Applied Product Catalog 2016 2017 Page i41 Technical Reference

Valves All Things Industrial SM i41 Most manufacturers' catalogs provide flow ratings for valves in Cv, based on National Fluid Power Association (NFPA) standard T3.21.3. The following tables and formulas will enable you to quickly size a valve properly. The traditional, often-used approach of using the valve size equivalent to the port in the cylinder can be very costly. Cylinder speed, not port size, should be the determining factor. The following Cv calculations are based upon simplified for- mulas which yield results with acceptable accuracy under the following standard condition: Air at a temperature of 68 F (20 C) Absolute downstream or secondary pressure must be 53% of absolute inlet or primary pressure or greater. Below 53%, the air velocity may become sonic and the Cv formula does not apply. Nomenclature: B Pressure drop factor C Compression factor Cv Flow factor D Cylinder Diameter (I N) F Cylinder Area (SQ IN) L Cylinder Stroke (I N) p1 Inlet or Primary Pressure (PS I G) p2 Outlet or Secondary Pressure (PS I G) p Pressure differential (p1- p2) (psiD) q Air flow at actual condition (CFM) Q Air flow of free air (SCFM) t Time to complete one cylinder stroke (SEC) T Absolute temperature at operating (R) pressure. Deg R = Deg F + 460 Valve Sizing for Cylinder Actuation Direct Formula Example: Cylinder size 4" Dia. x 10" stroke. Time to extend: 2 seconds. Inlet pressure 90 psiG. Allowable pressure drop 5 psiD. Determine Cv. Solution: F = 12.57 Sq. In. (Table 1) C = 7.1 (Table 2) B = 21.6 Select a valve that has a Cv factor of .7 or higher. In most cases, a 1/4" valve would be sufficient. It is considered good engineering practice to limit the pressure drop Dp to approximately 10% of primary pressure P1. The smaller the allowable pressure drop, the larger the required valve will become. After the minimum required Cv has been calculated, the proper size valve can be selected from the catalog. Table 1: Table 2: How to Determine Proper Air Valve Size Cv= 12.57 X 10 X 7.1 = 0.7 21.6 X 2 X 28.8 Cylinder push bore area F for standard size cylinders Bore Size D (In.) Cylinder Area F (Sq. In) Bore Size D (In.) Cylinder Area F (Sq. In) 3/4 0.44 4 12.57 1 0.79 4 1/2 15.90 1 1/8 0.99 5 19.64 1 1/4 1.23 6 28.27 1 1/2 1.77 7 38.48 1 3/4 2.41 8 50.27 2 3.14 10 78.54 2 1/2 4.91 12 113.10 3 1/4 8.30 14 153.94 Cv = Cylinder Area (F) (Sq. In.) (See Table 1) X Cylinder Stroke (L) (In.) X Compression (C) Factor (See Table 2) Pressure Drop (B) Factor (See Table 2) X Time to Complete Cylinder Stroke (Sec) X 28.8 Compression factor C and pressure drop factor B Inlet Pressure (psiG) Compr. Factor C Pressure Drop Factor B for Various Pressure Drops p 2 psiD 5 psiD 10 psiD 15 psiD 20 psiD 10 1.7 6.5 - 20 2.4 7.8 11.8 - 30 3.0 8.9 13.6 18.0 - 40 3.7 9.9 15.3 20.5 23.6 - 50 4.4 10.8 16.7 22.6 26.4 29.0 60 5.1 11.7 18.1 24.6 29 32.0 70 5.8 12.5 19.3 26.5 31.3 34.8 80 6.4 13.2 20.5 28.2 33.5 37.4 90 7.1 13.9 21.6 29.8 35.5 39.9 100 7.8 14.5 22.7 31.3 37.4 42.1 110 8.5 15.2 23.7 32.8 39.3 44.3 120 9.2 15.8 24.7 34.2 41.0 46.4 130 9.8 16.4 25.6 35.5 42.7 48.4 140 10.5 16.9 26.5 36.8 44.3 50.3 150 11.2 17.5 27.4 38.1 45.9 52.1 160 11.9 18.0 28.2 39.3 47.4 53.9 170 12.6 18.5 29.0 40.5 48.9 55.6 180 13.2 19.0 29.8 41.6 50.3 57.2 190 13.9 19.5 30.6 42.7 51.7 58.9 200 14.6 20.0 31.4 43.8 53.0 60.4 210 15.3 20.4 32.1 44.9 54.3 62.0 220 16.0 20.9 32.8 45.9 55.6 63.5 230 16.7 21.3 33.5 46.9 56.8 64.9 240 17.3 21.8 34.2 47.9 58.1 66.3 250 18.0 22.2 34.9 48.9 59.3 67.7

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