Pilot-operated safety valve works: When the system pressure is lower than the set pressure of the valve, the medium pressure is transmitted through the pilot valve to the main valve pressure chamber, acting on the main valve flap, resulting in downward force to close the main valve; When the system pressure increases close to the set pressure, the pilot piston lifts and closes the upper seal, at which point the pilot lower seal is still closed. System pressure is slightly increased, the next seal micro-Kai, the pressure in the main valve pressure chamber through the pilot valve to exclude the vent; when the system pressure reaches slightly higher than the set pressure when the pilot valve seal open, overpressure relief, which in turn leads to Valve piston tends to fall. This feedback can float the main valve flap in a certain position, to adjust the role; when the system pressure overpressure, the main valve flap to fully open; when the system pressure drops below the set pressure, the pilot valve seal closed. Pressure is further reduced to return to the pressure chamber pressure, turn off the main valve.