12_Control_Valves_Chap9S10_4

8 control valve characteristics f is the flow

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Unformatted text preview: is valid for nonflashing fluids (single phase). Figure 9.8 Control valve characteristics. −1 f is the flow characteristic, not flow rate = q ! 12 13 where R is a valve design parameter that is usually in the range of 20 to 50. The rangeability of a control valve is defined as the ratio of maximum to minimum input signal level. For control valves, rangeability translates to the need to operate the valve within the range 0.05 ≤ f ≤ 0.95 or a rangeability of 0.95/0.05 = 19. Control valves are normally not operated to cut off flow completely! To “Design” / Select an Equal Percentage Valve: a) Plot the pump characteristic curve and ΔPs , the system pressure drop curve without pressure drop curve without the valve, as shown in Fig. 9.10. valve, as shown in Fig. 9.10. The difference between these two curves is ΔPv . The pump should be sized to obtain the desired ratio of ΔPv / ΔPs , for example, a ratio of 0.25 – 0.33 = the pressure drop across the valve is 25 to 33% of the drop across the equipment, at the design flow rate qd. Chapter 9 Chapter 9 Rangeability Figure 9.10 Calculation of the valve pressure drop ( ΔPv ) from the pump characteristic curve and the system pressure drop without the valve ( ΔPs ) .As flow increases, pressure required to force...
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This note was uploaded on 04/17/2010 for the course CHE 461 taught by Professor Staff during the Winter '08 term at Oregon State.

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