purge systems

[deadbunny]

I drive a 91 dodge cummins

How do you all have your purge systems set up. Im a little confused as to how they would be usefull as you would only be able to purge the system of WVO just before the stock filter on the cummins.

[VinDiesel]

Originally Posted by deadbunny

...as you would only be able to purge the system of WVO just before the stock filter on the cummins.

Sorry, I don't understand what you're saying. The Frybrid system (and in fact all other successful two-tank systems on here that I know of) does not share the stock diesel filter with both fuels. I can only surmise that is what you are talking about (?).

Part of the Frybrid setup is to re-plumb the original diesel filter to be on the suction side of the lift pump. A 3-port selector valve is used to switch between diesel and veggie. A heated VO filter, as well as a final flat plate heat exchanger, TIH (tube in hose) heated lines, and an in-tank heat exchanger/pickup are all on the veggie side of that valve.

On the return there is another 3-port that sends return from the IP and the re-located injector return back to either the VO or diesel tanks. During "purge" the supply valve is switched back to diesel while the return valve keeps returning to the VO tank for a pre-set time period (user adjustable). That way, incoming diesel displaces the VO and pushes it back to the VO tank.

A popular modification to this has become the "controlled loop". By adding a 3rd 3-port valve, return VO may be fed back to the lift pump inlet while in the veggie mode. At purge, this valve switches to return to tank, allowing the fast purge as before and sending any air bubbles that might exist back to the tank. This has proved to lessen vacuum on the lift pump and VO filter, making both happier.