Rule of Thumb

Rule of Thumb

* At an ambient temperature of 75°F and 75% relative humidity, a typical 500 scfm air compressor takes in 90 gallons of water vapor every 24 hours. Discharging air at 100°F and 100 psig, a well-maintained after cooler may remove about 57 gallons. That leaves 33 gallons inside your air system. Producing a 38°F dew point a refrigerated dryer removes an additional 29 gallons.

* One cubic foot of air at atmospheric pressure contains:
— Liquids – Water droplets
— Solids – Dust and pipe scale
— Gases – Oil and water vapors

Once atmospheric air passes through a compressor operating at 100 psig, the air is compressed to 1/8th its previous volume, yet still contains the same amount of contaminants. The increase in pressure would normally cause moisture to condense out of the air, however, during the compression process, the temperature of the air rises due to frictional heat, increasing its ability to hold water vapor.

As air leaves the compressor and travels throughout the system, it begins to cool. Once the air temperature drops below the pressure dew point temperature, water droplets begin to condense. It is necessary to remove the moisture and contaminants from the air system in order to lower the dew point and avoid operating problems, costly maintenance, and repair expenses. Water vapor and other contaminants in the ambient air enter the compressor intake.