Flashback prevention in gas burners

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Patented July 28, 1953 2,646,789

UNITED STATES PATENT of FICE

Flash back prevention. n. gas burners

Albert J. Lampert, Walnut, Calif., assignor to

Rheem Manufacturing Company, Richmond,

Calif., a corporation of California

Application October 17, 1950, Serial No. 190,455

. . This invention relates to prevention of flash A typical gas burner consists of a burner mem back and consequent extinction noise when a gas ber, or head, having outlet ports at which the burner is turned off. air-gas mixture burns to heat Some type of

It is an object of this invention to prevent 5 heater, or heat exchanger. Suitable conduit flashback from burner ports into the conduit means communicates with the head to conduct feeding the burner with combustion gas. air-gas mixture thereto. It is customary to feed It is another object of this invention to prevent combustion gas to the conduit means through a extinction explosion resulting from flashback nozzle, or other orifice, adjacent which are a when the gas supply to a burner is cut off. number of apertures by means of which combus Flashback, prevention means have taken the 10 tion air, in this case primary air, is aspirated by form of screens or grids interposed across the the well-known Bernoulli principle into the con conduit leading to the burner. These Screens are duit means. Thus, a mixture of air and gas is generally within or adjacent the burner head or fed through the conduit means into the burner member. There are two theories as to how such head and out the burner ports where combustion screens operate. One theory is that the Screens 15 takes place.

have. Sufficient heat capacity to absorb the flanne When the shut-off valve in the gas line is as it travels, or flashes, back in the conduit, closed, flow of gas from the nozzle ceases. The thereby lowering the temperature below the igni momentum of the air-gas mixture already flow tion point and preventing: continued passage of ing in the conduit continues to carry it toward the flame. Another theory, somewhat more the burner head and continues to draw primary widely held, is that such screens, by their in air in through the apertures. Thus, for a short herent restricting properties, accelerate the for time immediately following closing of the gas ward flow of gas and air to a velocity greater than valve, a progressively rarer air-gas mixture is fed the propagation velocity of the flashing-back to the burner head; that is, the ratio of gas to flame. Thus, as the flame reaches the screen it airThe progressively decreases.

velocity of flame propagation increases as encounters a region where the gas flow in a for the gas-to-air ratio decreases. Since the residual ward direction is greater than the flame velocity air-gas mixture is steadily slowing down, the two backward, and the flame is consequently extin effects combine until a point is reached where guished. - - the flame propagation velocity exceeds the flow

Regardless of the theory adopted, it is an in- . Velocity herent property of such screens that they serve of the mixture. At this point the flame to restrict the flow of gas with the consequent at. the burner penetrates the outlet ports and disadvantage of loss of pressure at the burner propagates backwardly in the gas conduit until it reaches the nozzle, at which time all the air

It is another object of this invention to prevent 35 gas mixture has been burned. This phenomenon flashback in gas burners without introducing re is known as flashback and is generally attended by a loud popping or extinction noise.

