A method of making a membrane for use with a flow control system is disclosed. A female mold body portion and a male mold body portion are provided. A body portion support member configured to receive at least a portion of the female body portion and at least a portion of the male body portion is provided. The female and male body portions are separated from one another Membrane manufacturing material is provided to a concave portion of the female mold body portion. The sleeve is moved downward. The lower mold portion is lowered until it is just short of its final intended position. Excess membrane manufacturing material, if any, is removed from around the seam of the mold. The upper mold portion is lowered the remaining distance so that the two mold portions are separated by the exact distance desired for the final membrane thickness.