Abstract: The safety valve assembly of the present invention for use in a closed fluid system comprises a valve housing including a central throughbore divided into an inlet end and an outlet end which communicate with one another via an axial passageway parallel thereto. Access to an inlet of the passageway is controlled by a valve element which is movable between a standby position solely in response to a differential fluidic pressure developed when a leak develops in the closed fluid system downstream of the safety valve assembly to isolate the leak from the remainder of the system. A bleeder valve assembly is also provided to return the assembly to a standby position thereof once the downstream leak has been eliminated.