PUMP FOR ACCURATE MIXING OF 3 GAS COMPONENTS WITH PREDETERMINED FRACTIONS

A mixing pump that creates an accurate mixture of three gases at prede termined fractional ratios that can be set in steps of 10 ppm is descr ibed. A nearly continuous flow of each of the three component gases is produced by pistons driven by stepping motors; the gas mixture is for warded by a fourth piston. The flow of each component gas is adjusted by the stepping frequency of the motor and a microcomputer system is u sed to adjust the three frequencies according to the desired fractiona l concentrations. The total flow of the gas mixture is adjustable betw een 0.1 - 500 ml/min and is nearly independent of the after-load. The accuracy of the pump was tested by mixing the respiratory gases, O-2 a nd CO2, with various carrier gases (N, He or Ar) at various fractional ratios and total flow rates. The fractions of O-2 and CO2 in the mixt ure were analysed with the Scholander technique. In the physiological range, the mixing error in the gas fractions was less than 4%. The pum p is, thus, suited for producing calibration mixtures.