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how to best use lift pump(s) -design help needed
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hey guys, I am about to modify a 1998 12 valve dodge/Cummins truck here.

I get so many mixed stories about how good the original lift pump is, I am wondering if I should have a seperate lift pump for the Veg. system, and/or how to plumb the fuel system to make it work most effectively.

I plan to use a VO Controller to monitor and manage the Veg system because this truck will be driven by various drivers in my business, and I don't trust them all to remember how/when to switch over to veg, purge, etc. So I need a hands-off system as much as possible, and the VO Controller should meet my needs.

Now my main question is about the lift pump(s) If I use the original lift pump, I would need 2x 3 way valves on the supply side of the injection pump right? one valve before the lift pump to controll whether diesel or Veg is supplied. Then another valve to send the fuel out of the lift pump into either the diesel filter, or the veg filter/FPHE, etc. Correct? Then have 1 valve in the return line which directs fuel back to diesel or veg tank. I see from sunwizards system here
http://www.burnveg.com/forum/viewtopic.php?t=28 that the return line also loops back to the supply line, and would allow a looped return, but only require 1 valve to do this and have the purge still work since the fuel returning would flow back through the veg supply side back into the veg tank. (hope you see this post SunWizard and can confirm this for me)

If I do stay with using only one lift pump, and the VO Controller, how do I deal with the little bit of veg left in the lift pump when you switch back to diesel? As soon as the purge begins, the supply valves would be turned to diesel and the veg left in the lift pump would go through the diesel filter and would require longer to reach a good thorough purge. I talked to the guys at VO Controll and they suggest not using the same lift pump or filter for diesel and veg. I agree it is ideal, but unless I buy another lift pump to supply the Veg, I don't see any way around having that bit of contamination of Veg left in the lift pump going through the diesel filter.


And if I do get another lift pump (FASS or equivalent) I am not sure how to deal with the stock lift pump. It is mechanically driven and probably shouldn't be dead-headed which would happen if it's still running and blocked by a valve that turns fuel flow over to the veg system. So how do I run 2 lift pumps without burning one up?

The only ideal solution I can see is to take out the original lift pump and buy two electric lift pumps, as the VO Controller is designed to send power to one of 2 electric lift pumps. But being a 12 valve Cummins requiring fairly high pressure at the injection pump, we're talking a lot of money to buy 2 FASS pumps.

How do people hook their fuel system up when using a lift pump? Do you just not worry about the little bit of contamination of veg that goes through your diesel filter? just run longer purge times?

Any thoughts/ideas are greatly appreciated!


1986 vw jetta 2 tank SVO conversion
1992 vw golf 2 tank SVO conversion
1998 2500 12 valve Cummins diesel with 2 tank SVO conversion
Making biodiesel in the back yard and running WVO in the vehicles with 2 tanks
 
Location: Burk's Falls, Ontario, Canada | Registered: July 05, 2003Reply With QuoteReport This Post
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I have a 92 first gen 12 valve Dodge Cummins, it has a mechanical diaphragm pump in the same place that yours has the piston pump. The diaphragm pumps output pressure is created by a spring, the engine cam lobe lever conpresses the spring only so if you deadhead the pump the spring just stays compressed and there is no damage to the pump. I suspect the piston pump works the same way but can not say that for sure, I am still looking for some sort of diagram of this pump to tell if it uses a spring for pressure, I strongly suspect that it does because they make a lower pressure version that can be used to replace my diaphragm type pump.

I used manual ball valves to select between tanks for a couple years, I simply dead headed the diaphragm pump and had no problems. I recently converted to two Mallory electric fuel pumps followed by low crack pressure hydraulic in-line chack valves to insure no backflow through the pump that is turned off, much nicer to simply flip a switch in the cab rather than stop and open the hood to change the mechanical ball valves.

