A containment valve assembly using the upcoming pressures to control the flow of oil/gas through a riser pipe with a stop flow plug positioned within the valve housing that has an outer surface shaped to fit within and against the riser pipe, and an inner socket cavity having a conical nose receiver portion with a relief vent allowing the oil/gas to escape through the valve assembly, when desired. The stop flow plug is shaped to fit within the inner socket cavity and moves between an open position and a closed position, wherein the stop flow plug fits securely against the conical nose receiver portion, sealing the relief vent. At the top of the valve, a nut will lock the stop flow plug to the close out plate for additional stoppage. A second embodiment adds a heavy duty insert to supplement the sealing pressure, when needed. Electronic monitors convey data remotely.