An air bleeder (MAC) valve is just a small air pressure control regulator that fits onto the bottom of the airbrush. It has a small black screw on the side that allows you the freedom to make real-time air adjustments in minute portions while you are spraying the makeup. It completely eliminates the need to reset or dial down at the air compressor end. It works from fully open to fully closed, allowing the full range of pressure from the compressors output capability. As the photo above demonstrates, one end of the valve threads onto the airbrush hose and the other end has a quick disconnect feature that slips onto the air valve stem on the bottom of the airbrush. Using this MAC valve enables you to run your compressor at a slightly higher air pressure than you normally would, then adjust the operating pressure you desire down to the ideal spray volume you desire right through the airbrush the MAC valve. When you fully open the MAC valve the airbrush can be quickly discharged of residual makeup, and also faster cleaning and rinsing between color changes.