Restriction Orifice calculation

You can use formulas in Crane or any other good hydraulics textbook.
We have an in-house program which gives for 30 m3/h water at 15 C and for 5 bar pressure loss an orifice hole size of 23 mm.
Regards,

Joerd

Utlaan
Joerd's recommendation of the Crane "Flow of Fluids" Publication (No.410) is sound. You can get it from I caution that you need to clear up your pressure statement. I guess that the 5 bar (gauge pressure? barg ?) is upstream pressure but the orifice will be sized on the pressure loss across the orifice so, unless you are discharging directly to the atmosphere, you will need to calculate the down-stream pressure losses which create a back pressure on the orifice. The Crane book helps there also.

I use my in-house program with the following input:
ID pipe: 78.1 mm ( 3" STD)
Full scale : 36 M3/hr
Normal : 30 m3/hr
Temp.: 15 oC
Normal Pressure: 5 Kg/cm2g
density : 998 kg/m3
viscocity: 1 cp

and gives the result:
Max Reynold: 162700
Norm. Rey. :135600
Dia meter Ratio : 0.5720
Flow Coef: 0.6435
Exp. fac : 1
orifice Diameter: 44.7 mm
Max Press. Loss : 3260.5 mmH2O
flow range : 34.3 - 100%

Reference: JIS Z8762-1969 Orifice Sizing.
Unfortunetly I don't have JIS standard for checking.