If you are working as a mechanical engineer for a valve company which does not have the engineering capabilities in terms of hardware, software and HR, you may need to take a different approach to this.
In almost all cases, the torque to be developed is when the diff pressure across the valve is equal to the larger of the process design pressures on either side of the valve.
There should be common forum from manufacturer engineering, but it's little difference based on diff design and different factor added, so you would better confirm to your suppler.