Re: Changed my mind about fuel polishing

Two meter troll wrote:

his fuel polishing system disallows this if he wants a proper fuel
line pressure in all cases. his decision, his boat. pointing out
options was my idea.

I appreciate the suggestions. However, for sake of discussion and anyone looking at it for ideas on their sailboat:

(Schematic of my system here: http://home.roadrunner.com/~rlma/StriderFuelSystem.htm)

My system is a very tolerant, low pressure system. It runs from the main tank quite well with gravity feed alone up to the mechanical fuel pump. The mechanical fuel pump draws quite well from the low tank with the electric fuel pump turned off but the vacuum is higher than I would like to subject the pump to for long periods.

The pressure head at the mechanical pump inlet is the same when running off the bypass as it is when gravity feeding from the main tank. If this should be insufficient due to the secondary engine mounted filter starting to load up or a fault in the mechanical fuel pump, I can gradually close the isolation valve to force fuel to the engine at up to the full pressure that the polishing pump can develop. This pump BTW does not have the pressure cut off and regulation feature of a normal FO lift pump.

In a single tank installation with a bilge tank significantly below the engines and fuel system, there might not be sufficient fuel pressure and partial closing of the isolation valve might be necessary. In my case though, I get normal fuel line pressure in all cases as well as the option of increasing it.

It's worth repeating Rich H's brilliant idea for further redundancy:

The fuel polishing line runs to a small gravity feed tank that contains 1 - 2 hours of fuel. The line goes in the bottom of the tank from the polishing system and exits the top on its way back to the main tank. A line runs from this tank directly to the engine bypassing the engine driven fuel pump and the vent has a valve on it. The fuel line could also bypass the engine mounted fuel pump in some installations but not on mine since the injector return line goes back to the filter instead of the tank, a Yanmar oddity. This tank is constantly being filled, flushed, and renewed with just filtered fuel that doesn't sit in the tank when the engine is running. If all else fails, just open the supply and valves and a supply of clean fuel sufficient to get the vessel out of trouble or change filters goes directly to the engine.

In any event, I can change filters alternately on my system until I run out of elements so I'm pretty well covered for the worst case situation. I've also got those sails:)

--
Roger Long


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