The constant flow function of the air volume control valve is achieved through the contraction and expansion/retraction of the silicone capsule located in the center of the balancer. The principle is an internally adjustable cross-sectional area silicone capsule that automatically adjusts the cross-sectional area during changes in wind pressure and volume, maintaining stable airflow within a wind pressure range of 50-200pa and high pressure from 150-600pa. The air volume control valve also serves to reduce noise. It effectively reduces wind noise in ducts, particularly in the exhaust systems of hotels and office buildings, replacing exhaust fans, and can significantly lower noise, save energy, and maintain continuous ventilation.