This note describes the design and performance of a pulsed valve developed as a gas source for a 500 mm long supersonic Laval nozzle with a 3 mm wide throat. The valve consists of a rotating drum with a slit, which allows an opening duration of approximately 14 ms. The duration of quasi‐steady‐state expansion is measured to be 10 ms at the nozzle throat when the pulsed valve is filled with 200 Torr of Ar gas.