## Pressure Drop across Butterfly Valve

## Pressure Drop across Butterfly Valve

(OP)

Hello,

I am trying to compute the pressure drop across a 20 inch butterfly valve at various valve positions for throttling a supercritical carbon dioxide stream in a pipe. I found an equation for calculating the pressure drop for compressible fluids across valves in an Emerson manual (the equation is on page 120):

http://www.documentation.emersonprocess.com/groups/public/documents/book/cvh99.pdf

However, I am unsure what value I should use for the expansion factor. I see in the manual it also talks about the critical pressure drop, but I do not know how to determine this point.

I am trying to compute the pressure drop across a 20 inch butterfly valve at various valve positions for throttling a supercritical carbon dioxide stream in a pipe. I found an equation for calculating the pressure drop for compressible fluids across valves in an Emerson manual (the equation is on page 120):

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However, I am unsure what value I should use for the expansion factor. I see in the manual it also talks about the critical pressure drop, but I do not know how to determine this point.

## RE: Pressure Drop across Butterfly Valve

It sounds like your upstream pressure is constant and you wish to know the pressure drop across the valve at different openings. Note that depending on the system hydraulics the downstream pressure will change based on flowrate which will affect valve DP. You need to understand the system hydraulics to know what process conditions the valve will encounter.

## RE: Pressure Drop across Butterfly Valve

To clarify, my upstream pressure and flowrate will not be constant if the valve is being used to throttle. If I cannot use these set of Emerson equations is anyone aware of any other equations that I could apply?

## RE: Pressure Drop across Butterfly Valve