The air in the atmosphere contains moisture which increases with temperature. The suction of moist air by the compressor means the moisture in the air enters the air line and to the pneumatic devices from there.
  

   The possible consequences of condensation of moisture in the compressed air installation is corrosion in the air lines and pneumatic devices and the  formation of a gum like residue of the dust in the sucked air and oil from the compressors with the moisture. This residue may cause narrowing of cross sections which results in resistance in the pressure air lines. In addition, it may clog the pneumatic circuits and adversely affect the operation of the device.

    Main problems that may arise in compressed air lines and pneumatic devices is the increase of product faults as the result of (non-)operation of control systems correctly and at expected speeds and the increase of maintenance costs for air lines and pneumatic devices. For this reason the air exiting the compressor needs to be dried.

   With these filters that may be used especially after oil injection compressors, a significant portion of the oil coming from the compressor can be captured. Thus the problems oil may cause in the product and the pneumatic circuits can be avoided. At the same time the accumulation of the oil from the compressor in the air lines and causing both dirt and cross sectional reduction and consequently pressure losses are avoided.

Oil and Dust Filters

  
   Filters used for dust and oil are offered as pre-filter and sensitive filter. The efficiency of filters depends on the temperature of compressed air and their efficiency ratings are generally given for 20◦C compressed air. For this reason, the conditions the  efficiency figures are based on must be noted. Pre-filters can capture dust and particles up to 1 micron. The amount of oil in the compressed air after this filter is approximately 1 ppm.

   Sensitive filters, on the other hand can capture down to 0.01 microns of dust and particles. The amount of oil in the compressed air after these filters falls to 0.01 ppm level. On these filters are indicatoırs showing the pressure loss due to clogging. Even though the pressure loss does not reach the max. level it is recommended that the filter internal component is replaced minimum once a year.

  
  These filters are used after the filters for dust and oil to reduce the amount of oil to lower levels and remove hydrocarbon smells. In case the compressed air temperature is 20 °C the amount of oil remaining after these filters will be around 0.003 ppm.

  Before these filters the dust and oil filters should be definitely used. Even though they can reduce the amount of oil to very low levels they cannot filter at all after they reach saturation. As the water completely pours from a sponge which has completely been wetted with water, the oil entering the filter totally exits from the filter.