How many LO relief valves are at each pump and what is their lift setting?

• A. Two relief valves; lift at 140 PSIG
• B. Three relief valves; lift at 120 PSIG
• C. Four relief valves; lift at 110 PSIG
• D. Three relief valves; lift at 100 PSIG

Answer: (B)

Relief valves in the LO (lube oil) path are there to prevent overpressure and protect the pump and bearings by dumping excess oil back to the sump when the pressure climbs above a safe limit. In this arrangement, each pump has three relief valves, and they are set to lift at 120 PSIG. This combination provides enough relief capacity to handle different flow demands and start-up surges, while keeping system pressure within a safe, narrow range during normal operation. A setting of 120 PSIG is high enough to ensure proper lubrication pressure during operation but low enough to open before pressures reach damaging levels; having three valves ensures reliable relief even if one valve’s performance changes with wear or temperature. The other options would either set the opening pressure too low (causing unnecessary bypass and low lubrication pressure) or too high (risking overpressure), and they don’t align with the standard LO relief-valve configuration for each pump.