Abstract: In-line valve means for isolating a source of fluid under pressure from a desired using apparatus until use of the fluid is desired. The in-line valve means includes a positively sealed plug and an on-off isolation control valve which is positioned by appropriate electromagnetic means such as a torque motor or a solenoid. The plug has a frangible area which is sheared by forces generated by the electromagnetic force motor. After the plug is sheared it is positioned by appropriate means within the flow path to preclude substantial interference with the flow of fluid from the source through the control valve to the outlet. Subsequent repetitive on-off control of the fluid may be accomplished with a second seal and seat in series with the positive seal plug and actuated by the same electromagnetic means.