MODE OF OPERATION

The safety valves system is designed to accomodate stainless steel tubing connections interwoven to form a closed loop. The instrument air from the regulator to the supply inlet of the sigma valve keeps the u-valve permanently open and maintain a pressure in the pilot.The pilot has a calibrated range of low and high and to obtain each parameter for calibration,the flowline pressure has to be determined. Note that the high pressure range is obtained in the wellhead through the crown valve,whereas the low pressure of the well is obtained through the wing valve of the flowline.These classification as low and high  are sometimes refer as downstream and upstream pressure,depending on the operators.Therefore the pilot is calibrated at 75% of the flowline pressures both for low and high, however any variation arising from flow causes a bleed off pressure from the sigma valve.The u-valve is actuated by this variation which the p-pilot transduced.This automatically close the gate of the u-valve actuator,thereby shutting off the flowline.The plug is also for safety purpose,and its action occurs when there is risk of fire in the well.As the temperature of gas and pressure increases. the lead in the fusible plug will met and creates a vent for pressure escape; and automatically the u-valve will be actuated thereby close or shut-in the flow.