AIR TECHNOLOGY GROUP PTY. LTD.

THE GOLDEN RULES FOR COMPRESSED AIR APPLICATIONS

1. The 8oC Temperature Rise Rule The life of both motor winding insulation and compressor lubricants is reduced by 50% when either item is run continuously at 8oC above it’s design temperature. 2. The 7oC Water Vapour Rule Every 7oC change in the temperature of air diminishes or increases the water vapour content by 50% (temperature rise increases water content). 3. The Power vs Pressure Rule Every 2 psig (13.8 kPa) pressure change equates to 1% of power drawn by a compressor (so raising pressure from 100 psig to 102 psig (700 kPag to 714 kPag) increases power consumption by 1%). 4. The Volume vs Pressure Rule In the pressure range of 100-120 psig (700-827 kPag), every 1 psig (6.89 kPa) pressure change equates to a change in the compressor’s flowrate of 0.00075 times the nominal flow (i.e. a rise of 10 psig in pressure decreases the flow rate by 10 x 0.00075 x rated flow rate ). [note: Pressure rise = Flow decrease]

Flow Rate Change = Nominal Flow Rate x Pressure Change x 0.00075

5. The Cost of Pressure Drop Rule Every 2 psig (13.8 kPag) pressure drop uses 1% of the connected power (i.e. a 10 psig (68.9 kPag) pressure drop across a filter element costs 5% of the total compressor power to overcome it and still maintain the set pressure). 6. The Pressure Dewpoint Rule The pressure dewpoint is the temperature at which water vapour will start to condense at the stated pressure (e.g. air dried to 3oC pressure dewpoint at 100 psig (700 kPa) will not discharge any more liquid water unless the temperature of the compressed air falls below 3oC). As a helpful rule of thumb, compressed air leaving an air dryer at a pressure dewpoint of 1.6oC has had it’s water vapour content reduced by 90% from the saturated condition in which it left the air compressor. 7. The Pressure vs Output Rule Air tools are designed to operate at maximum efficiency at 90 psig (620 kPag) and if the air pressure in the supply system is less than that, the tool efficiency falls quickly. At 70 psig (482 kPag), the efficiency of an industrial airtool is 37% less on average than at 90 psig. So a useful rule of thumb is that airtools lose 20% efficiency for every 10 psig (69 kPa) drop in system pressure below 90 psig (620 kPag). Raising system pressure will increase airtool productivity (but also increase the wear rate).