Abstract: A silencer consists of concentric spaced apart longitudinally extending shells connecting two bulkheads, each having an outer imperforate face, the space between the faces of each shell containing noise absorbing material such as rock wool. Each shell has a longitudinally extending duct to enable the gases to escape, the duct in the inner shell being offset in relation to the duct in the next shell; the inner shell is connected to the inlet pipe and the gases escape via the duct of the inner shell, then through the space separating the two shells and finally through the duct of the next shell.