Abstract: Safety valve for a hydraulic circuit supplying a hydraulic receiver having an inlet and an outlet connected to the receiver which includes between the inlet and the outlet a non-return module which has a non-return valve and a selectively operable valve having an unoperated position in which the non-return valve prevents any reverse flow of fluid from the outlet to the inlet and an operated position in which such reverse flow is made possible. A control inlet is provided for applying control pressure to the selectively operable valve. A pressure relief valve is provided between the outlet and the control inlet which is adapted to enable flow from the outlet to the control inlet from a predetermined pressure threshold.