Pilot type solenoid valve

Claim 1

A FLUID PRESSURE CONTROL DEVICE COMPRISING A HOUSING HAVING A HOLLOW CYLINDRICAL CHAMBER, A PLATE OF MAGNETIC MATERIAL SUBSTANTIALLY CLOSING ONE END OF SAID CHAMBER AND AN INLET PORT IN SAID HOUSING CONNECTED WITH A SOURCE OF FLUID UNDER PRESSURE, AN OUTLET PORT AT THE OPPOSITE END OF SAID CHAMBER CONNECTED TO A SOURCE OF LOWER FLUID PRESSURE, A VALVE SEAT AT SAID OUTLET PORT, A PISTON HAVING A WALL SUBSTANTIALLY CLOSING ONE END AND A SHOULDER OF SUBSTANTIAL EFFECTIVE AREA BUT LESS AREA THAN SAID WALL ON THE OPPOSITE END ADJACENT SAID INLET PORT RECIPROCABLE IN SAID HOUSING PARALLEL TO THE AXIS THEREOF AND A VALVE MEMBER FORMING PART OF SAID PISTON ADAPTED TO ENGAGE SAID VALVE SEAT, A CYLINDRICAL EXTENSION OF SAID PISTON ATTACHED TO SAID WALL INCLUDING A CYLINDRICAL SECTION OF NON-MAGNETIC MATERIAL AND A PORTION OF MAGNETIC MATERIAL, A COIL AND A COIL FORM MEMBER INCLUDING A CYLINDRICAL SECTION OF NON-MAGNETIC MATERIAL CONCENTRICALLY POSITIONED IN SAID HOUSING OUTSIDE OF SAID EXTENSION, AN ORIFICE IN SAID WALL AND A PILOT VALVE MEMBER ADAPTED TO CONTROL THE FLOW THROUGH SAID ORIFICE, AN ARMATURE RECIPROCABLE IN SAID EXTENSION THREADEDLY ENGAGED WITH SAID PILOT VALVE MEMBER, A POLE PIECE ABUTTING AGAINST