A
subsea actuator and method is disclosed that includes a removable monolithic cap / hydraulic chamber that seals the
actuator housing top with seals placed around the monolithic cap, defines a straight hydraulic line and port for
control line hydraulic fluid, and provides for fasteners to secure the top of the
subsea actuator. The monolithic cap / hydraulic chamber is so limited in
metal and
machine time that it can be a throw-away maintenance item. A preferably cup-shaped spring lifter is provided in telescoping relationship to the hydraulic chamber. Several short
hydraulic fluid passageways are provided in the bottom cup portion of the spring lifter to permit assist
hydraulic control fluid into the hydraulic chamber below the
piston. The driving stem provides a removable connection to the hydraulic
piston from the top of the actuator housing and a quick disconnect permits disconnection of the driving stem from the
valve stem. The
high tension spring does not need to be removed to perform maintenance, and all wear items and seals are readily accessible. Change or replacement of the stem packing is made from the top of the bonnet to avoid dissasembling the bonnet to valve body connection. The spring chamber within the actuator housing may be increased in size to accommodate a larger spring as necessary for fail-
safe operation without changing the size of the hydraulic chamber. All sliding components ride on wear rings to increase the lifetime of reliable
subsea operation. The moving components are mounted in a compact, concentric configuration.