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The prime requirements of this valves are tight shut off when closed and minimum restriction to flow when open. The flow resistance will be smaller per lesser existing of abrupt changes in flow direction and cross-sectional area and per lesser raising edges, which could be result in stalling and swirling. The drag coefficient ζ multiplied with the kinetic energy at the valve inlet determines the pressure loss of a valve.
For some known design types the flow during the valve opening process is here displayed, approximately two-dimensional. The images have been calculated with a Navier-Stokes solver, for: valve nominal diameter 50 mm / k,ε-turbulence model / water with 20 C and 5 bars. They show the stream function Ψ colour-coded as well as selective streamlines and are arranged towards of decreasing drag coefficients. The ζ-values are valid for valves with a nominal diameter of 50 mm and full opening, they are taken from H.Sigloch [Technische Fluidmechanik].
By click on the button the appropriate valve opening process will be started;
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