Hi Ho howday all... been working toward getting my conversion underway for de ole bus, been doing much research on veggie oil. One of the things that they have been talking about is looping the return lines. This raised a question . . .

Does the IP need a pressure difference between supply and return line? If you "loop" the return back into the supply line, will that cause problems, (excluding of course any air problems)? Or is the purpose of the lift pump only to get it to the IP, and return doesn't make a hill of beans?

Don't know exactly what is meant by 'loop', but they are probably trying to utilize normal heat and 'homogenization' from Inj Pump to keep the stuff flowable under all conditions.

As you know, any pump's pressure output is based on input pressure - A 7psi pump will output 14psi if input is 7psi.

The line from the tank has no check-valve, so the return flow would take the path of least resistance.

I'm not sure I understand what your 'looping' either. Sounds like your going to have supply pressure on the return side of the system? I would highly reccommend against this, won't do any damage to the pump at all, it maintains housing pressure of 8-16psi and just vents the rest to the return, but your going to create a leak in the return lines off the injectors for sure, they barely last with the minimal pressure they get with stock setup, they won't hold pressure.

As best as I understood this, it was dumping the return line back into the supply line, instead of the tank. I understood what they were attempting to do here with keeping the heated WVO going to the IP, instead of constantly warming up the whole entire tank. I was a little amiss about where the lift pump was at in this whole scheme of things too. Seems to me, if you loop your return, if you ever got any air in the system, it would never purge without pulling the lines and purging them.

The other thing too was that if your supply and return pressure were equal, that would equal no flow in my mind. Your average 2 liter of soda is under pressure, but no movement, because no pressure difference, until you've cracked the lid and create a "vacuum" shall we say. Then you've got flow all over your BVD's while driving down the road. Not mention all the flow jokes that will come out after looking like you just wet yourself, but anyway. Make any sense?

Your right, this system has serious disadvantages. Better off using a seperate heated tank for WVO IMHO.

You loop the return line to the inlet side of the electric supply pump and install a small bleed orvice at the highest point to rid the system of air. The return line then must be routed into the tank to the bottom to prevent sucking air back thru the orvice or install a one-way check valve in the return. The DS pump already incorporates a semi closed loop return in the pump itself as the fuel goes thru the head it goes back to the inlet side of the inlet unlike most injection systems.

I don't see how this will work for a WVO system, dont you have to have a seperate tank for diesel and WVO?

Yepper, two tanks with that setup. You've got to use switching valves to keep your supply and returns going in the right direction. The "looping" from my understanding is only in the WVO fuel system.

I think the best solution is just to use a heated secondary WVO tank. You want to keep ALL the veggie oil hot and fluid right?

Abbasollutily. Keep that veggie oil thinned out a best as possible. I'm building a heat exchanger right now that should be able to heat the oil to it's full temp (around 150°F) before the IP.

So, how much fuel comes back on the return line in the system anyway? Say at idle? I assume more fuel comes back on the return line at low idle no load conditions than WOT on the highway? I was just wondering how quickly the return fuel will heat the whole tank up?