Patent ID: 7520298

Claim:
A system for providing alternating pressure and vacuum pulses to a conduit comprising: a source of pressure and vacuum; and a rotary valve communicating with the source of pressure and vacuum, wherein the rotary valve comprises: an outer sleeve having pressure and vacuum ports in flow communication with the source of pressure and vacuum, and an outlet port for delivering the alternating pressure and vacuum pulses to the conduit; and a generally cylindrical inner sleeve rotatably mounted at least partially inside the outer sleeve and including pressure and vacuum ports, wherein when the inner sleeve is located at a first rotational position with respect to the outer sleeve a pressure port of the inner sleeve is aligned with the pressure port of the outer sleeve to deliver pressure to the outlet port of the outer sleeve, and when the inner sleeve is located at a second rotational position with respect to the outer sleeve the vacuum port of the inner sleeve is aligned with the vacuum port of the outer sleeve to deliver vacuum to the outlet port of the outer sleeve, and wherein the pressure and vacuum ports of the inner sleeve are located at different positions along an axial length of the inner sleeve.