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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. )
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
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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- Winter '08