Referring to the illustration, suppose after initiating the oil discharge mode, the oily- water separator fails to come out of the oil discharge mode in a timely fashion. Cracking open the upper sampling valve reveals the presence of oil exiting under positive pressure. What is most likely the cause? Illustration GS-0175

Correct Answer: Option B — The oil discharge check valve fails to open, and as a result no oil actually discharges.

If the system remains in oil discharge mode but oil is present at the sampling valve, the discharge path is obstructed. A failed check valve prevents the oil from leaving the vessel, causing the system to stall in the discharge phase despite the probe correctly identifying the oil presence.