This automation industry quiz question comes from the ISA Certified Automation Professional (CAP) certification program. ISA CAP certification provides a non-biased, third-party, objective assessment and confirmation of an automation professional's skills. The CAP exam is focused on direction, definition, design, development/application, deployment, documentation, and support of systems, software, and equipment used in control systems, manufacturing information systems, systems integration, and operational consulting. Click this link for more information about the CAP program.
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?
a) globe
b) butterfly
c) ball
d) eccentric plug
e) none of the above
Click Here to Reveal the Answer
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)]
Where,
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.
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