A cyclonic separating apparatus for separating solid material from a fluid
includes a separating chamber, an inlet communicating with the separating
chamber for carrying the fluid with the solid matter entrained therein to
the separating chamber, and an outlet for carrying the fluid away from
the separating chamber after the solid material has been separated
therefrom. The outlet is formed by a conduit communicating with the
interior of the separating chamber and having a longitudinal axis. A
plurality of grooves are formed in an interior surface of the conduit
outlet and extend in the same direction as the longitudinal axis. The
presence of the grooves in the outlet has the effect of reducing noise
generated by the apparatus when in use and also improves pressure
recovery.