Pilot operated relief valve

In a pilot for operating a main valve to relieve product pressure in predetermined proportion to the pressure excess of the type utilizing continuous product venting, and a flow restrictor to position the piston of the main valve wherein said main valve is of the type having a pressure balanced moveable closure member, and a pressurized head volume thereabove, the improvement comprising;

• a valve body;
• a pressure sensitive poppet in said body having a first diameter, and adapted for reciprocal motion therein comprising;
• an upper end with an extending stem having a second diameter, said second diameter substantially less than said first diameter, and defining an annular pressure sensitive area;
• a lower end defining an effective pressure sensing area greater than said annular area;
• a passage in said poppet communicating said areas for equalizing upper and lower area pressures exerted on said poppet;
• means sensing product pressure and adapted to position said poppet during relief operation;
• means pressure sealing said poppet end and stem comprising;
• a reciprocating poppet seal attendant said first diameter generating a first seal stiction force;
• a reciprocating stem seal attendant said second diameter generating a second seal stiction force;
• seat means in said body coating with said poppet lower end comprising;
• a poppet seat having an effective flow diameter substantially greater than said stem seal diameter, said poppet seat, poppet and stem seals providing decreased stiction and thereby increased pilot product flow through said poppet seat for poppet positions corresponding to overpressure;
• wherein equalized product pressure acting on said poppet providing a net upward force and said decreased stiction improve poppet stability, thereby increasing relief valve capacity for said overpressure;
• and,
• a sensing volume in said body;
• a test port in said body;
• means fluid communicating said test port, seat means, and sensing volume;
• guide means in said communicating means intermediate said test port, sensing volume, and seat means;
• a flow sensitive closure member contained in said guide means and adapted for reciprocal motion therein, said closure member sealing said test port or seat means at either extreme of its motion, and maintaining communication withe said volume;
• wherein introduction of test vapor at a pressure greater than said product pressure isolates said seat means, thereby
• providing pilot operation without increasing product pressure.