As a Such to my Exp, there is no philosophy for Shut Down Valves to include using Reducers ,

SDV's are basically for ISOLATION of the PLant under Critical or Abnormal situations . SO U put REDUCERS, WHat not, just see whether you are ISOLATING the line pressure < Design Pressure of the Downstream with Simulation of PIPESIM/ PIPENET .

SDV has only two modes , ON/OFF , so depending on the Signal ur Valve Solenoid makes the contact NC/NO to stop the FLOW.