A rotary solenoid actuator for proportionally controlling the flow of fluid, such as air, in a pipe comprises a housing with a rotor rotatably mounted thereon. A stationary coreless coil for generating a magnetic field in response to a control current therethrough is mounted in the housing. A permanent magnet is affixed to a rotatably mounted shaft within the coil, and a return spring is attached to the rotating shaft. Due to low hysteresis in the coreless coil, there is a linear relationship between the control current and the fluid flow.