126 www.stauff.com/6/en/#126 G Determination of the Nominal Diameter Using a Nomogram This nomogramm provides a guide for the determination of the nominal diameter (DN). We recommend to use the following flow rates as a basic guideline: Suction lines: 0,5 ... 0,8 m/sec (.15 ... .24 ft/sec) Return lines: 2,0 ... 4,0 m/sec (.61 ... 1.22 ft/sec) Pressure lines >10 MPa: 2,0 ... 4,0 m/sec (.61 ... 1.22 ft/sec) Pressure lines >50 MPa: 3,0 ... 12,0 m/sec (.91 ... 3.66 ft/sec) Example 1 Velocity v = 8 m/sec (2.44 ft/sec) Flow rate Q = 150 l/min (40 US GPM) The straight line linking these two values on the outer scales intersects the nominal diameter DN 20 on the middle scale. Example 2 Velocity v = 5,5 m/sec (1.68 ft/sec) Flow rate Q = 66 l/min (17 US GPM) The straight line linking these two values on the outer scales intersects the nominal diameter DN 16 on the middle scale. Please note: No allowance is incorporated for the resistance of the pipes, elbows and valves, viscosity, the effect to temperature on viscosity and other factors. Contact STAUFF for further information. Determination of the Nominal Diameter Using a List of Nominal Flow Rates The indicated flow rates have been determined for ball valves in open position with water at a temperature of +15°C / +60°F. KvCoefficient The nominal flow rate coefficient Kv according to German standard VDI/VDE 2173 indicates the quantity of water in cubic meter per hour (m³/h) at ∆p = 1 bar / 14.5 PSI and 35 mm²/s (cSt) at +5 ... +30°C / +41 ... +86°F. CvCoefficient The Cv value (which is still common practice in USA) specifies how much US gallons of water flow through the valve per minute (US GPM) at ∆p = 1 bar / 14.5 PSI at +15°C / +60°F. Contact STAUFF for further information. Nominal Size DN Kv Cv (mm) (in) (m3 /h) (US GPM) 15 1/2 19,4 22,6 20 3/4 45,6 53,0 25 1 71,5 83,1 32 1-1/4 105 122,1 40 1-1/2 170 197,7 50 2 275 319,8 65 2-1/2 507 589,5 80 3 905 1052,3 100 4 1414 1644,2 125 5 2362 2746,5 150 6 3694 4295,3 Example 2 Example 1 Catalogue 6 § Edition 06/2024 Technical Appendix
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