Diffusion barrier in a delivery apparatus for pressurized medical liquids
A delivery apparatus for pressurized medical liquids has a reservoir for medical liquid and a pressurizing means configured for pressurizing medical liquid to a driving pressure; with a diffusion barrier arranged to float on medical liquid in the reservoir and disposed to cover substantially the entire surface of the medical liquid in the reservoir for the purpose of preventing diffusion of gas present in the reservoir into the medical liquid.
1. A delivery apparatus for pressurized medical liquids, comprising:
a reservoir containing a medical liquid within an inner wall of said reservoir, said medical liquid having a continuous liquid surface in said reservoir, and a pressurizer that pressurizes a gas above said liquid surface in said reservoir the medical liquid, said reservoir having an upper portion above said continuous liquid surface and a refill inlet disposed in said upper portion allowing refilling of said reservoir with medical liquid, and said reservoir having an outlet located below said liquid surface and a controllable valve in fluid communication with said outlet that controls discharge of said medical liquid, forced by said pressurizer, via said outlet; and
a diffusion barrier that floats unrestrained on the liquid surface on the medical liquid in the reservoir, said diffusion barrier having size that covers said liquid surface of said medical liquid in said reservoir except for a peripheral gap between said inner wall and said diffusion barrier in a range between 0.1 mm and 1 mm, and said diffusion barrier being comprised of a material that, in combination with said size of the diffusion barrier, prevents diffusion of gas in the reservoir into the medical liquid.
2. A delivery apparatus as claimed in claim 1 wherein said pressurizer applies a pressurizing gas to said surface of said medical liquid in said reservoir.
3. A delivery apparatus as claimed in claim 1 wherein said diffusion barrier comprises a horizontal cross-section substantially corresponding to a horizontal cross-section of the reservoir.
4. A delivery apparatus as claimed in claim 1 wherein said reservoir has a cylindrical shape and wherein said diffusion barrier has a shape corresponding to a convex lens.
5. A delivery apparatus as claimed in claim 1 wherein said diffusion barrier has a peripheral section having a vertical cross-section shaped as a segment of a circle having a radius smaller than a radius of a horizontal cross-section of the reservoir.
6. A delivery apparatus as claimed in claim 1 wherein said diffusion barrier has a peripheral section forming a thin ring with a hard edge around said diffusion barrier.
7. A delivery apparatus as claimed in claim 1 wherein said diffusion barrier has a circumferential peripheral section that defines a plane, and a center of gravity located below said plane.
8. A delivery apparatus as claimed in claim 1 wherein said diffusion barrier comprises a surface treatment that reduces a surface tension of said diffusion barrier to promote transport of bubbles in said medical liquid from beneath said diffusion barrier.
9. A delivery apparatus as claimed in claim 1 wherein said reservoir forms a main reservoir of said delivery apparatus.