The purpose of filtering compressed air and gases is to remove or decrease amount of floating pollutant. Coalescent filters of Parker domnick hunter are decreasing dust and oil content in two steps. First grade decreases dust content uder 1 micron size and oil concentration under 0,6 mg/m3. Second grade reduces these values to 0.01 micron and 0.01 mg/m3 respectively. It means, compressed air after this treatment can considered class 1.1. by ISO 8573-1:2010 standard. If application is critical regarding residual oil content, there is an option to apply Oil Vapour Removal (OVR) unit, which can reduce it under 0,003 mg/m3.