Self-actuated pilot-controlled safety valve

Claim 1

A self-actuated pilot-controlled pressure responsive valve for fluid pressure systems comprising: (a) a main pressure chamber having a main valve seat and a main valve disc normally seated thereon, and the back side of which is exposed directly to system pressure to force the disc against its seat to seal the pressure chamber from the outlet space; (b) a piston and cylinder assembly having its piston coupled to the main valve disc to impose thereon, when activated, opening forces exceeding the normal seating force; (c) first and second duct means to introduce substantially balanced fluid pressure from the system respectively into the cylinder on opposite sides of the piston; (d) a pilot valve assembly to operate the piston and interposed in a fluid path between the cylinder on one side of the piston and a pressure reference substantially below system pressure, including a pressure chamber connected to the cylinder, a pilot valve seat and a calibrated spring-biased pilot disc normally seated thereon against the chamber pressure whereby, upon opening in response to predetermined elevated system pressure, a pressure differential is established across the piston to unseat the main valve disc, a control disc seat and a control disc adapted to seat thereon interposed in a fluid path between system pressure and the said pressure chamber and forming part of the second duct means to one side of the piston, and means to connect the control disc to the pilot disc, whereby upon opening of the pilot disc valve the control disc seats under system pressure to isolate the chamber and one side of the piston from system pressure; and back pressure compensating means in the outlet space for the pilot valve and responsive to increased pressure in the outlet space to apply a force to the pilot disc opposing that derived from the back pressure.