摘要：Hydraulic systems provide a clean and stable supply of hydraulic fluid for subsea valves and actuators installed on the subsea bed in subsea production *** control systems are used for contemporary subsea fields instead of installing the control system on *** all-electric subsea systems are state-of-the-art with benefits such as health,safety,and environment improvement,as well as efficiency and lower cost,hydraulic systems are still used for the development of many subsea *** of the main questions in the selection of a subsea hydraulic field is whether to choose an open or closed loop hydraulic *** main characteristic of an open loop hydraulic system is that the hydraulic fluid is discharged into the marine environment during the actuation of the subsea ***,the hydraulic fluid is returned to the topside facilities through an umbilical system in a closed loop *** that closed loop systems are more eco-friendly,the main question in this research is to examine the effect of the actuator connection of the closed loop system on actuator *** cases of actuated valves connected to a closed loop system are analyzed in this *** first is a 71/*** slab gate valve in the pressure class of 517 bar with a linear spring return fail-safe close(FSC)actuator located on a manifold *** data indicates that the piston rod and cylinder diameter of the FSC linear actuator should be increased by some millimeters due to the accumulation of hydraulic oil at the bottom of the *** hydraulic oil in the closed loop system helps in closing the actuator and spring force,so the spring constant and torque should be reduced as a *** second case involves a *** ball valve in the pressure class of 517 bar with a double-acting fail-as-is rack and pinion *** conclusion in this case is to avoid making any change in the design of double-acting actuator in connection to the closed loop sy