A sealed delivery system for dispensing metered volumes of a pure or sterile flowable substance is presented. In exemplary embodiments of the present invention, a hand-held sealed delivery system comprises a continuously sealing one-way valve assembly at a distal end, and a volume reducing reservoir at a proximal end. The pure or sterile flowable substance can be stored in the volume reducing reservoir. In operation, a user pushes down upon a push button driven actuator assembly, acting upon a metering pumping chamber, which is in fluid communication with the pure or sterile flowable substance stored in the volume reducing reservoir via a check valve. Depression of the push button driven actuator causes a dispensing pump to push a metered volume of flowable substance through the continuously sealing one way dispensing valve assembly. Return of the push button driven activator to its home state causes the dispensing pump to pull a metered volume of the contained flowable substance from the volume reducing reservoir and through the check valve. In exemplary embodiments of the present invention, a continuously sealing one way dispensing valve assembly prevents any backflow of contaminants through the dispensing orifice when the flowable substance ceases to flow, while the materials and sealed assembly of the overall dispensing delivery system prevent other means of contamination of the remaining pure or sterile substance contained within. In exemplary embodiments of the present invention, one or more components of the continuously sealing one way dispensing valve assembly, or of the delivery system general, can be bacteriostatic, bactericidal, or both.
