the figures generally illustrate preferred embodiments of the venturi tube , also referred to as a mixing tube , of the present invention . the venturi tube serves to introduce primary combustion air into the flow of combustible gas enroute from a fuel supply to a point of combustion such as the burner of a barbecue device . the tube configuration , and more particularly , the baffling arranged about the intake orifice serves to render the device substantially less susceptible to gusting wind . fig1 is perspective view of a venturi tube 102 of the present invention adapted for use with a barbecue device 12 . combustible gas is conducted from a source 40 to a burner 38 via a conduit 30 . the mixing venturi tube of the present invention is positioned in line with the conduit at a point upstream of the burner and in a well ventilated location in order to ensure that fresh air has unhindered access thereto . the need to position the venturi tube in a relatively open location is what often contributes to the susceptibility of such devices to gusting winds . a gust passing over the venturi tube can cause a sudden over - pressure or under - pressure which disrupts the amount of combustion air that enters the fuel stream which in turn may cause the flame to extinguish . fig2 is an enlarged view of the circled region 2 of fig1 showing the interior structure of the venturi tube 102 in longitudinal cross - section . the passage way 104 extending therethrough has a section 106 of restricted cross - section so as to cause the flow 108 of gaseous fuel there through to accelerate and create a zone of low pressure . one or more intake orifices 110 are formed in the wall of the passage way in a position so as to take advantage of the low pressure zone . an inner baffle 112 is disposed about the exterior of the passage way wherein the proximal end 114 of the inner baffle is closed off and positioned proximal to the intake orifices while its distal end 116 is open and positioned distal to the intake orifices . an outer baffle 118 of greater diameter is disposed about the exterior of the inner baffle . its proximal end 120 is open and is positioned proximal to the distal end of the inner baffle while its distal end 122 is closed and is positioned distal to the open distal end of the inner baffle . a flowpath 124 is thereby defined that requires incoming primary combustion air to undergo at least two 180 ° changes in direction , one to reach the intake orifice and another to enter the stream of gaseous fuel 108 . additionally , a substantially volume 126 is enclosed within the baffling . fig3 is a transverse cross - section taken along line 3 - 3 of fig2 illustrating the non - concentric arrangement of the inner and outer baffles 112 , 118 in this particular embodiment . the baffles are attached to one another at 128 so as to define an opening 130 of varying width extending about the circumference of the inner baffle . fig4 is an enlarged view of a preferred alternative embodiment showing the interior structure of the venturi tube 132 in longitudinal cross - section . the passage way 104 extending therethrough has a section 106 of restricted cross - section so as to cause the flow 108 of gaseous fuel there through to accelerate and create a zone of low pressure . one or more intake orifices 110 are formed in the wall of the passage way in a position so as to take advantage of the low pressure zone . an inner baffle 142 is disposed about the exterior of the passage way wherein the proximal end 144 of the baffle is closed off and positioned proximal to the intake orifices while its distal end 146 is open and positioned distal to the intake orifices . an outer baffle 148 of greater diameter is disposed about the exterior of the inner baffle . its proximal end 150 is open and is positioned proximal to the distal end of the inner baffle while its distal end 152 is closed off and is positioned distal to the open distal end of the inner baffle . a flowpath 154 is thereby defined that requires incoming primary combustion air to undergo at least two 180 ° changes in direction , one to reach the intake orifices and another to enter the stream of gaseous fuel 108 . additionally , a substantial volume 156 is enclosed within the baffling . fig5 is a transverse cross - section taken along line 5 - 5 of fig4 illustrating the concentric arrangement of the inner and outer baffles 142 , 148 in this particular embodiment . the baffles cooperate to define an opening 160 of constant width extending about the circumference of the inner baffle . in use , the venturi tube 102 of the present invention is inserted between a fuel supply and a burner . gaseous fuel flowing 108 through the interior passageway 104 encounters a restriction 106 that induces a low pressure zone which in turn causes air to be drawn into the flow via intake orifices 110 . the primary combustion air is drawn in from the exterior of the device into the fuel flow via a circuitous path 124 , 154 as defined by the overlapping configuration of the baffles 112 , 118 and 142 , 148 . the air flow makes a first 180 ° turn to enter the inner baffle 112 , 142 and a second 180 ° turn to enter the gas stream . it is believed that the changes in direction and the relatively long flow path serves to stabilize the velocity with which the primary combustion air enters the fuel stream to thereby minimize the effect of wind blowing over the exterior of the device . similarly , the volume 126 , 156 of air within the device is believed to have a stabilizing influence on any pressure fluctuations the exterior of the device may be subjected to . it has also unexpectedly been found that the non - constant width of the opening 130 of the embodiment shown in fig1 - 3 seems to have a further stabilizing influence on the performance of the device , possibly preventing the formation of any standing waves or harmonics that may be created by air flowing over the device that could possibly have an adverse effect on the amount of primary combustion air entering the fuel stream . while particular forms of the invention have been described and illustrated , it will also be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention . for example the size and shape of the baffles may be changed to accommodate particular applications . additionally , more baffles may be added in order to require the incoming air to follow an even more circuitous route to the intake orifices . accordingly , it is not intended that the invention be limited except by the appended claims .
a venturi tube has a configuration of baffles affixed thereto that serve to greatly reduce the susceptibility of a gas burning appliance to wind gusts . the baffles cooperate to force incoming primary combustion air through a circuitous route before introduction into a flow of gaseous fuel . the circuitous route in combination with the volume of air that is contained within the baffling serves to substantially reduce flame blowout .