🔍 Key Concepts

• Operation of a centrifugal or gear-type lube oil pump in a marine engine system • Difference between suction side problems and discharge side problems in pumps • Effect of valve positions and system resistance on a pump’s ability to build pressure

💭 Think About

• Ask yourself: if the pump is running but cannot build discharge pressure, is the problem more likely on the suction side (getting oil into the pump) or the discharge side (pushing oil out)? • Which valve condition would allow oil to simply circulate or not enter the pump correctly, preventing pressure buildup at the discharge gauge? • What does a high suction vacuum usually indicate about the condition of the suction line (e.g., restrictions, closed valves, clogged strainers)?

✅ Before You Answer

• Identify which options describe a problem on the suction side versus the discharge side of the pump. • Consider what happens to discharge pressure if the suction valve is not open enough for oil to enter the pump. • Think about whether a closed bypass valve or open discharge valve would actually stop pressure from building, or just change the flow path/pressure level.