The 106-RPS-RR and 206-RPS-RR surge anticipating relief on rate of rise valves are based on the 106-PG and 206-PG main valves. Each valve is installed downstream of the pump check valve(s) and has two pilots—the 81-RP and the 81-RPD. Both pilots sense pressure through a connection to the header pipe. The 81-RP high-pressure pilot acts as a standard relief pilot, opening on excessive pressure. The 81-RPD differential pilot responds to the pressure differential across its diaphragm. A pressure differential is created when system pressure increases. The flow into the accumulator creates a pressure drop across the fixed restriction, which lowers the pressure in the connection between the fixed restriction and the pilot.
