4 replies to this topic

[Lyne]

Hi,

 

How to set the pressure drop for the control valve at a pump discharge? I have different regimes and the control valve is at the booster pump outlet. is there a special requirements for such control vales ?

 

Thank you  

[snickster]

Here is typical sizing criteria for good controlability:

 

Minimum Cv Capacity (Cv Required)

The selected control valve trim capacity (Cv selected) shall meet the

following:

1) An equal percentage trim shall operate below 93% travel at

maximum flow condition. If no maximum flow condition is

specified on the ISS, then the trim shall operate below 85% travel

at normal flow condition.

2) A linear trim and quick opening trim shall operate below 90%

travel at maximum flow condition. If no maximum flow condition

is specified on the ISS, then the trim shall operate below 75%

travel at normal flow condition. Anti-surge control valves shall

operate below 55% travel at maximum flow condition.

3) A modified parabolic trim shall operate below 90% travel at

maximum flow condition. If no maximum flow condition is

specified on the ISS, then the trim shall operate below 80% travel

at normal flow condition.

Commentary Note:

The specified percentage (%) travel positions are for sliding stem type

valves and need to be converted to degrees opening for rotary type

control valves.

Edited by snickster, 04 June 2024 - 02:29 PM.

[breizh]

Hi ,

To add to Snickster's reply, a paper and an excel sheet I prepared years ago.

Breizh

Attached Files

•  Control Valves Match Trim to your Selection.pdf   1.11MB   117 downloads
•  Control valves (match the trim to the selection).xlsx   53.46KB   89 downloads

[walidd_23]

Hello 

First of  all you need to determine the worst case which corresponding the maximum calculated Cv considering the following:

1. Min pressure drop of control valve 0.5 -0.7 bar
2. Max Operating pressure at receiving vessel or destination (HPA)
3. Max liquid level at receiving vessel 
4. Rated Flowrate 
5. Min liquid level at supply vessel

With this condition you will determine the max flow valve condition and rated head of the pumps. 

 

After that you  can do the calculation for normal flow with normal operating pressure and level, and min flowrate to determine the full operating of the control valve.

 

For better estimation it is good to have pump curves  for normal and min case , I have attached and example for the valve hydraulic calculation of this 3 cases using Flowmax

 

 Valve Sizing Cases .pdf   397.38KB   92 downloads

 

Regards 

 

 

Edited by walidd_23, 10 June 2024 - 04:53 AM.

[billjones66]

Here are some free control valve sizing worksheets in excel available for download: https://www.industry...alve_sizing.php