A method and apparatus are provided for operating a two position flow valve disposed in a subterranean well, for example a safety valve located near the bottom of a subterranean well, through the application of cyclic pressure applied to fluid confined in the annulus between conduits, such as well casing and a production string. Valving apparatus is provided adjacent to the flow valve to be controlled which derives a pressure signal from the cyclic pressure of the fluid annulus which is effective to maintain the valve in one of its two positions so long as the cyclic pressure exists, but permits the valve to shift to its other position upon termination or significant reduction of the cyclic pressure. In this manner, reliable operation of a flow valve, such as a safety valve, may be achieved without the necessity of running any auxiliary hydraulic control lines to such valve.