STRUCTURE, FUNCTION, & MAINTENANCE STANDARD SELF PRESSURE REDUCING VALVE MAIN RELIEF VALVE (PC210/LC/NLC-7K) 1. Poppet 2. Spring 3. Piston Function The low set pressure and high set pressure can be changed by external pilot pressure. The relief pressure is determined by the pump pressure acting on poppet (1) and the set load of spring (2). When the pilot pressure is OFF, the system is set to low pressure. When the pilot pressure is ON, piston (3) is pushed fully to the left, so the force of the spring (2) increases and the relief pressure becomes the high set pressure. PC210/240-7K 10-87