🔍 Key Concepts
• Study how an oily water separator changes internal pressure in different modes: normal processing, bilge removal, purge, and backflush.
• Think about what happens at the top of the separator tank (where item "1" is located) during each mode—are you pushing liquid/air out, pulling in, or just venting?
• Relate a positive pressure reading on a gauge to whether the system is moving water through the coalescer or just clearing air/oil to a slop tank.
💭 Think About
• For each mode in the answer choices, ask yourself: would the separator tank need to be under positive pressure, negative pressure, or close to atmospheric at the location of item "1"?
• During which mode would flow be strongest through the separator media, and during which would it be directed backwards or mainly to a vent/slop line?
• If you were only removing air from the top of the tank, what would you expect the pressure gauge to read—above, below, or near atmospheric pressure?
✅ Before You Answer
• Identify exactly where item "1" is located in the system (top of separator tank, on a vent/line, etc.).
• For each mode, trace the direction of flow (from pump, through separator, to overboard or slop tank) and decide if that would create positive pressure at item "1".
• Eliminate any modes where the tank top should be vented or near atmospheric pressure, because those are inconsistent with a clearly positive pressure reading.