Gas separation is generally composed of a primary separation of oil and gas barrels and a secondary separation of oil and gas separators. Most of the oil in the oil and gas mixture falls to the bottom of the tank under the action of centrifugal force and gravity, and the compressed air containing oil mist (suspended oil particles below 1um in diameter) must be filtered through the micron and glass fiber filter material layer of the oil and gas separation filter. The oil particles are directly intercepted by the filter material and the mechanism of inertial collision condensation, so that the suspended oil particles in the compressed air quickly condense into large oil droplets, and the oil gathers at the bottom of the oil core under the action of gravity, and returns to the main engine lubricating oil system through the secondary return pipe inlet at the bottom recess, so that the air compressor can discharge more pure and oil-free compressed air.