In the event that you have an application for compressed air that requires that the pressure to that application to change, you can regulate the air pressure manually by turning the knob on the air pressure regulator.
The typical DIY home compressor will usually be equipped with a regulator that controls the air pressure leaving the compressor to the application. It should also have an air gage on it, that shows you what the pressure will be downstream from that regulator.
The compressor tank will also have a pressure gauge to show you what the air pressure is upstream from the regulator.
Remember, you cannot dial-up a pressure higher than that which is in the tank.
Posted by Bill 