Compressed Air Best Practices - October 2008 - (Page 57) Compressed Air Industry AUTOMOTIVE TRANSIT | 10/08 | run at 98 psig or higher.” When you hear these words, what is the supervisor really telling you? In this case, when the system header pressure falls below 98 psig, the grinders don’t work well. Production personnel did not know the actual pressure at the tool or how much air the tool uses. The rest of the plant could have run at 80 psig, but it ran at 98 or more because the grinding area supposedly required it. Furthermore, grinding accounted for only 20% of the demand, so 80% of the plant was supplied with air at a much higher pressure than needed. The higher pressure throughout the plant amounts to thousands of dollars a year in increased energy (6%) to produce and increased flow (15%) of all unregulated air throughout the system. Testing with a “needle gauge” at full operation revealed that the actual inlet pressure to the tool was 63 psig at load, but the header pressure stayed at 98 psig. In other words, a 35 psig pressure loss occurred through the plumbing between the header pipe and each grinder. Further testing revealed that the grinders needed only 75 psig for optimum performance at this specific process. In this case, operators felt the recommended 3⁄4" hose to be too heavy, so 3⁄8" hose was used instead. The smaller hose restricted air flow, which created a substantial pressure drop. Furthermore, the 3⁄8" hose used “standard 3⁄8" quick disconnects”, which contributed even more to the high pressure drop. The two standard 3⁄8" quick disconnects, accounted for a combined pressure loss of 23 psig per station, were replaced with larger capacity 3⁄8" quick disconnects at $2.50 extra per set. Doing so reduced the combined pressure loss to only 2 psig per station. The 3⁄8" hose was replaced with an 1" pipe running to the base of the workstation at a cost of $30 per station. A regulator was selected to deliver full flow to the grinders at 75 psig with 80 psig(+) feed pressure. We were then able to reduce the header pressure to a controlled 85 psig. Results after 18 months: p p “In many cases, . too high and too low pressure can cause tool damage and significantly reduce the time between rebuilds.” Tool repair costs went down for the grinders. Production was increased throughout the plant by 30% including installing more grinders and other new equipment. The cost of materials to implement the changes amounted to $1,362. Total operating hp during production fell from 1,500 hp to 1,400 hp with a 30% increase in production. p p www.airbestpractices.com 57 http://www.airbestpractices.com
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