The “Forgotten” Rubber Membranes


 Not many seafarers did pay attention to this membrane which prevents anything from entering the diesel engine’s lube oil sump.  The Main engine bed plate, the tank top – lube oil sump are framed together – however there exists a space through which the water or any other liquid which can enter the main engine lube oil sump, causing contamination and further damages.  This critical area is often neglected or uninspected.

In fact, many seafarers are not aware of this rubber membrane or its location.  The ever increasing commercial pressures and shorter port stays contribute to a major factor, where the ship staffs overlook this critical area which has to be inspected periodically.

Major engine makers like Wärtsilä/Sulzer & MAN Diesel & Turbo have released various circulars and service letters recommending inspection and regular checks on these rubber membranes.  The Swedish club reports that in one of the cases, the rubber membranes were not oil resistant, which eventually caused complete failure of the membranes.  In other cases the rubber membranes failed due to natural aging process.


In both cases described above excessive quantities of water on the tank top entered the main engine sump tank and subsequently contaminated the main engine lubricating oil system, resulting in severe damage to the main engine bearings.  Weather it being the aging or the non-resistant to oil feature that triggers the failure of the membranes, is of less importance.  The mere fact that these “forgotten” parts of the machinery can result in serious losses to owners.


How to avoid Failure of Rubber Membranes:

  1. It is rather clear that the design of Wärtsilä/Sulzer and MAN Diesel A/S in this respect are similar, and as a consequence they are both potentially exposed.
  2. The Swedish Club emphasizes that the actual parts in question, during commissioning of the ship, are supplied by the yard, and not by the engine manufacturers.
  3. Wärtsilä/Sulzer’s recommendation is as follows: Inspection of this part at 40,000 running hours, during a dry dock and replace it if it’s damaged.


MAN Diesel A/S, Copenhagen, has recently issued a more comprehensive recommendation to replace all membranes in connection with each dry-docking of the vessel.

MAN Diesel A/S, Copenhagen, recommends: in order to avoid water entering the main engine sump tank through a defect in the crankcase oil outlet:

  • Inspect the diaphragm sealing in crankcase oil outlet every 32,000 hours of operation and replace the diaphragm if it is indicated by the observation.  Always replace in case of a rubber diaphragm.
  • Inspect the diaphragm sealing at the earliest opportunity after delivery of a new-building.  In case of a rubber diaphragm make sure the material is oil resistant and replace if this is not the case.
  • Inspect the diaphragm sealing at the earliest opportunity when taking delivery of an existing ship and replace the diaphragm if it is indicated by the observation.  Always replace in case of a rubber diaphragm.

What Could be the Cost of Such Rubber Membranes?

Typically the size and the number of outlets on an engine decides the cost of the rubber membranes.  However a ‘Ball-Park’ price of USD 1000 to USD 3000 can be the cost of a single rubber membrane.  We would recommend to owners that spare membranes are kept onboard at all times.

Would you like to share your best Engineering tip to inspect these Rubber Membranes or other interesting stories, do write to us with your name and Photgraph to Our E- Mail


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