This is a Jetstream jet body for Hot Spring hot tub models from 1991-1993 and 1997-current. Also for Tiger River hot tub models from 1997-current.
The Jetstream is a powerful jet that combines the pressure of several jets into a substantial stream. The Jetstream is located in the footwell of the spa to provide a massage to the feet and calves.
The air control valve is used to control the intensity of the Jetstream. To adjust the intensity, turn the air control lever clockwise to increase the intensity (air), or counter-clockwise to decrease the intensity (air).