US 3558253 A
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.1511.251971 C SMWH Em 3,558,253
" I BLow PIPEs Filed NOV. 26' 1968 INVENTORS WILFRED C. SMITH RICHARD W. J. COX
BY Mouw United States Patent O 3,558,253 BLOW PIPES Wilfred C. Smith, Hackmans Gate, near Clent, and Richard W. J. Cox, Kidderminster, England, assignors to William Allday and Company Limited, Stourporton-Severn, Worcestershire, England, a British company Filed Nov. 26, 1968, Ser. No. 779,144 Claims priority, application Great Britain, Dec. 2, 1967, 54,941/ 67 Int. Cl. F23d 15/02 U.S. Cl. 431--353 7 Claims ABSTRACT OF THE DISCLOSURE A blowpipe head for burning gas fuel, for example natural gas, in combination with pressurized air having a chamber for connection to gas fuel and air supplies and a burner tube in which mixed gas fuel and air is burnt; wherein a restricted venturi throat passage leading from the chamber to the burner tube is axially aligned with an air nozzle in the chamber to direct a jet of the pressurized air through the throat, so that gas fuel fed into the chamber is drawn through the throat and mixed with the air.
This invention releates to blowpipe heads fuelled by inflammable gas particularly, but not exclusively, natural gas.
The object of the invention is to provide a blowpipe head which produces a stable flame with a wide range of control, while avoiding setting up back pressure in the gas fuel supply line.
According to the invention a blowpipe head including a chamber for connection to a supply of gas fuel and air pressure, and a burner tube in which a mixture of the -gas fuel and air is burnt in use is characterised in that a restricted venturi throat passage between the chamber and the burner tube is axially aligned with an air nozzle aligned in the chamber to direct a jet of the pressurized air through the throat.
A preferred embodiment of the invention is now more particularly described with reference to the accompanying drawing showing a longitudinal cross section of a blowpipe head according to the invention.
The blowpipe comprises a body section 11 having an axial bore including at one end a screw threaded socket for engagement with a burner tube 12. The bore is radially enlarged over part of its length to form a chamber 13 adjacent to the socket. The unenlarged part of the bore of the body has a threaded portion 14 for mounting an air nozzle 15 having its jet orifice aligned coaxial within the bore.
The air nozzle exterior and the internal wall of the chamber 13 define an annular cavity therebetween to which Igas fuel is admitted by a duct 16 passing obliquely through the body wall for connection to a gas fuel supply.
Coaxially aligned with the jet orifice of its air nozzle 15 is a venturi tube 17 forming a reduced diameter throat opening between the chamber 13 and the burner 12. Part 21 of the bore of the venturi tube 17 is parallel with a diameter greater than that of the air jet orifice and less than that of the chamber 13, this part 21 adjoining the burner tube 12. The remainder of the bore diverges from part 21 to form a tapered mouth 18 with its greatest diameter inner end projecting into the chamber 13 around but spaced from the tip 22 of the air nozzle 15.
The tip 22 of the air nozzle 15 is of frustoconical shape at 19, complementary to the tapered mouth 18 of the venturi tube, so as to define a parallel sided axially converging annular outlet 20 at one end of the chamber, leading into the restricted throat formed by the bore 21 Patented Jan. 26, 1971 lCe of venturi tube 17 and thence into the larger diameter burner tube 12.
A part 23 of the smaller diameter bore in the end of the body section 11 most remote from chamber 13 has a duct 24 in its wall parallel to the duct 16 in the wall of the chamber, said duct 24 serving to admit a supply of pressurized air to the nozzle 15, which supply is regulated by means of a needle principle valve 25 adjustably mounted in the extreme outer end of the body bore 23 by an exteriorly projecting screw stem 26.
The burner tube 12 has an internal baffle 28 axially spaced from the venturi tube 17, said baffle having a central bore 30 coaxial with the burner tube, and three outer helical passages 31 defined by the inner wall of the burner tube and the flanks of a three start very coarse V section thread turned in the outer cylindrical surface of the baffle 28 before insertion in the burner tube 12.
The burner tube 12 and venturi tube 17 are integral or united and are removable as a unit by unscrewing from the threaded socket of body 11. Thus different sizes or types of burner tube and venturi are interchangeable with a common body portion 11 for use in different applications.
A hook 32 is provided on the outer surface of duct 16 for suspending the blowpipe when not in use.
In operation the jet of pressurized air issuing from the nozzle 15 through the venturi tube 17 induces suction in the chamber 13 and gas duct 16 to draw the gas fuel with the air through the venturi tube into the burner tube 12. The gas fuel and air flow are further mixed together as they pass through the bafe 28, part of the fiow being given a swirling motion through the spiral passages 31.
The swirling of part of the burning gases ensures stable and effective combustion in a flame produced and retained at the outer end of the burner tube 12, having especial application in the case of natural gas or other fuel gases which have slow combustion characteristics.
Variation in air pressure is compensated by adjustment of valve 25. Control of the ow of gas fuel through duct 16 and air through duct 24 is effected by controls (not shown) on each of these ducts.
1. A blowpipe head including a chamber for connection to a supply of gas fuel air pressure, a burner tube in which a mixture of the fuel and air is burned in use, means defining a restricted venturi throat interconnecting the chamber and the tube, means for supplying gas fuel to said chamber, an air nozzle located in said chamber in axial alignment with said throat to direct a jet of pressurized air therethrough, and a baffle located in said burner tube at a position remote and downstream from the throat, which baffle has an inner through passage coaxial with said tube and said throat and at least one outer substantially helical duct for inducing a swirling motion to a part of the gases passing through the baffle.
2. A blowpipe according to claim 1 wherein said baffle has a plurality of outer helical ducts.
`3. A blowpipe head according to claim 2 for use with natural gas fuel wherein the internal cross-sectional area of the inner through passage of the baille is substantially one-ninth of the like area of the burner tube bore, the internal cross-sectional area of the air nozzle bore is substantially one-third said burner tube bore area, and the total effective cross-sectional area of said outer helical ducts of the baie measured on a plane normal to the direction of flow therethrough is substantially one-third said area of the inner through passage.
4. A blowpipe head according to claim 1 characterized in that a frusto-concial entrance (18) to the throat (21) within the chamber (13) and a frustowhich are mounted the air nozzle (15), throat (17) and 5 burner tube (12), said body portion having connections (16), (24) to receive a supply of gas fuel and of pressurized air in use.
6. A blowpipe head according to claim 5 characterized in that the body portion (11) includes an adjustable valve (25) for regulating the flow of pressurized air through the air nozzle (15).
7. A blowpipe head according to claim 1 characterized 1o in that the burner tube (12) and throat (17) are dismountable from the chamber (13) and interchangeable with burner tubes and throats of other types and sizes.
References Cited UNITED STATES PATENTS 371,157 10i/1887 Wright 239-416 1,231,726 7/1917 Gault 431-353 1,569,163 1/1926 Waldron Z39-401K 1,748,004 2/ 1930 Urquhart Z39-416K 2,239,025 4/ 1941 Vigneault 431-354 2,720,257 10/ 1955 Lynes 431-353 CARROLL B. DORITY, JR., Primary Examiner U.S. Cl. X.R. 239-399