Hot compressed air coming from Air Compressor cannot be used directly in most applications. It is therefore cooled to a temp of around 40o C, which is done in the Aftercooler.
This is a shell & tube type Heat Exchanger where compressed air in the shell is cooled by plant cooling water circulating in the tubes. The liquids which condensed due to cooling are separated by the in- built Moisture Separator. Draining can be done manually or by Auto Drain Valve.