In the present contribution a physical model of the flow occurring inside impulsive actuators is developed. An impulsive actuator is characterized by its sudden flow output. The subsonic actuator under consideration is composed of a high pressure air supply and a sonic orifice driven by a valve and followed by a tube. A theoretical analysis is put forward and assessed using experimental data. It is demonstrated that the operation of such actuators essentially depends on a single parameter consisting of the reservoir to ambient pressure ratio and the throat to tube area ratio. The relationship between this parameter and others, such as the length to diameter ratio of the tube are explored. In the unsteady mode the flow inside the tube is thoroughly analyzed with the help of measurements at the exit of the tube. In addition, the time scales involved are accurately extracted, which is a crucial factor in designing closed-loop control approaches. The results obtained therefore provide an important design tool for engineering problems in flow control. Results are also applicable in the more general context of fluidic networks containing a sonic nozzle.