Tubing Retrievable Surface Controlled Sub Surface Safety Valves form part of production string. Hydraulic control line extending from the valve to the Wellhead connects to a part on the outside of the valve. The opposite end of the control line connects to the Wellhead. Hydraulic pressure applied through this control line acts on hydraulic pistons within the valve. The force generated moves the flow tube down against a power spring and tubing pressure, causing the flapper to open. Maintaining this hydraulic pressure allows unrestricted well production through the valve. Releasing the hydraulic pressure causes the flow tube to move up by the action of the power spring, thus allowing the flapper to the closed position.