Compressors Standard Air Standard air has the following characteristics 14.7 psia (101 kPa abs) Density lb/ft 3 (11.8 N/m 3 ) Temperature 68 F (20 C) Relative humidity 38% Pressure lower than 14.7 psi (101 kPa) absolute creates a vacuum pressure Rating Compressors Compressors are rated in terms of cfm or scfm when the inlet is drawing from atmospheric conditions (101 KPa, 20 o C) (14.7 psia and 68F ) Compressors While air enters at ambient conditions it must be converted to operate at pressures of 6 to 12 bars, and temperatures of C When conversion takes place it produces variation in the pressure, temperature, and volume (typically it is reduced) Compressor Categories Positive displacement Piston, Screw, and Vane Compressors having more than one cylinder are called multi-stage; the pressure increases are done through the use of multiple cylinders to achieve desired pressure Power requirements How much horsepower do we need to run the system? Q(sm3/min) P(kPa Abs) Compressor types Single cylinder compressor Multi-staging Up to 4 barsingle stage Up to 15 bardouble stage Over 15 bartreble or multi-stage Two-stage compressor Multi-staging with inter-cooling for high pressures Screw compressors Vane compressor Receiver pressure control via motor start/stop Compressor unloading pressure switch Compressor unloading centrifugal unloader Pressure settings Conditioning Air The key components to condition compressed air are: coolers Moisture separators Air dryers & receivers Filters, regulators, lubricators Mufflers Conditioning components After coolers Used to condense moisture in air prior to operating components (80-85% effective) Moisture separators Used to collected and discard condensation from air Air dryers Secondary measure used to extract any remaining moisture from system (uses desiccants) Conditioning components Air receivers Storage vessel used to equalize the pulsation of incoming air and allow for uniform flow or air Filters, regulators, lubricators Used to clean, regulate, and lubricate Mufflers Placed at exhaust to reduce noise and the possibility of airborne particles Moisture and Dew point Depending on atmospheric conditions air will contain varying degrees (percentages) of moisture Saturation point (dew point) is the temperature at which moisture begins to condense of the air