In pneumatic technology, assembling air filters, pressure reducing valves, and oil mist devices together is called a pneumatic triad, which is used to purify, filter, and reduce the pressure of the air source entering the pneumatic instrument to the rated air source pressure supplied by the instrument, equivalent to the function of a power transformer in the circuit. The air filter pressure reducer is designed to be lightweight and easy to install, so it is installed together with pneumatic transmitters, pneumatic regulators, valve positioners, and other products for use. If the air filter and pressure reducing valve are designed as a whole and become a two-piece component.