According to the invention, discharge noise from rotary vacuum machines
having complementary profiles is attenuated by interposing between the
discharge from the primary pump and the outlet to the atmosphere, a
transfer device having independent cavities, e.g. cavities on a rotor
rotated on a shaft, the cavities moving sequentially from the discharge to
the outlet while simultaneously providing isolation between the discharge
and the outlet. This achieves dynamic attenuation of the noise in a manner
that is particularly simple and low cost, while also being very effective
in suppressing discharge noise.
