1. With reference to basic constructional features, contrast the methods of compression employed by positive displacement and dynamic air compressors.

2. An item of plant requires 2 m3 min-t of pulsation-free and oil-free compressed air supplied at a pressure of 7 bar. Select and size a suitable type of machine with regard to output FAD (free air delivered) and quality of air supply.

3. Air is drawn into a compressor at normal temperature and pressure (N.TP.) and compressed to a pressure of 6 bar gauge. After compression the air is delivered at 1.2 m3 min-t and cooled to a temperature of 30°C, at which point condensate is collected at the rate of 2 litres per hour. Estimate the FAD (N.TP.) of the compressor, and the relative humidity of the air entering the compressor.