Abstract: Apparatus for the preparation of gas mixtures includes cylinder which is divided into two chambers by means of a fixed central barrier. This barrier has a central orifice for receiving a rod which has central portion of diameter corresponding with the diameter of the orifice. The rod has end portions which pass through end plates of the cylinder and these end portions have a small diameter than that of the central portion, the diameters of the end portions being equal. A valved passage for the gases of either chamber to be transferred to the other chamber is provided in the barrier and a stepper motor is used to move the rod over small distances; with means to introduce or withdraw gas from either chamber.

Abstract: Apparatus for the preparation of gas mixtures includes cylinder which is divided into two chambers by means of a fixed central barrier. This barrier has a central orifice for receiving a rod which has central portion of diameter corresponding with the diameter of the orifice. The rod has end portions which pass through end plates of the cylinder and these end portions have a small diameter than that of the central portion, the diameters of the end portions being equal. A valved passage for the gases of either chamber to be transferred to the other chamber is provided in the barrier and a stepper motor is used to move the rod over small distances; with means to introduce or withdraw gas from either chamber.