strictions of any type in the normal flow of gas to the burner head. w In accordance With the instant invention flash It has also been proposed to lead the incoming back is prevented-not by blocking the flashback gas through a tortuous path, thereby providing 40 flame, as with a screen-but by removing the an elevated trap in which the gas tends to gather, residual air-gas mixture rapidly from the burner thus blocking any residual flow of air-gas mix member and the conduit, thereby leaving nothing ture, which is the initiating cause of the flash to be burned. This is effected by placing a con back in the first place. This tortuous path like duit, or flashback prevention tube, in communi Wise introduces impedance to the flow of gas to 45 cation with the gas conduit, preferably adjacent the burner head. With resulting loss in pressure the gas nozzle and air apertures. The flashback at the head. . . prevention tube is positioned with at least a por It is a further object of this invention to pre tion thereof extending upwardly in heat receiv vent flashback without introducing any type of ing disposition with respect to the heater which impedance to the gas flow, thereby maintaining 50 is heated by the flame at the burner head. The full pressure at the burner head. .. . . Ahback prevention tube is open at its upper ... In accordance with the above objects and with others which will become apparent throughout When the apparatus is in operation, the flash the ensuing specification, the instant invention back prevention tube is heated by the heater so will now be described. . . . 55 that the air therein tends to rise. There is a 3 contrary tendency of the air in the flashback pie created wherein the upward convection force in vention tube to be drawn downwardly into the the tube 22 balances the downward aspirating gas conduit because of the aspirating action of force from the nozzle 6, so that air in the tube the gas nozzle. The net effect is, With picper 22 is Substantially dormant. As a matter of design, a balance in which the air in the flash 5 Safety, to insure against gas flow out of the upper back prevention tube is substantially dormant. end of the tube 22, it is preferred to design the When the gas flow is shut off by closing the structure so that the net tendency is a slight gas valve, the aspirating influence within the downflow in the tube 22, thereby precluding any flashback prevention tube immediately ceases. escape of combustion gas. The convection tendency of the heated air now () When the valve 8 is suddenly closed, as is the pulls the air therein upwardly and out the open case with automatic solenoid-operated valves, the end. This creates a suction effect which, over aspirating effect at the nozzle 6 abruptly ceases. coming the residual momentum of the air-gas Residual momentum of the air-gas mixture in mixture in the gas conduit, rapidly draws the the conduit i3 continues, however, to draw in mixture out of the conduit and up the flashback atmospheric air through the apertures 2 ?, there prevention tube. The burner head and conduit by thinning out the mixture in the conduit 3 and are thus emptied of combustible mixture so that raising its flame propagation Velocity. no fashback occurS. However, as Soon as gas flow ceases from the In accordance with the above description a nozzle 6, the convection tendency in the tube 22 specific embodiment of the instant invention will immediately starts to draw the air-gas mixture now be described in conjunction with the accom out of the housing 4 and conduit 3. The panying drawings wherein: residual momentum of the air-gas mixture in Figure 1 is an elevational view of apparatus conduit 3 is thus almost immediately arrested, embodying the instant invention; and the flow is reversed back toward the housing Figure 2 is a detail view showing the burner 2 5 4 and up the pipe 22, Thus, before the mixture and bottom portion of the flashback prevention in the burner member can be thinned out to tube; and the flashback point, the entire combustible mix Figure 3 is a sectional view taken on line 3-3 ture in the housing 3 is emptied through the of Figure 2. tube 22 and flashback is effectively prevented. Referring to the drawings, designates a 3 ) While the instant invention has been shown and burner member, or head, having the usual out described herein in what is conceived to be the let ports at the top thereof at which flames 2 most practical and preferred embodiment, it is burn. Conduit means in the form of a burner recognized that departures may be made there conduit i3 communicates with the burner head from within the Scope of the invention, which is and terminates at an aspirator housing 4. Pro 3 5 therefore not to be limited to the details dis jecting into the housing 4 is a gas nozzle 6 closed herein but is to be accorded the ful Scope connected to a gas line by means of which of the claims So as to embrace any and all equiva combustible gas under pressure is fed to the noz lent methods and apparatus.

zle 6. A valve 3 is interposed in the line What is claimed is:

to control the flow therethrough. Heater means i. 1. In a gas burner including a burner member in the form of a heat exchange housing 9 is dis having outlet port means, conduit means con posed above the burner member to be heated municating with said burner member adapted to by the gas flames 2. feed gas thereto, an apertured aspirator housing Referring more particularly to Figures 2 and 3, formed on the end of said conduit means, a nOZ the housing 4, into which the nozzle 6 pro zle extending into said housing and adapted to be jects, is provided with a plurality of apertures connected to a source of combustion gas, whereby 2 by means of which air is aspirated from the to draw in combustion air through the housing atmosphere into the conduit i3 by the injector apertures as it flows to said burner member, and effect of the nozzle 6. heater means positioned to be heated by gas In accordance with the instant invention a burned at said burner member, the combination second conduit in the form of a flashback preven of a flashback prevention tube communicating at tion tube 22 communicates with the housing A one end with said housing adjacent the mouth at the top thereof and extends upwardly adjacent of said nozzle and extending upwardly in heat the heater 9, so that the air in the tube 22 is receiving disposition with respect to said heater heated from the heater 9. The tube 22 is open means, the upper end of said tube being open to at its upper end. atmosphere.

