Compressed Air Best Practices - April 2008 - (Page 34)

| 04/08 Focus Industry PLASTICS BLOW-MOLDING | BY DOCTOR VACUUM Where there is flow, there is restriction. Vacuum systems are not an exception to this rule and it is important to know how restricted airflow, through a vacuum distribution system, can affect your energy bill. A little known fact is that pressure differential, also called pressure loss, is the single largest contributor to elevated energy input in vacuum systems. Maintaining pressure differentials within reasonable limits keeps your vacuum system operating costs in line with industry norms. Pressure differential is simply the difference in vacuum from the point of use to the inlet of the vacuum pump. As air (or any other gas) flows through a distribution syste m, there is friction along the inner pipe walls that creates pressure differential. In addition to the pipe itself, other components can and will contribute to the overall problem. Inlet filters, point-of-use filters, receivers, condensers, isolation valves and check valves can all be suspect especially if any of these components are undersized or misapplied. Undersized inlet filters or inlet filters that are loaded with particulate are especially notorious for adding differential and in vacuum systems it is not always evident that an issue exists. Also note that 90º elbows, pipe T’s and pipe reducers are necessary to some degree but can magnify the condition when used in excess. Calculating the total pressure differential is easy — take the reading at the inlet to the vacuum pump and subtract the reading at the point-of-use to get the aggregate pressure loss. Much more difficult is defining which individual components contribute most to the vacuum loss and even more significant is determining how to correct each component in a way that makes economic sense. This last statement is most important because it is not prudent to make expensive corrections to a distribution system that will provide only marginal returns. It is essential to identify and repair only those issues that can boost productivity and reduce superfluous energy expense. Systems that operate at higher vacuum will have more waste in energy cost as a result of pressure differential than systems that operate at lower vacuum. This is not to say that low vacuum systems cannot be optimized, only that the relative effect is greater at the higher vacuum levels. For example, if we compare the additional operating costs for a 3" HgV pressure differential in three different vacuum systems operating at cascading vacuum levels we can easily calculate the additional flow requirements. Note that a 3" HgV pressure differential is very common in real world production vacuum systems. Let’s assume that the three systems are operating at 12" HgV, 20" HgV and 24" HgV respectively. The 12" HgV system will require the supply vacuum pump CO2 O Pressure differential, also called pressure loss, is the single largest contributor to elevated energy input in vacuum systems. 34 www.airbestpractices.com kW http://www.airbestpractices.com

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Compressed Air Best Practices - April 2008 Contents From the Editor Utility-Air News The Compressed Air Audit of the Month: Minimizing Blow-Molding Pressure Fluctuations AF Compressors: Focused on 40 Bar, Oil-Free Air for the PET Industry Real World Best Practices: PET Plants Using Boosters for High-Pressure Air Guaranteeing Audit ROI for Blow-Molders Managing Vacuum Pressure Differential Are You Taking Full Advantage of Pneumatic Valve Technology? Are You Strategic? Resources for Energy Engineers: Training Calendar & Product Picks Wall Street Watch Advertiser Index Job Market

Compressed Air Best Practices - April 2008

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