Yes, the pump will fill/pressurize the extraction vessel up to the set point. If there is no flow of material out of the vessel, the pump will shut off. As soon as the variable restrictor is opened, dissolved materials (analyte) and carbon dioxide begin to flow out of the pressure vessel. The pump will begin to actuate to maintain a pressure set point. Think of the restrictor as a Back Pressure Regulator. As you adjust the restrictor to various flows, the pump will speed up or slow down accordingly to maintain the overall system set point pressure.