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.