I have two orifices ( Capillary type ) in series in H2 service at 30 kg/cm2_g and 40 Deg C. Line size is 0.75 inch. As per their datasheet
1st Orifice: Do = 0.51 mm & L = 50 mm ; Pressure drop at Max flow : 6.89 kg/cm2_g
2nd orifice: Do = 0.51 mm & L = 50.83 mm ; ; Pressure drop at Max flow ...