Mechanically locked actuator system and method

A spring force assembly, comprising:

• a sleeve configured to move axially along a valve axis responsive to movement of a valve stem;
• a collet positioned circumferentially about the sleeve and configured to receive a force from the sleeve at a shoulder interface between the collet and the sleeve, wherein the collet is configured to flex responsive to movement of the sleeve past a predetermined position;
• a spring positioned radially outward from the sleeve and configured to move from an extended position to a compressed position responsive to movement of the collet;
• and
• a groove associated with a valve actuator to receive an expanding profile of the collet when the expanding profile is aligned with the groove, the expanding profile configured to be driven radially outward and into the groove by the sleeve.

A method, comprising:

• determining a desired spring closing force;
• determining an actuator spring closing force of an actuator spring to be used with an actuator for a valve assembly;
• determining a spring force assembly closing force based, at least in part, on a difference between the desired spring closing force and the actuator spring closing force and a shear force for a component associated with the valve assembly;
• and
• positioning a number of spring assemblies within an actuator housing, wherein each spring assembly has an associated spring assembly closing force less than the spring force assembly closing force.