Relative Humidity is the ratio of moisture in the air compared to the capacity of moisture that volume of air is capable of holding at a specified temperature. When air is compressed, friction causes the actual air temperature to rise, greatly increasing its ability to hold moisture. At 100 PSIG the quantity of moisture commonly held in eight cubic feet of air is reduced in an area 1/8 its original size. The result of compression is hot, wet, dirty air.
                                                                                                                                      A good general rule is that for every twenty degrees Fahrenheit (20°F), the temperature of air decreases, its ability to hold moisture is reduced by 50%. As air passes through a plant piping system, the ambient conditions cause the compressed air to cool, causing the formation of liquid water. This water, coupled with particulate matter and oil/lubricant carry-over will cause numerous problems. The water will wash away lubricants from tools and machinery, spoil paint applications, rust the general system, and, if exposed to unfavorable ambient temperatures, freeze. Particulate matter will clog orifices and valves, damage gear driven equipment, increase system pressure drop and contaminate product. Residual oils and lubricants will cause valve wear, spoiled product and system contamination. It is essential to treat process air before it can do any damage. By drying and filtering compressed air, operation efficiency can be maximized, and equipment productivity and longevity greatly increased. A properly designed air system will pay for itself.