Abstract: A filling system for a toilet tank prevents continual flow to the tank in the event of a leak from the tank by providing a hydraulically actuated safety valve for halting water flow to the filling valve in the event that the water flow continues for a time longer than an expected time of filling. The safety valve has a valve member connected to a piston mounted in a cylinder defining a first chamber on one side of the piston and a second chamber on the other side. A venturi in the supply duct provides in a low pressure chamber of the venturi a water pressure lower than the supply pipe pressure such that a pressure difference across the piston caused by the difference in pressure between the supply pressure and the low pressure chamber causes the piston to move from the first end toward the second end. A flow control orifice regulates a rate of flow of water such that a time of movement of the piston is greater than an expected time required to fill the toilet tank.