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A globe valve has a pressure recovery factor of 0.83; a butterfly valve has a pressure recovery of 0.61; a ball valve has a pressure recovery factor of 0.63; and an eccentric plug valve a pressure recovery factor of 0.79. Which valve will have the least overall pressure drop?
d) eccentric plug
e) none of the above
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Pressure recovery factor can be defined as “the increase in fluid static pressure that occurs as fluid moves through a valve from the vena contracta to the valve’s outlet and downstream piping.” [ISA-RP75.23-1995]
Mathematically, pressure recovery factor can be expressed as: Cf = FL = √[(P1-P2) / (P1-Pvc)]
P1 = Upstream Pressure
P2 = Downstream Pressure
Pvc = Pressure, vena contracta
The pressure recovery factor is proportional to the square root of the overall pressure drop (P1-P2), so that the valve with the lowest recovery factor will have the lowest over pressure drop.
The correct answer is B, butterfly.