Compressed Air Best Practices - October 2008 - (Page 55) Compressed Air Industry AUTOMOTIVE TRANSIT | 10/08 | 1 ⁄2 – 3⁄4 HP CLASS 3 1–1.5 HP CLASS 2–3 HP CLASS INLET AIR PRESSURE 1 ⁄2 HP .35 20 .41 21 .5 22 .57 24 .65 26 ⁄4 HP .47 1 HP .765 27.5 .95 32 1.13 36.5 1.4 39 1.5 45 1.5 HP .927 30 1.15 35 1.38 40 1.5 42 1.82 50 2 HP 1.74 51 2.16 59.6 2.58 68 .30 76.5 3.42 85 3 HP 2.32 67 2.88 78 3.44 89 4.0 100 4.56 111 Maximum HP 60 psig Scfm at maximum HP Maximum HP 70 psig Scfm at maximum HP Maximum HP 80 psig Scfm at maximum HP Maximum HP 90 psig Scfm at maximum HP Maximum HP 100 psig Scfm at maximum HP 20.1 .58 53.4 .69 26.7 .8 30 .91 33 Performance Parameters p Summary p Most air tools manufactured for North American use are designed not to run over 100 psig inlet pressure unless specifically stated The average tool is designed for optimum performance between 80 and 90 psig inlet pressures. At 70 psig, most will still operate, but below rating. At 60 psig, the performance is seriously affected and will probably be unacceptable. Below 60 psig is not really considered a viable option. The approximate losses at various inlet pressures in the 1 hp to 3 hp class air motors are: 100 psig to 90 psig — 7% to 17% 90 psig to 80 psig — 7% to 16% 80 psig to 70 psig — 17%(+) 70 psig to 60 psig — 20% 100 psig to 60 psig — 50% 90 psig to 60 psig — 39% 80 psig to 60 psig — 33% p Inadequate compressed air supply will result in drops in power and probable losses in rpm. Both of these will have a very significant impact on productivity. Air supply to a process and/or tool operation, should be made knowing the total full operational flow and the length of hose to be used along with the minimum effective inlet pressure. Do not use connection size as a guide! p Hose selection For example: the most common hose sizes for plant use are 3⁄8" to 3⁄4" with 300 psig working pressure. The selection of air hose size is often left to the operator from a choice of 3⁄8", 1⁄2" or 3⁄4" and 1" hose. The operator often selects the 3⁄8" hose regardless of tool used because: p ⁄8" hose appears to be the lighter and “easiest to handle.” 3⁄8" hose is not generally recommended for industrial or automotive applications. 3 www.airbestpractices.com 55 http://www.airbestpractices.com
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