Why does the gas-over-oil actuator sizing require the valve torque figures at both minimum and maximum supply pressure in the pipeline?

Gas-over- oil actuators use the pressure gas flowing through the valve as the fluid motive power for the actuator itself. The pressure conditions in the pipe are not only affecting the valve torques, but also the working conditions of the actuator.
Since such pressure is delivered unregulated to the actuator and control system, the latter must be suitable for any pressure condition present in the pipe. The actuator sizing based on the valve torque figures at the extreme values of minimum and maximum pressure makes sure the actuator can properly stroke the valve in any intermediate condition within the min and max pressure ones.