Hi Have a look at this formula: Cv=((39.693*D^4)/K)^0.5 It correlates Discharge Coefficient (Cv) for a valve with Headloss coefficient (K) of the valve. Please explain this formula and let me know: 1- Is K fixed for a valve in every situations of it? 2- Assume an area of a valve is changed during the time. Which are Cv, K or D fixed and which are changed? 3- Is K fixed during valve's area changing? Thank.