Abstract: A apparatus for feeding concrete and other thick materials from a container into a feeding pipe by two feeding cylinders which are alternately connectable by a switching device to the container or the feeding pipe. The feeding pistons of the feeding cylinders alternately perform a suction stroke and a pressure stroke, with the average piston speed being at least temporarily greater during the suction stroke than during the pressure stroke. A continuous feeding flow is achieved in that during the switching period t.sub.u of the switching device the two feeding cylinders are substantially separated from the container at least temporarily and are short-circuited together to form a joint conenction with the feeding pipe. In this state, the one feeding piston is still finishing its pressure stroke while the other feeding piston already begins its pressure stroke at the same time.

Abstract: The invention relates to a concrete mixer truck having a rotatably driven mixer drum, particularly a drum provided with interior mixing elements, and a hydraulic system as a drive source for the mixing process.It is intended to enhance the effect of the mixing process by transmitting vibration energy to the mixture materials. To this effect, a vibration generator is included in the hydraulic system in such a manner that pressure pulses generated in the flow of the hydraulic fluid are superimposed on the mixing movement in the form of vibrations. This superposition effect may be achieved with respect to the rotation of the drum and/or with respect to the movements of a separate mixing tool.