Abstract: A metering pump for providing relatively small, precise volumes of fluid is provided. The pump piston and/or the interior of the cylinder has a surface finish exhibiting a roughness average within selected limits and a vapor deposited polymer such as polytetrafluoroethylene. A drive mechanism is provided for simultaneously rotating and reciprocating the piston within a cylindrical chamber. Fluid is thereby drawn into the chamber and expelled. The pump can be employed in a dialysate circuit or other fluidic circuits containing crystal or other residue-forming fluids, obviating the need for pump wash ports.

Abstract: In a hemodialysis system including a dialyzer having a semi-permeable membrane, apparatus for accurately proportioning and mixing fluids comprising a double acting piston/cylinder unit of which the cylinder is divided into two chambers by the piston and the volume of the cylinder swept by the piston at one end of the piston is lesser than that at the other end. An inlet connection for first liquid is made to one chamber, a conduit connects the two chambers and includes a connection to a source of the second liquid. Valve means are associated with the conduits and are effective to cause a charge of first liquid to be delivered to the one chamber and thereafter to be transferred to the other chamber, drawing liquid from the source of the second liquid to make up for the difference in volume. Said valve means then cooperate to cause the mixed liquids to be discharged from the other chamber as said one chamber is again charged with said first liquid.

Abstract: Apparatus for exposing a fluid to a negative pressure particularly for degassing liquid containing a gas comprises a double acting piston/cylinder unit of which the cylinder is divided into two chambers by the piston, the volume of one chamber swept by the piston being lesser than that swept by the piston in the other chamber. An inlet for a fluid is made to said one chamber, a conduit connects the two chambers and an outlet is made from the other chamber. Valve means are associated with the conduits to permit controlled reciprocation of the piston within the cylinder and fluid passed from said one chamber to the other is exposed to a negative pressure in the other chamber, gas, in the situation in which the fluid is a gas-containing liquid, forming bubbles in the other chamber or, where the fluid is wholly liquid, a part of that liquid being vaporized.

Abstract: Apparatus for accurately proportioning and mixing fluids comprising a double acting piston/cylinder unit of which the cylinder is divided into two chambers by the piston and the volume of the cylinder swept by the piston at one end of the piston is lesser than that at the other end. An inlet connection for a first fluid is made to one chamber, a conduit connects the two chambers and includes a connection to a source of the second fluid. Valve means are associated with the conduits and are effective to cause a charge of first fluid to be delivered to said one chamber and thereafter to be transferred to the other chamber drawing fluid from said source of second fluid to make up for the difference in the volumes of the chambers. Said valve means then cooperate to cause the mixed fluids to be discharged from the other chamber as said one chamber is again charged with said first fluid.