Surface controlled subsurface safety valve with annular seal

A subsurface safety valve (SSV) or plug 510 is disclosed. The plug includes a seal assembly 514, 516 located around the circumference of the plug for sealing the void between the plug and the production tubing 500 in which it is located. The seal is compressed by a piston 504. Wellbore fluid pressure acts on the piston from below when the valve is closed, thereby moving the piston to force the seal into sealing contact with an inside surface of the tubing. A drainage path 505 is provided above the piston for draining the pressurized fluid above the seal. An interlock comprising locking dogs 509 may be provided for locating the plug within the wellbore. The seal may be located between first and second chevrons 512, 514.