Control valve Cv selection

[kajang]

salam,

Referring to PTS 32.36.01.17 rev December 2008, Appendix 2 Cl 2.2, valve opening at max flow rate shall be max 80% and should not be less than 30% opening at min flow rate. One clarify to me that this range is a good control range, if we go below or higher than this figure, control is not in good range. Anyway, other than control performance, do we have any problem if valve opened less than 30%?

Secondly, if say we need to comply with this requirement, will follwing help and normally done:
1) 2 parallel valve, split range application.
2) use of rotarytype style.
3) use multi stage trim valve (normally used for severe application.

Thanks in advance.

[azhar]

Waalaikummussalam.

Belum dapat latest PTS standard ni.

Yes 30 to 80 is good engineering practice. This usually can be meet . But in some cases you will find that you need to operate slightly beyond the range say at 15% for short duration of time. You will need to make good engineering judgment whether to install another valve which normally will be closed all time or select valve that can operate at small opening.

What is the problem if valve open less than 30% ?. At small opening, there is potential high velocity that will cause erosion to the trims.

Hope this helps.

Wallahuaklam