The invention relates to a process and apparatus for delivering an ultra high purity fluid comprising at least one component to a point of use at a required pressure without mechanical pumping. In one embodiment, a high purity feed comprising at least one component in gaseous or liquid form is charged into a vessel and at least partially converted to a solid phase source. As the feed is converted to a solid phase source, additional feed may be added until the vessel is at least substantially filled with a solid phase source or slush. Once filled, the solid phase source or slush may be isochorically heated whereby the solid phase source is converted to a product at an elevated pressure.