Actuator maximum shutoff delta pressure is the maximum differential pressure (between inlet & outlet) that the actuator still could hold out the close position. Normally control valve shall not be used as a shutoff valve (shutdown valve). The one who act as a shutoff valve usually is an actuated ball valve. Therefore the maximum shutoff pressure for control valve may have different value with the one from shutdown valve. But if the value is the same it’s more good or preferable.
For simplicity we could specify maximum shutoff delta pressure as the design pressure. For example, if we have a valve with 600 Class and the design pressure is 800 psig, then we could specify that the maximum delta pressure is 800 psig.
Another way to determine the maximum shutoff delta pressure is the PSV (Pressure relief/safety valve) setting.