Water vapour (humidity-moisture) enters the air system through the air compressor inlet air filter. The air compressor sucks in approximately 7 cubic feet of atmospheric air at 0 psig, and that volume of air is compressed into 1 cubic feet of air at 100 psig. The water vapour (humidity-moisture) that was in the 7 cubic feet of atmospheric air is now compressed into 1 cubic feet of compressed air.
There are 3 forms of water in compressed air:
Liquid water is easily removed by general purpose line filters. They remove 98% of the liquid water and less than 10% water mist & 0% vapour.
Water in Aerosol or Vapour form requires the use of a Compressed Air Dryer.
For every 10°C drop in compressed air temperature, the moisture holding capacity of air is reduced by 50%.
Drying prevents liquid water forming downstream where it can contaminate or damage the system causing operating problems, costly maintenance, and repairs.