The Tubing Retrievable Safety Valve, always positioned subsea, is a component of the production tubing, and a safe way to prevent blows or uncontrolled well flows, in the event of a failure in the surface safety equipment, preserving the environment and people's lives.
The valve is normally closed, controlled from the surface. For allowing production the DHSV has to stand in the open position. It also allows the installation of a Wireline Retrievable Safety Valve. Both can be self-equalizing or non-equalizing.