An apparatus employing pressure transients for transporting fluids from one reservoir to another, includes an at least partly enclosed space, and a body herein, where the body is movable relatively to the interior of the space. The apparatus further includes an opening in the enclosed space to allow a fluid to flow alternately in the direction into and out, and conduits in fluid communication with the opening and connected to the reservoirs. Further, an object is arranged to collide with the body so as to generate pressure transients in the partly enclosed space in order to produce a flow of fluid in the direction from the partly enclosed space towards the second reservoir, and to produce a flow of fluid in the direction from the first reservoir towards the partly enclosed space.