The outflow of air from a compressor contains excess moisture from condensation, heat from the compression and dirt from various contaminating particulates. If this contaminated air were to go directly into such downstream equipment as valves, hoses and cylinders, it could damage these components and reduce their useful working life. Therefore, the compressed air must be filtered, regulated and also lubricated before it can be used.
Filter regulator units are the solution to cleaning compressed air. The filter is the first item in the air line when the air exits the compressor, and it is designed to strain the air in order to trap solid particles such as rust, dust and dirt. The filter can also separate out any liquids (oil as well as water) that may have been generated or mixed into the compressed air. After the filtration, the cleaned air passes to a regulator, which reduces and controls the pressure in the air flow, often by means of an exhaust vent. A regulator should ideally maintain an unvarying output pressure, whatever the input pressure and output flow required. Regulators do need to be correctly sized for the desired application, and in most cases a lubricator will also be installed which reduces friction in moving components. The correct size of filter also needs to be determined for each application, according to the maximum pressure drop permissible by the filter. Manufacturers commonly provide flow curves and characteristic charts to assist in determining the appropriate sizing.