Emmie to the rescue of leaking seals

01 Dec 1999

Many ship operators know the feeling. Analysis returns show that the water content of the stern tube oil climbed well above acceptable levels and suggests that the seal has started to leak. Traditionally the cure was an unscheduled drydocking and replacing the seal, but there may be another option in the form of Emmie, a mobile centrifugal separation system from Alfa-Laval.

Stern tube aft seals are designed to minimise leakage, in either direction, and normally they do their job well but fishing nets, a long cable or wire, or floating waste can damage them in seconds. As the water content in the sterntube oil rises, so does the problems for the operator. Changing the oil for a more sophisticated lubricant that can tolerate high water levels may help but, in the end, too much water in the stern tube oil means only one thing - into dry dock as soon as possible and repair the aft seal. For all ship operators, unscheduled dry-docking is a nightmare: the docking charges are higher than when planned and the off-hire losses can be huge.

Alfa-Laval`s Emmie is a mobile centrifugal separation system designed to be used on small volume gear and hydraulic oil systems found on board modern vessels. Weighing less than 60kg, the separator unit is trolley mounted for mobility and can be taken up and down steep stairways. The unit consists of a solid bowl separator complete with motor, pump, starting gear and a collecting tank for bowl drain oil or separated water. A 34kg heater trolley is designed to heat incoming oil up to 65 degC maximum and, like the separator trolley, is powered from a 230/110V supply.

Once the separator and heater trolleys are in place, it takes as little as five minutes to connect it to the tank using standard hydraulic hoses with quick release couplings and non-return valves. Where the tank has not been fitted with the relevant connections, the suction and return lines can be lowered into the tank through the filler cap opening. Once the oil is flowing through the separator, the heater can be turned on. Alfa Laval recommends that the whole system volume is circulated through Emmie five times but where water has emulsified into the oil this then rises to 35 passes. Emmie can process between 50 and 150 litres/hr and is adjusted using the in-built frequency converter controlling the Imo feed pump motor speed. To determine the required flow rate, the operator times how long it takes the oil to flow into a measuring cap mounted on the separator unit. This time is then cross referenced on a chart to find the required flow rate.

Bowl cleaning takes about five minutes and on a typical hydraulic oil application, is required after one to three days operation. If the oil is known to contain water, the bowl can be converted from clarifier to purifier configuration and the removed water will drain into the collecting tank.

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