| 摘要 |
A burner head including a blast tube (3) and a device for controlling the air flow through the blast tube (3), the flow controlling device comprising a flow constrictor (11) which is alterable between a first configuration and a second configuration in which the flow constrictor (11) extends radially across an annular portion of the blast tube (3) to reduce the cross-sectional area in the blast tube (3) available for unobstructed air flow. |
