Actuator for a valve

An actuator for a valve in a subsea installation, the valve having a valve element which is movable between a first position and a second position and a spring which biases the valve element toward the first position, the actuator comprising:

• a hydraulic cylinder which includes a movable piston, the piston being mechanically connectable to said valve element;
• a fluid pump which is connected to said hydraulic cylinder through a first hydraulic line, said fluid pump being adapted to supply fluid to the hydraulic cylinder through the first hydraulic line at a sufficient pressure to move the piston and thereby move the valve element to the second position;
• a reservoir for storing a quantity of hydraulic supply fluid at a pressure that is less than said sufficient pressure;
• a second hydraulic line which provides a fluid passage between the first hydraulic line and said reservoir;
• a bypass control unit which is located in said second hydraulic line and which comprises a movable element that operates to open or close said fluid passage;
• first and second force generating means, both of which bias the movable element to a position to close the fluid passage;
• and
• a third force generating means which biases the movable element to a position to open the fluid passage, the third force generating means being configured to operate independently of both the first force generating means and the second force generating means.