$$
d_{orifice}  = \root 4 \of {{{\left( {1 - {{Q_s^2 } \over {Q_l^2 }}} \right) \cdot D_{pipe} ^4 } \over {\left( {\left( {\sum K  + f{{L_l } \over {D_{pipe} }}} \right) \cdot {{Q_L^2 } \over {Q_s^2 }} - \sum K  - f{{L_s } \over {D_{pipe} }}} \right) \cdot K_{orifice}^2  \cdot n_{orifice}^2 }}} 
$$