Stepped pressure gas valve apparatus

A pressure responsive shut-off valve comprising:

• a valve housing means defining a fluid inlet and a fluid outlet and a valve seat therebetween;
• a valve closure means movable between a closed position against said valve seat and an open position away therefrom, said closure means preventing fluid flow between said inlet and outlet when in said closed position and permitting said fluid flow when in said open position;
• a valve operator means comprising a pressure responsive piston movable between set and release positions, said operator means coupled to said valve closure means so as to effect location thereof in said open position with said piston in said set position and location thereof in said closed position with said piston in said release position;
• a cylindrical magnetic plunger mounted for reciprocable movement in said housing means and retaining said piston, said plunger defining an activating volume communicating with said inlet and establishing an activating fluid pressure on one face of said piston, said activating fluid pressure forcing said piston toward said release position, said plunger further defining a reference volume communicating with said inlet and establishing a reference volume on the opposite face of said piston;
• a bias spring member disposed in said activating volume and having one end coupled to said piston and an opposite end directly connected to said housing means, said spring member urging said valve operator means in a direction to produce movement of said valve closure means to said closed position;
• a seal means for sealing said inlet from said reference volume with said piston in said set position and providing fluid communication therebetween with said piston in said release position;
• latching means for latching said piston in said set position;
• and
• manual reset means for moving said piston from said release position to said set position.