Motor-operated valve functions to block or connect the flow of fluid in nuclear power plant and especially safety-related valves are evaluated with operability margin calculations, that should have positive value in both open and close stroke. Although all actuators have inertia force which increase operating margin of valve closing stroke, inertia force, after control switch operation in actuator is not considered in evaluating operability margin calculation process. In this paper, the hidden margin by inertia force of each actuator model in closing stroke was studied quantitatively.

A valve open/close degree measuring device is used for an indicator of a valve actuator. This device indicates an opening and closing of a valve or throttle in a hydraulic actuator. In ship, equipments requires safe and robust because of a rough environment and a specific condition during a voyage. Thus, the open/close degree measuring device must be developed which can be used at an outdoor environment. This study developed the open/close degree measuring device using a volumetric measuring method(25㎖/100㎖). The housing of the open/close degree measuring device was made by a stainless steel with surface painting after an anodizing coating.