Why/How is there a shift in a Control Valve Characteristic Curve between Inherent and Installed?

[SilverRule]

Can anyone explain how fundamentally the inherent characteristic curve of a control valve shift UP and LEFT when it's installed?

I understand that there's other pressure-generating and pressure-reducing components in the system that affect the curve. But what is the mechanism behind why it shifts UP and LEFT specifically? In other words, whether for characteristic is linear or equal percentage, why can more flow be achieved at a smaller valve opening after the control valve is installed?

I'm going through Crane TP410 and have also looked at other resources but haven't been able to find a clear explanation.

Thanks!

 

[LittleInch]

It's been boggling my brain for the last couple of days but I think i've got it straight.

The issue is the lack of definition about what is meant by installed versus inherent.

What I think this is is that you tend to look at the start and end points of a piping system which includes a control valve.

So because at higher flows your piping system takes a larger proportion of the pressure drop, at lower flows the pressure across the control valve increases as a proportion of the total or increaase to reduce flow if the end pressures are fixed.

Hence at say 50% closed, the effective CV when you look at the ends of the piping system from inlet to outlet increases.

If you just looked at the pressure either side of the valve then the increased DP would be seen.

A lot of the graphs I think swap CV and flow without really saying why or any of the assumptions behind it.

I could be wrong, but that's my take on this.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

Please do not hijack another post. This post will be deleted.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.