Direct Hydraulic Control
Control method wherein hydraulic pressure is applied through an umbilical line to act directly on a subsea valve actuator. NOTE Upon venting of the pressure at the surface, the control fluid is returned through the umbilical to the surface due to the action of the restoring spring in the valve actuator. Subsea functions may be ganged together to reduce the number of umbilical lines.
Source: API SPEC 17F, Specification for Subsea Production Control Systems, Second Edition, December 2006 (Reaffirmed April 2011). Global Standards