Abstract: An assembly adapted to be anchored at a subsurface location within a tubular well conduit to function as a self-closing safety valve. The assembly includes a flapper valve closure element pivotably mounted in a tubular valve housing and controlled by a pressure sensitive control mechanism. An anchoring means having radially expansible anchoring and sealing members is employed to secure the valve in place and to form a seal which forces fluid in the conduit to flow through a flow passage in the valve housing. The expansible anchoring and sealing means may be retracted to permit retrieval of the entire assembly. The control mechanism includes a pressure charged bellows chamber which moves in response to a drop in the pressure within the well conduit to cause the flapper to close the flow passage.An incompressible fluid contained within the bellows of the control mechanism cooperates with a double acting valve to prevent over extension or over compression of the bellows by extremes in pressure differential.