What is equal percentage characteristic of control valve? which valve is used for what application?

 

I have spoken about this before under the boiler drum level subject. You are asking a question covering a wide range of answers.

Briefly I chose an equal percentage valve when the inlet pressure is falling as the valve opens. (Drum level control with a falling feed pump pressure as the valve opens) The opening in the trim is very similar to a V notch such that as the valve opens it will alow a greater flow increase.

Go to the Fisher Control Valve site and download a free copy of their control valve book. It is an excellent reference manual with very little vendor promotion. Have a look at page 109. very good graphic that explains it at a glance.

If the inlet pressure remains contant throughout the valve travel it can create some interesting tuning problems. In that situation use a linear trim.