Control Valve's Controlbility Range 2

[ghamsa]

Please help on the questions below.

I know that valve's good controllability range is from 20% to 80% opening. Dose this rule apply to all kinds of valves, what about a ball valve??

Are the steps used to design a PCV same as steps for a FCV??


Thanks for your help on this issue

 

[jsummerfield]

A globe valve has good rangeability to 100% travel. The control is less usefull for both butterfly and ball valves as the opening exceeds about 70%. I think that Cv tables increase but more of the pressure drop is recovers at wider openings. You can see this using the Fisher formulas for a specific valve pattern and throw-down numbers trying to calculate valve capacity with all valve details input.

John

 

[saxon]

ghamsa, Pick yourself up a copy of Fisher Controls, "Control Valve Handbook". It will give all the info you need to size for slurry, liquid, vapor, gas service for pressure, temp., flow, and level control.

Hope this helps.
saxon

 

[rmw]

Different types of valves have differing ranges of optimum rangeability.

Even valves within a particular type, say globe type, can have vastly different characteristics, as well as rangeability through the variety of plug styles.

Valves, in order to have controllability have to have some pressure drop associated with them. For that reason, ball valves do not have good controlability at or near 100% opening, while a globe style valve with the right trim and characteristic might have good controlability all the way out to 100%.

Lots of variablility in this topic.

rmw