Control Valves for pH Control

[OilBoiler]

Hi,

I would like to know what type of control valve you would recommend for pH control? Equal percentage, linear, or quick opening?

I understand that equal percentage valves are the most common and provide good control for low flows. But, for my system, I wanted to add small amount of chemicals until a pH between 6 and 9 is reached. I have enough residence time in my basin to be able to do this. That's why I don't know whether I may be able to achieve this with an equal percentage or just use a quick opening?

Thanks!

 

[ilan7]

Usually, when adding chimicals to a large amount of water (like cooling tower), you add the chimicals for few hours and then stop for few hours. In this case an ON/OFF valve will do the jobe as well.
For other control system - usually we prefer the flow change through the valve to be equel to the contro out put signal, and then the equal precentage is used. In other cases (usually pressure control) I would use linear valve positioner. I never had the chance to choose Quick - Openning valve caracteristic (for control).
My recommandation :
1. Use On Off for low chimicals flow,
2. Use Equal precentage or linear valve.

 

[hacksaw]

There are special pH dosing valves with the necessary turndown. You can also use split ranged valving.