Pilot operated relief valve

A valve assembly for relieving the fluid pressure in a pressure vessel comprising:

• a main body having an inlet, a main valve chamber, and an outlet;
• a piston mounted in said main valve chamber for reciprocal movement between open and closed positions relative to said inlet for fluid pressure relief of said pressure vessel;
• a dome chamber adjacent an outer end of said piston;
• and
• a pilot valve structure mounted on said main body in axial alignment with said piston and forming an outer end of said dome chamber;
• said pilot valve structure including a diaphragm, an inlet fluid sensing chamber on one side of said diaphragm, an exhaust chamber between said inlet fluid sensing chamber and said exhaust chamber, and a fluid inlet sensing member extending from said piston to said inlet fluid sensing chamber;
• said piston having a central bore therein in fluid communication with said inlet, and said fluid inlet sensing member having a lower end portion received within said central bore communicating inlet fluid to said inlet fluid sensing chamber.

A pilot valve structure arranged for mounting on an end cap adjacent a dome chamber on a valve body for a main safety relief valve;

• said pilot valve structure comprising:
• pilot valve body having an opening therein;
• a sensing tube for inlet fluid extending through said opening and having a lower end portion extending through said dome chamber to said main safety relief valve;
• a diaphragm secured to an upper end portion of said sensing tube;
• an inlet fluid sensing chamber adjacent an outer side of said diaphragm;
• an exhaust chamber in said valve body between said inlet fluid sensing chamber and said dome chamber including an exhaust port;
• and
• a pilot valve member within said dome chamber between said sensing tube and said pilot valve body movable between seated and unseated positions to control the flow of fluid between said exhaust chamber and said dome chamber of the main safety relief valve.

A fluid pressure relief valve for relieving the fluid pressure in a pressure vessel comprising:

• a main body having an inlet, a main valve chamber, and an outlet;
• a main piston valve member mounted in said main valve chamber for reciprocal movement between open and closed positions relative to said inlet for fluid pressure relief of said pressure vessel, said piston valve member being of a generally cylindrical shape and having an axial bore therethrough;
• a cap mounted on said main body in opposed relation to said outer end of said piston valve member, said cap having a central opening therein in axial alignment with said axial bore of said piston valve member;
• a dome chamber formed between said cap and said outer end of said piston valve member;
• and
• a pilot valve mounted on said cap and having an inlet fluid sensing tube extending through said central opening in said cap and into said axial bore of said piston valve member with a restricted annular clearance between said tube and said piston valve member to permit a restricted inlet fluid flow from said inlet to said dome chamber.