Apparatus for impelling liquid

Apparatus for cylically impelling liquid by means of gas under pressure, comprising a duct for the liquid, a flexible partition having a zone anchored with respect to said duct and extending from said anchored zone downstream along the duct, an opening in the wall of the liquid duct and a gas duct communicating with such opening for the supply of gas under pressure to said opening, the opening being adjacent, and on the downstream side of, the anchored zone of the partition, a valve member carried by, or formed by part of, the partition, and resilient means urging the valve member to close the opening until the pressure of gas accumulating in the gas duct is sufficient to overcome the resilient means and deliver through the opening a pulse of gas for causing the partition to impel liquid, the partition being capable of deformation between a first position in which it substantially conforms to the liquid duct wall and covers said opening while leaving the liquid duct substantially unobstructed, and a second position in which the opening is uncovered so that gas, having attained sufficient pressure to overcome said resilient means, is directed downstream by the partition while the partition inflates across the liquid duct, said liquid duct being of substantially constant cross-section along its length, such cross section being substantially circular, said partition being tubular and extending substantially the whole length of said duct, said anchored zone of said partition being oblique with respect to the longitudinal axis of said liquid duct, said partition being oriented with its portion adjacent said opening being the furthest upstream portion of said partition, an openwork support structure mounted with its periphery adjacent the anchor zone of the partition and acting as a support for the partition against deformation beyond a predetermined configuration under gas pressure, the partition having free end portions forming non-return flap valves, said gas duct extending through the wall of said liquid duct, said opening being defined by the end of said gas duct disposed within said liquid duct, said gas duct and said opening lying on an axis extending substantially perpendicular to the portion of said flexible partition anchored with respect to said liquid duct in opposed, adjacent relation to the end of said gas duct defining said opening, said resilient means defining a spring disposed internally of said gas duct, said spring being a tension spring fixed to the opposed portion of said flexible partition.