초록 ▼

A flue ducting for atmospheric boilers is disclosed and comprises two coaxial generally tubular ducts 10, 11, and a generally undulating linear spacer 12 between said ducts. Linear features are provided on the mutually facing surfaces of the ducts, the features being shaped to engage the undulating

A flue ducting for atmospheric boilers is disclosed and comprises two coaxial generally tubular ducts 10, 11, and a generally undulating linear spacer 12 between said ducts. Linear features are provided on the mutually facing surfaces of the ducts, the features being shaped to engage the undulating spacer 12. One end of the annular space between the ducts 10, 11 is closed.

대표청구항 ▼

[ What is claimed is:] [1.]1. A flue ducting comprising concentric inner and outer pipes defining an annular air space therebetween extending a length of the ducting, corresponding helical grooves being formed in opposed surfaces of the inner and outer pipes to extend the length of the pipes, and a

[ What is claimed is:] [1.]1. A flue ducting comprising concentric inner and outer pipes defining an annular air space therebetween extending a length of the ducting, corresponding helical grooves being formed in opposed surfaces of the inner and outer pipes to extend the length of the pipes, and a helically coiled spring being located in said grooves to react between the inner and outer pipes, said helically coiled spring having individual coils which are of undulating shape defining alternating peaks and troughs therearound with the peaks therein engaging in the helical groove in the outer pipe and the troughs therein engaging in the helical groove in the inner pipe to determine and maintain the space between the inner and outer pipes, a flexibility of the ducting so formed enabling the length and a longitudinal configuration thereof to be varied, one end of the annular space between the pipes being closed.