Patent ID: 7165425

Claim:
A multi-tube burner comprising: a cylindrical outermost nozzle; and at least one cylindrical inner nozzle provided coaxially with the cylindrical outermost nozzle so as to form annular jet openings for gases used to manufacture a glass preform, wherein the at least one cylindrical inner nozzle comprises a first cylindrical inner nozzle, a second cylindrical inner nozzle which surrounds the first cylindrical inner nozzle, and two or more other cylindrical inner nozzles which surround the second cylindrical inner nozzle, a distal end portion of the first cylindrical inner nozzle is positioned at the same height as a distal end portion of the second cylindrical inner nozzle, at least a glass feed stock gas is discharged from a first jet opening formed at the distal end portion of the first nozzle, and at least an inert gas is discharged from a second jet opening formed between the first nozzle and the second nozzle, a difference in height between the distal end portion of the second cylindrical inner nozzle and a distal end portion of the other cylindrical inner nozzle externally adjacent to the second cylindrical inner nozzle is the same as a difference in height between distal end portions of any two adjacent nozzles selected from the group consisting of the other cylindrical inner nozzles and the cylindrical outermost nozzle, wherein said differences in height are not zero, the heights from the distal end portion of the first cylindrical inner nozzle to the cylindrical outermost nozzle increases, and angles formed between a center axis of an outer circumference of the cylindrical outermost nozzle and distal end portions of all the cylindrical inner nozzles are 90°± not more than 3°.