An Investigation of the Behavior and the Controllability of an Inspiratory Valve with Reversed Flow

Sammanfattning: This master thesis is performed in collaboration with Maquet Critical Care, Solna, Sweden. Maquet Critical Care is one of the leading ventilation and anesthesia machine producers in the world. The purpose of this master thesis is to investigate the feasibility of a new concept of gas mixing valve, namely "a valve with reversed flow". This valve is more energy efficient, inherently safer and has possibly lower cost than regular valves used currently in medical ventilators. The thesis is mainly divided into three parts. First, preliminary experiments were made to understand the force and flow characteristics of the valve with the reversed flow. A valve structure, on which reversed flow can be applied, was designed for these experiments. Secondly, SolidWorks flow simulations were made to decide the diameter of the valve seat. A mathematical model was developed to represent the valve system and validated with the valve prototype produced for the preliminary experiments. Finally, a PI flow feedback controller was designed to test the controllability of this valve. The controller was implemented both in the simulation environment and on a real valve. The results of the experiments reveal that the valve with reversed flow is feasible for the use in medical ventilators.