hi sir the question is: in desiging process, we should select proper size of valves. in calculation process, we don’t have any information about pressure in down or upstream of flow. so how can we determine the P1 and P2 ?
In almost every industries there will be need for a valve with specific Cv and/or pr inlet and pr outlet Or we can calculate dynamic pr from inlet velocity
In general, control valve will be sized and selected by its manufacturer.. Their sizing sheet will include Cv. We can cross verify our calculated Cv with Manufacturer's selected Cv.
Flashing happens due to pressure drop in valve which converts liquid to vapour Meanwhile cavitation occurs due to pressure drop in valve which converts liquid to vapour and back to liquid again
