Your Safety valves valve is a direct spring-loaded pressure-relief valve that is opened by the static pressure upstream of the valve and characterized by rapid opening or pop action.

When the static inlet pressure reaches the set pressure, it will increase the pressure upstream of the disk and overcome the spring force on the disk.

Fluid will then enter the huddling chamber, providing additional opening force.

This will cause the disk to lift and provide full opening at minimal overpressure.

The closing pressure will be less than the set pressure and will be reached after the blowdown phase is completed.