The invention relates to a valve assembly for use in connection with carpet cleaning extraction machines and similar extraction cleaning devices. The invention allows the intake of liquid and the mixing of different liquids in a mixing chamber, such as clean water with detergent, and the discharge of a selected liquid without the formation of an air or vapor lock that would inhibit the discharge of the selected liquid. In particular, the invention prevents the formation of a vapor lock when water is being drawn into a chamber that would prevent the subsequent discharge or spraying of the liquid.