When it comes to ESDVs and BDVs, I could point out another issue related to actuators: the uncertainty in finding the right torque to drive the valve to its safe condition. This difficulty is usual, I believe, because most of the valves supplied in the market must be hand-operated type valves, so vendors probably do not pay much attention to how accurate their published torques are for their valves. Consequently, we often end up specifying the wrong actuator which, if too small, the valve will not go to its safe condition and, if too big, in addition to a higher cost we may go near (or above which is worst) to the stem maximum allowable torque.
I also found that some valves that stay open for a while (I am not talking about years but only 24 hs) may increase their torques by 20 % or so.
In my company we specify the actuators to have 1.5 times the maximum torque the valve exhibits at any point, which it is generally in the closed to open condition, with maximum pressure at both sides, and cavity to the atmosphere (this is in line to what API 6D requires for torque measurement).
Despite all these precautions, I feel that the valve may get stuck at any time. Does anyone share these concerns? or, has a method to accurately size the actuator?