Many miniature vacuum pump itself is not the function of adjusting the degree of vacuum. Only by adding the valve way to adjust. For example, the pump suction side string a precision pressure relief valve, when the vacuum is high, the valve is opened, the vacuum on the down. This pressure relief valve also has a directional discharge of toxic gases, etc., to the designated container channel, which is a lot of valves do not function. If you want to be simpler, you can use the smart vacuum pump, the pump has a button above, you can set the negative pressure, as well as negative pressure LCD panel display. In addition there is a knob, you can adjust the flow of large and small. This smart vacuum pump, also known as AC vacuum pump, digital vacuum pump.