Abstract: A parenteral liquid infusion set comprises flow tubing, and means for connection to blood vessel penetrating means and a parenteral liquid source at opposite ends thereof. A drip chamber is present in the set having a tubular drop-forming member of reduced inner diameter. An intermediately positioned site is present for providing access to the interior of the set from the exterior, the site being positioned downstream from the drip chamber. In accordance with this invention, a portion of the fluid flow tubing downstream from the connection site defines a bore of reduced diameter, when compared with the remainder of the flow tubing, to prevent the creation of a less than atmospheric pressure in the set and to prevent air from being sucked into the flow tubing through an administration set connected at the intermediately positioned site.

Abstract: A twin check valve pumping system for use with a syringe or other variable volume pumping device for the pumping of liquids. Along a flow path between the check valves, a porous, hydrophobic member is positioned, in communication with a portion of the flow path upstream of the first, inlet check valve. The second, downstream outlet check valve is biased so that pressure in the conduit between the check valves is required for expulsion of liquid. When gas enters the system, such pressure cannot be achieved, because, upon attempted pressurization of the area between the two check valves, the gas passes through the porous, hydrophobic member back to a position upstream of the first, inlet valve. However, aqueous liquids cannot pass through the porous member, and accordingly the device pumps such liquids normally in the absence of gas.