3 replies to this topic

[marcoz1121]

Hi fellow forumers,

 

Currently I am doing a control valve simulation on HYSYS. I have the valve datasheet that already specified the parameters including flow, valve opening, valve CV etc.

 

I am trying to mimic the datasheet (which i know that i cant because the valve manufacturer may use their own software on sizing the valve). However, I tried to simulate the valve, and I found that at given flowrate and delta P, when I increased the valve opening, the Cv actually decreased. I thought that increasing the valve opening will lead to increasing Cv.

 

Hope I can get some insight on this. Thank you

[latexman]

It’s not perfectly clear to me exactly what you did. Was flow rate constant for all CV openings? Was dP constant for all CV openings? The way I interpret what you said, both flow rate and dP were constant for all valve openings. That sounds over-specified to me.  Can you provide more details please?

[Fletch]

Increasing the valve opening will increase the available Cv of the control valve, other system effects (e.g. increased flow or lower pressure drop) will change to match the Cv of the valve.

 

One thought to what you were seeing "increased valve opening, lower Cv" is if you are using the Rating view in HYSYS and use SIZE VALVE.

The tool gives you the full open Cv value for your conditions.

 

Say you size the valve at the flow conditions at say 50% open and get a Cv of 40.

You then change only the % open to 100% and size the valve, you will get a Cv of 20.

 

Your conditions haven't changed except the %open, but you have asked the program to SIZE the valve, the size of the valve is defined at the full open condition.

The % open can be used to determine to understand how open the valve will be for your changed conditions, when you know the full open Cv. You adjust the % open until your Cv matches your figure.

 

As mentioned at the start, to see the increased Cv for the %open, you need to change the main inputs (increase flow or lower dP)

Edited by Fletch, 28 July 2024 - 07:09 AM.

[Dacs]

Are you doing this in steady state?