Pilot operated safety relief valve

A pilot operated safety relief valve assembly comprising:

• a main relief valve including a main valve body having a main valve chamber, an inlet flow passage extending axially from an inner end of said valve body to said main valve chamber and defining an annular valve seat about said inlet flow passage, and an outlet flow passage extending axially from one side of said valve body to said main valve chamber at right angles to said inlet flow passage;
• said valve body having a generally planar outer end face in opposed relation to said inner end to define an outer end of said main valve chamber, and a generally planar side mounting face in opposed relation to said one side and said outlet flow passage;
• a generally cylindrical main relief valve mounted in said valve chamber for reciprocal movement axially of said inlet flow passage and for seating on said annular valve seat with a dome chamber defined between said main relief valve and said planar outer end face,
• a removable outer end cover plate mounted on said planar outer end face to permit removal of said main relief valve member from said planar outer end face upon removal of said cover plate, said cover plate forming an outer end of said dome chamber at said planar outer end face;
• a pilot valve having a separate pilot valve body and a pilot valve member mounted in said pilot valve body;
• said pilot valve body having a planar side mounting face opposed in mating face to face contact with said planar side face on said valve body;
• a dome passage from said pilot valve to said dome chamber extending through said opposed planar side mounting faces;
• an exhaust passage from said pilot valve to said outlet flow passage extending through said opposed planar side mounting faces and said valve chamber for the exhaust of fluid from said dome chamber to said outlet flow passage upon the actuation of said pilot valve member;
• an inlet sensing passage from said inlet flow passage to said pilot valve member for the actuation of said pilot valve member upon the reaching of a predetermined high fluid pressure in said inlet flow passage thereby to permit the exhaust of fluid from said dome chamber to said outlet flow passage through said opposed planar mounting faces;
• means securing said pilot valve body to said main valve body with said opposed planar side mounting faces in face to face contact with each other;
• said pilot valve body having a bore (206A) therein in fluid communication with said dome fluid passage and said exhaust fluid passage;
• and
• a freely movable fluid pressure responsive back flow valve piston (121A) disposed within said bore (206A) for movement between two positions, said piston in one of said positions being responsive to fluid pressure from said dome chamber greater than fluid pressure in said outlet flow passage to prevent direct fluid communication between said dome passage and said exhaust passage, and in the other of said positions being responsive to fluid pressure in said outlet flow passage greater than fluid pressure in said dome passage to permit direct fluid communication between said dome passage and said valve chamber through said exhaust passage which extends through said opposed planar side mounting faces.