Diesel Engine Fuel Pump Replacement Seal-less & Seamless

By George Backwell at July 08, 2012 05:28
Filed Under: General

PSC boarding officers want to see a generally clean engine-room when they go down the ladders, then take a more careful look for signs of oil leakage from fuel transfer pumps close by hot surfaces.

The problem for the chief engineer though is that traditional shaft-sealed fuel pumps inevitably will drip, mainly due to the increased viscosity and temperature of the kind of latter-day HFO bunkers they deliver. Nevertheless, with new technology, constantly leaking fuel pumps and negative inspection reports can be avoided.

Best answer seems to be to fit seal-less magnetic drive pumps (which have no outside shaft) as did the Moby Line when they recently ordered  fourteen of Colfax’s Optiline heavy Colfax fuel oil transfer pumps to retrofit in the engine rooms of its ferry fleet.

Seal-less Pumps

A packing box, mechanical seal or lip seal are the best known methods of avoiding leakage around a rotating shaft that extends through the wall of the pump. The seal-less magnetic drive pump on the other hand utilises an entirely different method as will be seen.

A cylindrical hub with high-strength magnets  (canned by a non-magnetic material) is mounted on the rotor shaft. This hub is surrounded in turn by another cylindrical hub (also canned) whose interior is similarly lined with high-strength magnets coupled to the drive shaft.
As this outer hub rotates the magnetic fields of the two hubs are engaged, and by this means the pump shaft rotates without any physical connection to the drive and thus no need for a dynamic shaft seal whatsoever. These components are shown below.

Seal-less Pump Magnetic Coupling: Image courtesy of Colfax/Micropump Inc.

Colfax's Optiline pumps are designed to handle heavy fuel oil transfer at temperatures up to 350 degrees. Cooling is achieved by diverting a small fraction of the pump flow back to the inner side of of the magnetic coupling for return to the pump inlet. 

The manufacturers say that the consequent minimal loss of flow has no practical impact but removes the heat generated in the coupling without any need for external cooling.

Moby Line Colfax Pump  Retrofit

Moby Line Cruise Ferry: Photo courtesy of Moby Line

Moby Line, which operates a fleet of ferries between mainland Italy and islands in the Upper Tirenian Sea, took delivery of the new seal-less Optiline pumps as a drop-in replacement for their present IMO AB three-screw axial pumps. According to Colfax, this kind of installation takes just a few hours to complete in port.



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