3 replies to this topic

[medelamine]

Dear all, Hello

 

Can you kindly explain if the pressure drop across an installed valve will change when the operators change the flow through it, or at least the composition of the flow ?

 

If Yes I, is this change predictable ? 

 

I am working on a simulation of an amine plant, where the pressure of rich amine in the absorber outlet must be decreased by 50 bars, before going into regeneration. I would like to change the amine flow or composition, and I wonder if in a real case this will affect the pressure drop across the valve. 

 

Thank you in advance, 

Edited by medelamine, 17 September 2015 - 01:47 AM.

[pavanayi]

Medelamine,

 

The answer to your question should be obvious if you went back to basics and checked the equation for pressure drop across a valve. 

 

Q = Cv*sqrt(ΔP/G)                                  where Q is flowrate, and G is sp. gravity (in consistent units).

 

Now, if the valve opening is not changed when the flow rate is varied, what will happen?

Have you got your answer now?

Edited by pavanayi, 17 September 2015 - 03:07 AM.

[medelamine]

Thank you very much pavanayi, 

 

Indeed, The flow coefficient equation relates the flow to the pressure drop, but I was wondering why it does not include the effect of the valve opening ? can you tell me how this is estimated ?

 

so, we can have the same pressure drop even if the flow changes just by adjusting the valve opening ? 

[latexman]

Basically, the Cv changes with valve opening.  Control valve vendors can supply information specific to their control valves.  There are some general, theoretical relationships - linear trim and equal percentage trim.

 

Usually, as a control valve closes, flow decreases, total pressure drop stays about the same, pipe and fitting pressure drop decreases, and control valve pressure drop increases.