction there is a piston  24  which, as in the first and second practical examples, has an O-ring in a circumferential groove  241  as flexible sealing  242  to ensure the gas tightness of the check valve  2  in closed position. The piston  24  is loaded by its own weight against the flow direction. Upstream the bore  26  verges into an expansion  262  whose diameter is smaller than that of the piston  24  with the flexible sealing element  242 . The transition from the expansion  262  to the bore  26  has a limit stop  248  so that the flexible sealing element  242  and the expansion  262  form a latching stop  27  suited for low line pressures. For higher line pressures the latching stop  27  can be executed in such a way that the piston  24  one side has a front-face extension  243  that is led in the guidance section  18  of an aperture  115  as long as the piston is outside of the expansion  262 . The mode of operation of the inventive safety device described in this third practical example, wherein, for the sake of simplicity, there is no pressure relief, as already mentioned elsewhere, is as follows: 
     If the gas apparatus, placed at the end of the downstream from gas pipeline that is not depicted, is out of operation the check valve  2  is closed (FIG.  5 ). The extension  243  is in the guidance section  18 . If now there is a temperature increase, e.g. due to fire, in the section of the downstream gas pipeline the generated heat causes a pressure rise in this pipeline. This pressure rise effects a stroke of the piston  24  against the flow direction and the piston  24  gets into the expansion  262 . The latching stop  27  prevents an opening of the check valve  2 . The safety device is in the safety position. 
     In the version that is suited for higher line pressures the stroke moves the extension  243  in the aperture  115  so far that it leaves the guidance section  18  and, due to a toeing of the extension (Fig.  6 ), gets into the safety position. 
     FIGS. 7 to  12  are schematic representations of a modified practical example of an inventive safety device. In this practical example the safety device is combined with a gas flow control valve  4 . 
     This inventive safety device comprises a housing  11  with a gas inlet  113  and a gas outlet  114  depicted as a corner arrangement in this practical example. Gas inlet  113  and gas outlet  114  are each provided with a connection for a gas pipeline not depicted here. 
     The housing  11  comprises a check valve  2  consisting of a piston  24  and a bore  26  in the housing  11  which form a valve seat that is preferably tapered in flow direction. In flow direction downstream from the bore  26  is a piston  24  which, as in the first practical example, has an O-ring in a circumferential groove  241  as a flexible sealing  242  in order to ensure the gas tightness of the check valve  2  in closed position. The piston  24  is loaded by its own weight against the flow direction. 
     In flow direction downstream from the piston  24  the housing  11  has a second contraction which is formed as the seat  41  of an already known gas flow control valve  4  whose shut-off mechanism is formed by a piston  24  in this practical example. The piston  24  is solidly connected to a longitudinally movable tappet  23  that is led in a slide bearing  221 , arranged in a punched disk  22  that is placed in flow direction downstream from the seat  41  in the housing  11 , and in an aperture  115 . Preferably the tappet  23  has a guide collar  231  that forms a loose fit with the aperture  115 . Next to the aperture  115  is a bore  118  leading outside that is closed in a gastight manner by an inspection plug  17 . The bore  118  is arranged in a staggered way to the aperture  115  so that at least a unilateral locating edge  119  is formed for a thrust piece  33  that is placed in the bore  118  but otherwise longitudinally movable and braced against the inspection plug  17  by a pressure spring  25 , and loaded towards the tappet  23 . The front face of the thrust piece  33  facing the tappet  23  has a funnel-shaped receiver  331  for the tappet. 
     The mode of operation of the inventive safety device with a gas flow control valve  4  described in this fourth practical example is as follows: 
     Also in this practical example the piston  24 , in combination with a seat formed by the bore  26 , does not only take on the function of the check valve  2  but also that of the cut-off valve  1  as well as that of the pressure sensitive element  3  which results in the simple construction already mentioned elsewhere. At the same time the piston  24  is used as a shut-off mechanism for the gas flow control valve  4  whose seat  41  is integrated into the housing  11 . 
     If the gas apparatus, placed at the end of the downstream from gas pipeline that is not depicted, is out of operation the check valve  2  is closed (FIG.  7 ), i.e. the piston  24  is in the area of the bore  26 . In order to prevent upon switching on of the gas apparatus that an abrupt opening stroke moves the piston  24  against the seat  41  the tappet  23  has a guide collar  231 , already mentioned above, which, in combination with the loose fit to the aperture  115  acts as an attenuator. 
     If there is now a temperature increase, e.g. due to fire, in the section of the downstream gas pipeline the generated heat causes a pressure rise in this pipeline. This pressure rise effects a stroke of the piston  24  against the flow direction which initially moves the tappet  23  into the funnel-shaped receiver  331  and then lifts the thrust piece  33 , against the force of the acting pressure spring  25  that is braced against the thrust piece  33  and the inspection plug  17 , from the locating edge  119  and thus releases the locking. 
     At a respectively high and undesired pressure rise the stroke of the piston  24  creates a gap between the flexible sealing  242 , formed by the O-ring, and the bore  26  which results in a pressure relief of the downstream pipeline (FIG.  8 ). Following said pressure relief the force of the pressure spring  25  moves the piston  24  towards the seat  41  which than serves as the seat  16  of the cut-off valve  1  (FIG.  9 ). The safety device is in the safety position. 
     After the removal of the inspection plug  17  the thrust piece  33  can be returned to its initial position and the pressure spring  25  tensioned. 
     If the gas apparatus located at the end of the downstream gas pipeline that is not depicted is in operation, the check valve  2  is in its open position. It is in a working position (FIG.  10 ). The piston  24  is in the area between the bore  26  and the valve seat  41 . If now there is an increase in the gas volume flow in the downstream gas pipeline the piston  24  is moved towards the seat  41 , i.e. the gas flow control valve  4  closes and the safety device is in the safety position (FIG.  11 ). 
     FIG. 12 shows the practical example of an inventive safety device that is schematically represented in FIGS. 7 to  11  and described in detail already elsewhere with an additional manipulator  15  that can be externally actuated and is borne in a gastight manner in a duct in the housing  11  not depicted here. The piston  24  can be lifted from the seat  41  by actuating said manipulator  15 . Thus, the safety device in closed position can be returned to its initial position in non-defective gas pipelines and with closed gas apparatus. 
     As a matter of course the inventive safety device is not restricted to the shown practical examples. There are rather alterations and modifications possible without leaving the scope of the invention. Connections can be varied, for example. Also the described combined sub-assemblies can be executed as individual components or the described parts can be replaced by equivalents. Also a combination of the practical examples described, e.g., in FIGS. 2 to  6  is possible. Moreover, the inventive safety device can also have a manipulator  15  that is externally operable as additionally schematically represented only in FIG. 12 for the fourth example. Also the arrangement of several inventive safety devices in a gas distributor is possible.