Abstract: The invention relates to a split hopper vessel consisting of two halves, which can swing about a horizontal longitudinal axis between a closed position in which the hold formed by the two halves is closed and an open position in which the two halves are moved apart. The two halves are interconnected by hydraulic cylinders which can perform or assist the opening and/or closing of the vessel. The hydraulic cylinders under the control of non-return valves (10,11,53) which block the closed position and which by a control pressure system can open to allow the opening of the vessel. The flow of liquid from one side of each cylinder to the other side can be shortened, and safety structure ensures that all cylinders operate simultaneously, all non-return valves (10,11) having a pressure-activated switch, which when activated opens the non-return valve G.sub.1 in the line connecting both sides of each cylinder.