I had two questions regarding pressure drop in valves, hopefully quite easy for you guys.1. I'm performing a pressure drop calculation on various pipes, still in early design stage. Valve types are specified but no exact models, so I can't ask the manufacturer for Kv-values. I have used some "typical" Kv-values for the valves from some specific manufacturers, but the customer does not like this. Is there some norm that would supply Kv/zeta values per valve type/size that i could refer to instead? My old school books did not impress either.2. I have a problem with possibly too high pressure drops in a system and asked the valve supplier what the pressure drop in his valve would be at the wanted flow. I got the answer that:dP = rho * (Qs / Kv)^2dP = Pressure drop [bar]rho = Density [kg/dm3]Qs = Flow [m3/h]If the valves are control valves, there is another dimension in the consideration. a 4" (100mm) valve may have a Cv of 200(Kv 168), but that's only in the fully open case. Control valves are not ever supposed to be fully open, and typically operate at around half-stroke or 20% of capacity,(cv~40, Kv=~33) making a LOT more pressure drop than the unrestrictive isolation valves installed next to them. Viscosity. It's a funny thing. There is very little effect from viscosity as long as the flow is turbulent. Then the standard Cv(Kv) equation works well. As pointed out earlier, syrup and water have different densities which are reflected in the Cv (Kv) calculation and account for the variation in results. At low Re (<40,000) the viscous effects become significant. In the laminar flow region there is a different equation to describe the relationship between the variables. Checking and correcting for viscous flow is tedious. Computerized sizing programs automatically evaluate and correct for viscous effects.

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