The air leaving the compressor is hot ,dirty ,wet and generally at a higher pressure than the down stream equipment requires . A typical 50 dm3/sec (100 scfm) compressor will push 4 500 liters of water and 8 liters of degraded compressor oil into the system in a year along with considerable amounts of dirt particles Before this air can be used it needs to be treated to remove the contaminants have its pressure reduced to the right level, and in many cases have oil added to lubricate downstream equipment. The accumulation of condensed water in the system can lead to pressure drop also .So Nowadays, most compressors have an after-cooler as a standard .fitting to perform the function of removing water, and some oil vapour. However, after coolers are also available as free standing units The after-cooler, through condensing, usually reduces the water content of the air by around 68% and uses approximately 2% of the total package power.