The P1808 pilot-operated relief valve or back pressure regulator is used in gas or liquid service to maintain pressure on oil and gas separators, and in pressure relief applications in gas distribution systems. The function of the P1808 is controlled by the type of pilot installed on the unit. A PL82 series pilot regulator is used in back pressure applications, and only bleeds when repositioning the main valve. A PL82B series regulator is used in pressure relief applications, and exhausts the entire time the inlet pressure is above the set pressure. This allows the unit to achieve wide-open f low more easily. The unit controls pressures from 3 to 125 PSIG (0.21 to 8.6 Bar), and the set pressure can be adjusted for indi vidual requirements by the adjusting screw on the pilot.