How to calculate control valve diameter size ,let’s give you some brief introduction about how to confirm whether the diameter is suitable for the control valve.
Control valve working condition：Medium:Liquid nitrogen，t=33℃，λ=5.9×10^-4kgf/cm3,Pv=15×100kPa,Qmax=15m3/h,the corresponding Qmax p1,p2,△pmin is （530、130、400）×100kPa，Qmin=5m3/h,△pmax = 500×100kPa,s=0.2, choose high pressure control valve ,flow characteristics:linear ,with positioner,what diameter(DN) is suitable for the control valve?
1.Flow capacity：Qmax=15m3/h。
2.Pressure difference：△pmin = 400×100kPa,△Pmax=500×100kPa.
3.Kv value calculation:
Step 1：we can know from datasheet :Fl=0.8.
Step 2：flow state:0.5p1＞＞pv,Therefore:
And △pmin > △pc,so it is block flow.
Step 3：Adopt the KV value calculating formula of block flow state
4.According to Kvmax=0.64，Check the flow coefficient of the high pressure control valve，get DN=10，dg=7,and Kv=1.0
5.The opening of calculation
Because Kv=1,the control valve only has linear flow characteristic，adopts linear culculating formula.
The max. opening Kmax＜89%，The min. openingKmin＞10%，so Kv=1.0 is qualified.
6.Adjustable ratio calculation.
The calculation result is qualified.
7. the pressure different calculation △p＜[△p],（because ds＜dg）is qualified.
8.Conclusion：DN=10，dg=7，Kv=1.0, Calculation is qualified.
