Compressed Air Best Practices - November 2008 - (Page 24) | 11–12/08 Compressed Air Industry STEEL & METALS | E N E R G Y- E F F I C I E N T C O M P R E S S E D A I R P I P I N G S Y S T E M S Metals can also degrade. Copper and black iron have been the overwhelming favorites for compressed air systems for many years due to the cost of the materials. However, threaded joints often serve as a source of leakage. This leads to higher operating costs because compressors must operate overtime to compensate for the leakage. But these aren’t the only drawbacks to metal piping systems. Interior corrosion can cause scaling and pitting on inside surfaces. As the corrosion products combine with moisture and other contaminants, they accumulate on the inner surfaces of the pipe and fittings, increasing their roughness. As the internal diameter becomes rougher, pressure drop increases. Again, this ends up costing money by reducing efficiency of the compressed air system. Perhaps more importantly, particles can dislodge and clog or damage end-of-line equipment. Lightweight aluminum is the ideal product for maximum flow. The first push-to-connect aluminum piping system was launched by Legris in 1996. Transair is a system of powder-coated aluminum pipe and engineering-grade polymer connectors. Transair’s quick, instant connections eliminate the need to thread, solder or glue pipe. The lightweight aluminum pipe is also easy to handle and safe to work with on elevated platforms. The flow characteristics of Transair’s smooth bore aluminum pipework are crucial in helping to reduce the pressure loss through the system. Each stick of pipe and each take-off to a component such as an air tool will cause a reduction in pressure. For maximum system efficiency, Transair connectors do not intrude into the pipework to cause turbulence nor do they cause scratching on the outside of the pipe, which can cause a leak at each connection. Push-to-connect aluminum piping. Pipe Sizing The cost of air mains frequently represents a high proportion of the initial cost of a compressed air system. Therefore, smaller diameter pipe is often specified to save on capital cost. However, this is misleading since the restriction due to the smaller piping causes greater pressure drop across the system, resulting in higher energy consumption. The increased energy costs can soon exceed the price of larger diameter piping. This graph shows what happens to the power required to deliver 29 scfm of seven 102 psig air along 328 feet of steel pipe as the diameter changes. As a general rule, pipe diameters should be calculated based on having a maximum air velocity of 19 ft/s, in the main supply line. In branch lines with a total length less than 49 feet, velocities up to 49 ft/s are acceptable. 24 www.airbestpractices.com http://www.airbestpractices.com
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