A compressor shroud assembly is disclosed comprising a dynamically moveable impeller shroud, a static compressor casing, an air piston mounted between said impeller shroud and said compressor casing, and a clearance control system. The air piston effects axial movement of said impeller shroud responsive to a supply of actuating air. The clearance control system regulates the pressure of actuating air in said air piston and comprises a supply conduit having a supply modulating valve and a discharge conduit having a blowoff check valve. The blowoff check valve is set to open at a predetermined differential pressure between pressure of the air piston and pressure of the supply of actuating air.