Knowing Subsurface Safety Valve- API14A

Typical subsurface-controlled safety valve.
Early safety valves were relatively simple in
operation and created a significant restriction to
production. The force of the valve spring, FS, acts
on the flow tube to keep the flapper valve in a
normally open position. The pressure below the
restriction is P1 and that above is P2. These
pressures act on the exposed faces of the piston,
creating a force F1 – F2 to close the valve. When
fluid flows upward, the constriction creates a
pressure differential that increases closure
force. The spring force is preset for a specific
flow rate, so when the flow rate reaches that
critical rate, the piston moves up, releasing the
flapper to close and shut off fluid flow.
Charlie Chong/ Fion Zhang
https://www.slb.com/~/media/Files/resources/oilfield_review/ors02/win02/p52_64.pdf