(57) A duct for the escape of flue gas and for the intake of combustion gas, particularly
for boilers, or the like, which duct comprises two concentric tubular elements (1,2),
means (103,504) being provided for connection therebetween at least at the outer end
of the duct. The invention provides that the outer pipe (2) has means (103) for locking
the inner pipe (1) at least axially, which means can be operated or disabled from
the inner pipe.
The invention also provides a duct as described hereinbefore, whose length is telescopically
adjustable.
Said characteristics may be also applied, individually or in combination, to one-pipe
ducts.
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