Operation 2. In a gas burner including a burner member having outlet port means, first conduit means

Operation of the instant invention is as fol communicating with said burner member adapted lows: 60 to feed gas thereto, orifice means positioned to When gas valve 8 is turned On, gas flows direct combustible gas into said first conduit through the nozzle f6 into the conduit 13, bustion means, said first conduit means having a con aspirating primary air into the housing 4 and air inlet opening adjacent said orifice conduit 3 through the apertures 2. This corn means, and heater means positioned to be heated bustible air-gas mixture flows from the burner by gas burned at said burner member, the con member through the ports thereof and pro bination of second conduit means communicat duces, when ignited, the heating flames 2. The ing at one end With Said first conduit means ad hot gases from the flames 2 pass upwardly and jacent said orifice means and being open at the heat the heater 9. other end, and extending upwardly in heat re As the heater 9 warms up it also Warms the ceiving disposition. With respect to said heater air in the nearby flashback prevention tube 22. rea.S. s

In the initial stages of operation, air flows down 3. In a gas burner including a burner member wardly through the tube 22 into the conduit 3 having outlet port means, first conduit means because of the aspirating effect of the nozzle 6. communicating with said burner member adapted As the tube 22 heats up, however, a balance is to feed gas thereto, orifice means positioned to 4 direct combustible gas into said first conduit communicating with said burner member adapted means, said first conduit means having a COm to feed gas thereto, orifice means communicat bustion air inlet opening adjacent said Orifice ing with said first conduit means and adapted to means, and heater means positioned to be heated be connected to a source of combustion gas, and by gas burned at Said burner member, the com heater means positioned to be heated by gas bination of Second conduit means communicat burned at said burner member, the combination ing With said first conduit means adjacent said of second conduit means communicating at one orifice means and being open at one end, at least end with said first conduit means adjacent said a portion of said second conduit means extend orifice means, at least a portion of said second ing upwardly in heat receiving disposition with 0. conduit means extending upwardly in heat re respect to said heater means. ceiving disposition. With respect to said heater 4. In a gas burner including a burner member means, said Second conduit means terminating in having outlet port means, first conduit means an open end disposed exteriorly of said heater communicating with said burner member adapted means and out of communication thereWith. to feed gas thereto, orifice means communicating 5 ALBERT. J. LAMPERT. With Said first conduit means and adapted to be connected to a source of combustion gas, and References Cited in the file of this patent heater means positioned to be heated by gas UNITED STATES PATENTS burned at Said burner member, the combination Number Name Date of second conduit means communicating at one 416,130 Walters ----------- Nov. 26, 1889 end with said first conduit means adjacent said 763,057 Hutchinson -------- June 21, 1904 orifice means, extending upwardly in heat receiv 1,074,157 Beler ------------- Sept. 30, 1913 ing disposition. With respect to said heater means, 1,079,327 Chadborn ---------- Nov. 25, 1913 and terminating in an open end disposed exte 1,105,987 McSorley ----------- Aug. 4, 1914 riorly of said heater means and out of communi 1562,590 Rodgers ----------- Nov. 24, 1925 cation thereWith. 2,062,605 Peters -------------- Dec. 1, 1936 5. In a gas burner including a burner member 2,200,264 Dennis et al. ------- May 14, 1940 having outlet port means, first conduit means