Gases to be silenced are caused to partake of a whirling motion close to the inner surface and past the reticulations of the reticulated wall of a chamber arranged within an outer casing. Substantially the whole of the gases flow past the reticulations from a relatively restricted inlet to an outlet, and the whirling motion may be imparted by a deflector plate or curved vane or by a tangential inlet. A casing 1 has at one end a portion 50 terminating in a hemispherical cap 51 with inlet 54, and at the other end a plate 3 with eccentric outlet 5 and a pipe 9 attached thereto. The interior of portion 50 is separated from the interior of the rest of the casing by a plate 2 having an eccentric aperture 4 behind which is a deflector plate 10. Within the portion 50 are hollow conical frusta 52, 53 abutting at their larger ends. The small end of frustum 52 is connected to the inlet 54, while the small end of frustum 53 is connected to the aperture 4. Within the casing 1 are a pair of frustoconical chambers 6, 7 with reticulated walls, the smaller end of chamber (5 entering the larger end of chamber 7 eccentrically, and the smaller end of chamber 7 terminating in the outlet pipe 9. The deflector plate 10, adapted to whirl the gases, is located close to the wall of chamber 6 and comprises a portion 11 inclined to the longitudinal axis of the casing with an edge in contact with the internal surface of chamber 6, and a portion 12 arranged parallel to the axis of the chamber. A similar plate is located behind the entrance to chamber 7. The spaces between the frusta 52, 53 and the outer casing are filled with sound‐absorbing material 57 such as asbestos or coke, or, alternatively, sheet asbestos may be wound round the frusta. The space between the chambers 6, 7 and the casing serves as a cushioning space and may also be filled with sound‐absorbing material such as steel wool, or fibrous asbestos or with material adapted to absorb poisonous gases. An opening 13 may be provided for the removal of solid matter. In a modification (Fig. 2) the inlet pipe 59 is secured to an end plate 58 forming the base of the conical chamber 60, the smaller end of which passes through an eccentric opening in diaphragm 2 into a cylindrical reticulated chamber 15 supported by a diaphragm 16, and is extended by a pipe 62 adapted to direct the gases on to a portion 20 of a deflector plate on the side remote from an aperture 21. The gases then pass through aperture 21 and flow along the inner surface of the chamber with a gyratory motion. A second deflector plate 22, similar to the first, is situated in the chamber 15. In both constructions, the second deflector plate may produce whirling in the same or an opposite direction to the first. In a modification, the reticulated chambers are of spherical form. In Fig. 4 gases enter the chambers 38 tangentially by a pipe 39 and leave by pipes 40, 41. In Figs. 5 to 8 (not shown) different arrangements and combinations of chambers within the casing are described, and in two of the forms, suitable for aircraft, the casing is conical and provided at its rearward or smaller end with a number of perforations to give a gradual outlet. Specification 366,257 is referred to in the Provisional Specification.
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