An improved air volume regulator used in HVAC operating at a static pressure below 25 pa. (0.1''w.g.) having a pair of opposing gates facing into the airflow and a V shaped baffle positioned to form two constricting passageways. Air flowing through the passageway generates a light vacuum at its throat and combined with the static pressure differential across the gates urges them towards the baffle and constricts the airflow. A counterbalance spring cooperating with a concave cam and cam follower applies a resisting bias on gates such that the airflow in the regulator remains constant under varying inlet conditions. A variable spring rate mechanism permits the adjustment of the airflow rate over the full operating range using a single counterbalance spring. A cable driven "limited torque" flywheel controls the air volume regulator's propensity to pulsate under unstable inlet airflow conditions.