Abstract: An anesthetic gas delivery system includes a gas machine for supplying anesthetic gas to a patient; a scavenging control system that controls a level of vacuum suction to evacuate waste anesthetic gas; and a user interface electronically coupled to the scavenging control system. The scavenging control system includes an air flow sensor external from the gas machine that measures the flow rate of the waste anesthetic gas through the scavenging control system; a control valve, such as a proportional solenoid valve, that is controllable to adjust the level of vacuum suction to adjust the flow rate of the waste anesthetic gas; and electronic control circuitry that is configured to receive a measured flow rate from the sensor and to control the control valve to adjust the level of vacuum suction based on the flow rate measured by the sensor. The electronic control circuitry further is configured to transmit flow rate information corresponding to the flow rate measured by the sensor to the user interface.