The Petro Controls “HCTH2C” interface is a 2-way, normally open, pilot operated, automatic hydraulic controller with manual override. It is normally installed in a SCSSV or SSV control panel. During normal operation, instrument pressure holds the controller in closed position. The supply pressure is blocked and the hydraulic system will maintain it’s required working pressure. When the instrument pressure is bleed off, the valve will vent the supply pressure to return.