Fuel Treatment Plant Schematic

Fuel is drawn from the tank and goes through the 150 micron screen. This is a small clear chamber and is designed to catch any big lumpy bits.

Next up is the manual priming pump with a bypass valve. In normal operation, the bypass valve is open allowing the fuel to pass freely. Close the valve and all flow must go through the pump. This is just your standard large bulb priming pump and allows fuel to be pushed through the system right up to the engine.

Fuel enters the Delphi system. This has two valves to allow this filter to be bypassed if it is causing problems or the element needs changing while the engine needs to keep running. The Delphi filter is nominally 7 microns and has a water trap to pick up any moisture. These filters are cheap as chips and make excellent first stages.

The next system, the Racor, is essentially the same as the Delphi. This has a 2 micron filter and is the final stage in the plant. This can also be isolated.

I have put a vacuum gauge on the engine line. This is used to indicate when the filters are becoming blocked and the elements need changing. This reads from 0-30" Hg (essentially no vacuum to a bit of vacuum) and experience suggests that, when all is well, it sould read around 5" Hg. Its reading and what that means depends on what filters are switched in and their condition.

Once the fuel has passed through the filters, it gets to the circulation pump and its isolation valves. The valves either send the fuel to the engine or straight back to the fuel tank - in other words, this is the fuel polishing loop.

Fuel polishing, as far as I can tell, is a bit of a last resort for a couple of reasons. Firstly, diesel engines draw much more fuel from the tank than they actually use. The fuel return line is what sends it back. If the fuel has been through a good filtration system, this returned fuel will be in excellent condition. In other words, fuel is being continually polished while the engine is running - assuming your filters are good. The fuel would have to be in a very bad way for specific polishing to make a huge difference - though, if it is in that bad a way, a polishing setup is just what you would want.

Up

>