A Pyrotechnic valve is a one time use propulsion component often used to control propellant or pressurant systems on spacecraft. The device is activated by an electric signal, to fire a small explosive charge which in turn shears away a small flange that initially blocked the flow path of the attached tubing. Another version of a pyrotechnic valve remains in an open position until activated. The pressure from the pyrotechnic charge then forces the flange into a weakened part of the attached tube to block the flow path of the tubing.
These two versions of pyrotechnic valves are referred to as normally-closed (NC) or normally-open (NO) valves, depending on their initial state before initiation of the pyrotechnic charge.
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Pyrotechnic valves Wikipedia(Text) CC BY-SA