Abstract: A method and an apparatus for controlling the flow rate of a fluid are disclosed. Fluid is flowed through an elongated passage having a small cross-sectional area to control the flow rate thereof. The length of the elongated passage through which the fluid is flowed is changed in a predetermined manner to change the flow rate of fluid. The apparatus comprises a first member having a spiral shaped elongated groove with a small cross-sectional area formed in a surface thereof and a second member having a surface overlying the groove to form the elongated passage for controlling the flow rate of the fluid.