Abstract: A valve for automatically modulating a flow of a stream of fluid, the valve including a housing having a wall defining an interior cavity. The interior cavity is in fluid communication with the stream of fluid. A modulator is mounted within the interior cavity and includes a shell in fluid communication with the stream of fluid and a flexible flow adjustment member within the shell. The flexible flow adjustment member has a variable diameter passage therethrough which is also in fluid communication with the stream of fluid. A circumferential void is located between the flexible flow adjustment member and the shell and a thermally reactive material is within the void and in contact with the shell for thermal communication therebetween. A tool is used to assemble the valve. The tool includes a base plate, and a receiver adjacent to the base plate. The receiver has an internal passage therethrough for receiving a segmented cone having at least one radial cut therethrough.