What causes PRV blowdown?

[JoeBobJenkins]

This might be a stupid question but what causes blowdown pressure? Why would the pressure to open the valve be different than resetting the valve, or at least significantly different?

 

[LittleInch]

Basically momemtum of the flowing fluid / force of the fluid against the disc or sealing mechanism.

 

[JoeBobJenkins]

thanks, that was my first thought but then I thought how could that be significantly higher than the base pressure. I guess it is.

 

[Latexman]

Mojojojo69,

Take a deep dive into the “huddling chamber” of a PSV. Use AI, and there are some YouTube videos out there. Any questions, come back here.

 

[LittleInch]

That's the art of the design. Once you start to flow you want the valve to open fully with a very small increase in pressure. There's a lot of effort goes into the design.

Blowdown percent is normally in the range 7 to 10%. So difference in force is not that big.