A method for controlling flow and concentration of a liquid precursor includes: supplying a carrier gas to a first auto-pressure regulator and outputting therefrom the carrier gas at a first pressure to a precursor reservoir; outputting the mixture of the vaporized precursor and the carrier gas from the precursor reservoir; and supplying the mixture to a second auto-pressure regulator and outputting therefrom the mixture at a second pressure to a reactor via an orifice.