Knowing Subsurface Safety Valve- API14A

In principle, a safety valve is a simple device. Most of the time it is open to
allow flow of produced fluids, but in an emergency situation it automatically
closes and stops that flow. To effect this task, sophisticated engineering
designs and state-of-the-art materials have been developed. The valve’s
closure mechanism must close and seal after months of sitting in the open
position and years after its installation.
Special procedures and technologies applied to reopening the valve after
closure ensure its continued reliability. Wells are drilled and completed under
diverse conditions, so before an appropriate subsurface safety valve is
selected and installed, a thorough review of the reservoir, wellbore and
environmental conditions must be conducted.
Charlie Chong/ Fion Zhang
https://www.slb.com/~/media/Files/resources/oilfield_review/ors02/win02/p52_64.pdf