In addition to the abbreviation listed in API 17D the following are used in this standard: SCSSV. Surface Controlled Sub-Surface Safety Valve. LWRP. Lower Workover Riser Package ... The tubing hanger running tool shall as a minimum have the following functions: o operating of SCSSV (pressure rating to be given by Company) ... The ST shall have pressure monitoring functions in the production bores. 5.17 Horizontal Subsea X-mas Tree System ...

This ball valve assembly consists of a ball, seat, control arms, sleeve weldment (with guide and drive pins), and alignment pins; the ball is provided with slots to accommodate the drive pins. The operation of the ball valve assembly is as follows. Downward movement of the valve seat and control arms within the sleeve weldment will move the ball downwards. This downward movement causes a 90o rotation of the ball to the open position due to the (stationary) drive pins; guide pins ensure that this rotation occurs in the same plane. The reverse of the above action will close the valve assembly.
To open the valve, hydraulic pressure greater than the well pressure is applied to move the piston downwards by concentric piston actuation. With the valve seat screwed directly to the lower end of the piston this downward movement will offseat the secondary valve and expose the equalisation ports allowing well pressure to equalise across the valve. This minimises the possibility of damage to primary sealing surfaces when opening the valve. As additional pressure is applied, the piston continues its downward movement, the sleeve weldment butts up against the body, and the ball rotates to the open position. The ‘wiping’ action of the ball across the seat ensures a good clean sealing surface.

Upon loss of hydraulic pressure, the power spring is designed to lift the hydraulic head of control fluid and mechanically rotate the ball into a closed position by the reverse of the above action.