An air volume regulator adapted for use in an air distribution system for maintaining a constant flow of air therethrough regardless of variations in pressure of the air being supplied to the regulator is provided with adjustment means to permit adjusting the regulator for maintaining constant flow at a variety of different flow rates. The regulator includes a housing defining a passageway for the flow of air therethrough, valve means movable within the housing for adjustably restricting the flow of air therethrough, and a coil compression spring cooperating with the valve means for exerting an opening bias thereon in opposition to a closing bias imparted on the valve means by the pressure of the air in the housing. Adjustment means is provided cooperating with the coil spring for immobilizing a selected number of the turns of the coil spring so as to vary the biasing characteristics of the spring and thereby adjust the regulator for maintaining a different flow rate.