With reference to Oily Water Separators and the pumping of bilges, explain the purpose of EACH of the following: (a) a bilge holding tank;(2) (b) an oil drain tank;(2) (c) an oil content discharge monitor;(2) (d) a vacuum breaker;(2) (e) an oil detection probe.(2)
(a) Bilge holding tank (2 marks)
Purpose: To temporarily store bilge water before treatment.
Reason: Allows controlled transfer to the OWS at a regulated rate, ensuring efficient separation and compliance with 15 ppm discharge standards.
(b) Oil drain tank (2 marks)
Purpose: To collect oil drained from machinery sumps, separators, filters, and settling/ service tanks.
Reason: Prevents direct entry of oil into bilges and ensures proper disposal or incineration in line with MARPOL requirements.
(c) Oil content discharge monitor (2 marks)
Purpose: Continuously measures the oil concentration in effluent leaving the OWS.
Reason: Ensures discharge is only permitted if oil content is ≤15 ppm; provides alarm and automatic stop function if above the limit.
(d) Vacuum breaker (2 marks)
Purpose: Fitted on the discharge line to prevent siphoning and backflow into the OWS.
Reason: Protects equipment and ensures that oil-contaminated water cannot re-enter the bilges or machinery spaces.
(e) Oil detection probe (2 marks)
Purpose: Detects the presence of oil in water inside tanks or separators.
Reason: Provides feedback to control systems (e.g., automatic 3-way valves) to divert oily mixtures back to bilge holding or oil drain tanks until clean water conditions are met.
