Line Pressure Operated (LPO) Actuator Control System
A Surface Safety Valve (SSV) is installed in a flowline or onto a Xmas tree to shut down in case of an emergency and if the pressure in it is too high or too low. An SSV has several main components:
The control system takes fluids from the flowline or Xmas tree or valve flange through valves and pilots (pressure switches) to the actuator and controls all of the actions of the actuated valve according to the conditions in the flowline or Xmas tree.
The system has been designed to operate one high-pressure actuator mounted on a reverse acting gate valve with the control pressure coming from the flowline/pipeline. The maximum operating pressure will be 6000 psi gas of crude oil mixed with associated gas. The system has a high-pressure pilot installed to offer protection to the line or downstream installations. The low-pressure pilot will give protection for a lowpressure condition, which could indicate a broken line downstream of the system. Tattle tales are installed to indicate which pilot high or low, has been tripped. The system requires no electrical power or external power source other than flowline/pipeline pressure.
The valve is a full bore, through conduit, reverse acting gate valve, “RAGV”. The valve is called Reverse Acting because the gate of the valve is pushed into the flow stream in the well-bore or flow-line to open the valve. The through bore of the gate is at the same end as the stem. The stem passes through the packing seal in the bonnet and is attached to an actuator.
The actuator is a high-pressure, hydraulic, fail safe, spring return type. The actuator uses flowline fluids to push down the piston inside it, compress the spring, push the valve stem and open the valve. The valve will close when the flowline fluids are exhausted from the actuator. The fluids in the flowline push the against the valve stem, push up against the piston in the actuator and if the actuator is empty of fluids the valve will close. The spring in the actuator will close the valve fully if the flowline fluid pressure is too low. The flowline fluids are guided into or exhausted out of the actuator by the control system.