My vehicle only applies 10-12 pounds pressure to the input of the rotary Bosh IP, yours need more pressure but I don't know just how much, someplace around 45 pounds I think, or maybe 28 pounds? I am using Mallory gearotor type pumps for both diesel and veg, the diesel pump is a model 4070 that is speced to move 70 G/H at free flow (no output pressure), this works fine for thin diesel but does not flow quite enough when pumping thick oil, I use a model 4110 Mallory pump for my veg, this is speced at 110 G/H free flow and has worked fine for either cold veg blends or heated veg. My IP returns about 2.5 times tha amount of fuel that the engine burns at highway speed back to the tank. At freeway speed the lift pump only needs to move something like 14 G/H, I suspect your IP moves more fuel back to the tank but not sure, I ran my return line to a seperate 5 gallon fuel can in the bed and ran the truck down the road for a measured time and then measured the amount of fuel in the return can. Mallory makes pumps with flows up to 250 G/H but you probably won't need anything larger than there model 4140 pump that moves 140 G/H, if that much

The mallory pumps can produce pressures up to at least 90 pounds, they have a built-in pressure bypass type pressure regulator that uses a spring behind a bypass piston to set the pressure, VERY easy to just change to a different spring to set what ever pressure you need. These pumps are less expensive even at full retail than the Fass or Airdog pumps, around $250.00 from a retail outlet but I buy them on Ebay for under $100.00 for both new or used, paid as little as $5.00 for the one I am now using for veg but had to put a $15.00 set of brushes in it, runs fine. These pumps move veg well once you remove the fine screen poked deep down inside there inlet fitting. They are also totally rebuildable and parts are available. The motors on the Mallory pumps can run warm, this does not seem to cause a problem But I found that by adding a 1 ohm 50 watt resistor in the 12 volt lead the motor runs a lot cooler but still has more than enough power to start and pump even very cold veg. I had to start on a 20 deg f 80% veg blend a couple times this last winter and the pump worked fine. Using the resistor puts 8-9 volts on the motor so it turns a bit slower, this is fine with thick veg, and less heat has to mean less wear-n-tare, pump runs very quiet also.

As of now I have left the diaphragm pump on the engine and the inlet to the pump and the outlet from the stock fuel filter open, the pump just moves air. I am using a seperate cheap Fram G-5 throw away in-line filter in the inlet of the electric diesel pump rather than the expensive stock fuel filter. I may just remove the stock mechanical pump as well as the stock fuel filter, the electric heater for the stock filter died years ago so there is no loss in doing this. I have a second Fram G-5 filter just before the IP, both veg snd diesel flow through it as a last ditch filter. I intend to add a 250 watt electric fuel heater just prior to this filter to help shorten my winter changover time from diesel to veg, this heater can possibly produce burnt veg crumbs that the last filter will catch.
 
Location: fisher,illinois,usa | Registered: June 03, 2003Reply With QuoteReport This Post
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Tim:
Thank you for the detailed reply. It's good to have a lead on electric fuel pumps that work on diesel/veg and have confirmation from a real world application saying they work. I'm not familliar with the mallory pumps, but will check into them. If they are reasonably priced I would get two, and then I'd be all set with one for diesel and one for veg. One nice thing about doing it that way is the VO Controller I plan to get has built into it a feature to activate either of two electric fuel pumps. So wiring it up shouldn't be too hard.

I think your first number regarding fuel pressure needed for my injection pump is right. They need approx 40 -45 PSI I believe. But if Mallory pumps are available that build the volumes/pressures you're talking about, then I should be able to get plenty for my truck.

I'll start searching for the right pump.

Thanks


1986 vw jetta 2 tank SVO conversion
1992 vw golf 2 tank SVO conversion
1998 2500 12 valve Cummins diesel with 2 tank SVO conversion
Making biodiesel in the back yard and running WVO in the vehicles with 2 tanks
 
Location: Burk's Falls, Ontario, Canada | Registered: July 05, 2003Reply With QuoteReport This Post
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I have been running a greasecar co-pilot for 4 years now with a looped veg return in Montana. I have never had a problem with the little bit of oil that goes back to the diesel tank. I purge for 45 seconds where diesel is pushed through the veg filter, heat exchanger and injection pump so I am diluting the veg before it goes back to the tank but am unsure how much. Years ago I was also concerned with this but not anymore. Not sure how many miles I have driven but must be at least 30,000 miles. I would stick with the stock lift pump, less to go wrong and to buy.
 
Registered: April 11, 2007Reply With QuoteReport This Post
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