A valve assembly and fluid arrangement for continuous delivery of volumetrically proportioned gases or like fluids includes a valve assembly and a volumetric fluid storage bank, which has first and second sets of fluid storage chambers. The valve assembly alternately supplies a consumer with a blend of gases from the first set of fluid storage chambers while charging the second set of fluid storage chambers from pressurized gas sources, and, upon a threshold depletion of gases from the first set of chambers, supply the consumer with a blend of gases from the second set of fluid storage chambers while charging the first set of fluid storage chambers from the gas sources. Upon the threshold depletion of gases from the second set of chambers, the valve assembly again supplies mixed gases from the first set of chambers while charging the second set of chambers, and the process repeats.