12_Control_Valves_Chap9S10_4

15 b calculate the valves rated cv the value that

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Unformatted text preview: fluid through equipment increases, but pressure available from pump often decreases ! 14 15 How would you calculate the numbers for these curves ? For case (a) linear valve, q is NOT linear with lift ! c) Compute q as a function of using Eq. 9-2, the rated Cv, and ΔPv from (a). A plot of the valve characteristic (q vs. ) sho should be “reasonably” linear in the operating region of be “reasonabl linear in the operating region interest (at least around the design flow rate). If it is not suitably linear, adjust the rated Cv and repeat. Example 9.2 – pg. 219 SEM2 A pump furnishes a constant head of 40 psi over the entire flow rate range of interest The heat exchanger pressure drop 30 psig rate range of interest. The heat exchanger pressure drop is 30 psig at 200 gal/min (qd) and can be assumed to be proportional to q 2. Select the rated Cv of the valve and plot the installed characteristic for the following case: a) A linear valve that is half open (l = 0.5) at the design flow rate. 16 Chapter 9 Chapter 9 b) Calculate the valve’s rated Cv, the value that yields at least 100% of qd with the available pressure drop at that higher flow rate. Figure 9.12 Installed valve characteristics for Example 9.2. 17 Solution This should be Chapter 9 Chapter 9 First we write an expression for the pressure drop across the heat exchanger (assumes pressure drop is proportional to squ...
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