Cv blowdown valve

[justitia]

Hello everyone

I have to calculate the required Cv for a blowdown valve.
The fluid is boiler feed water. I know the mass flow, pressure and temperature input and output, corresponding to saturated steam (eg 50 bar, 263 ° C).
What formula should I use? Liquid or dry saturated steam?

Thanks

 

[gerhardl]

Hello justitia,

..this is a 'technical art' more than a pure cv-calculation.

More than one blow-down valve and differing placements could be necessary, depending on the vessel type and construction, and worst-case considerations (a certain amount of liquid fluid within a certain time is always integrated) have to be taken into account, on top of somewhat differing regulations around the world....

Best would be to contact a well renowned supplier of blow-down valves, for instance Gestra - Flowserve, which have calculation programs where you put in the different parameters, and they could also proably advice through nearest technical department.

Do not forget that the resulting steam from the blowdown has to go somewhere, and expand and deenergize without creating damage on pipelines, expanding tanks or people....

Check for instance below link or other suppliers:

http://www.flowserve.com/files/Files/Literature/ProductLiterature/FlowControl/Gestra/818424.pdf

 

[justitia]

Thanks gerhardl,

so I can rely on the tables of manufacturers according to the scale and pressure of the boiler indicates the orifice? But no account of the pressure drop ..

Thanks

 

[gerhardl]

My advice is to be sure to check valve dimension and function by presenting all technical details including vessel construction, piping details and fluid details and not focus on the blowdown valve as a 'freestanding' item alone.

The best suppliers can supply extra information on development, regulations, equipment and automation possibillities for vessel control.

(Ask two different suppliers/brands and compare!?)

Good luck!