The Main Steam Isolation Valve (MSIV) is crucial safety devices in PWR and BWR NPPS. The Nitrogen-Hydraulic actuator is a popular choice among customers due to its impressive output thrust. However, its complex structure and the working medium utilizes pose challenges for reliability management. One of the most prevalent issues is maintaining stable hydraulic circuit pressure. To address these concerns, a comprehensive review of industry literature and product information was conducted. Additionally, maintenance databases were examined to pinpoint specific problems and commonly encountered failure mechanisms, and discuss proposed modifications aimed at enhancing the reliability of MSIV actuators, in particular, tests were conducted on the pressure relief valve and flow orifice plate to measure the replenishment efficiency of the hydraulic pump under fault conditions. Furthermore, it offers inspection and monitoring techniques that can be implemented as part of a preventive maintenance program.