Electronic pressure control pilot operated relief valve

A fluid pressure relief valve, comprising:

• a valve body having bores forming inlet and outlet ports and a fluid passageway therebetween;
• a valve seat in the inlet port;
• an axially bored valve head on the body opposite the valve seat, said valve head having a skirt projecting toward the valve seat,
• an axially bored piston valve slidably supported by the valve head skirt for movement toward and away from the valve seat,
• said valve head having axially offset first and second fluid passages respectively communicating with the outlet port and downstream limit of the valve head;
• a blind cylinder on said valve head having a wall forming a pressure chamber axially opposite the valve seat and having a third fluid passageway through the cylinder wall;
• a manifold having a valve chamber on the valve head providing fluid communication between the first, second and third fluid passageways through the valve chamber;
• a pilot operated three-way two position control valve in the manifold valve chamber;
• and,
• fluid pressure sensing means responsive to the fluid pressure in the blind cylinder pressure chamber for normally maintaining the pressure differential across said piston valve equalized and shifting said control [manifold] valve to exhaust fluid pressure downstream from the downstream limit of said piston valve in response to fluid pressure above a predetermined value.