A reusable continuously sealing metered dosing one-way valve assembly and delivery system flows a premeasured amount of a sterile flowable substance from a source which is coupled to an actuator assembly to an outlet orifice and prevents any backflow of contaminants through the continuously sealing one way valve assembly when the flowable substance ceases to flow. The valve assembly includes an elastomeric membrane which aids in preventing any backflow of contaminants when dispensing of the flowable substance is stopped. Multiple dosing of preservative-free flowable substance is provided.