Looped Return question

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Looped Return question

Postby Karma50 » Tue Jul 29, 2008 6:37 am

New to the forum. I am currently installing a 2-tank conversion in my '85 Mercedes 300D. But I need some tips on the purge return. Here is my schematic so far:

<img src="http://i44.photobucket.com/albums/f42/Karma50/WVO-Schematic.jpg" border="0" alt="300D WVO Schematic">

Can anyone provide me more input on how to set up the VO return? Am I connecting it in the right part of the fuel line? I have seen other schematics that seem to prefer running it through the filter again? Is this necessary? How can I do this with a two filter system? (Obviously during purge I will be running the return through the loop but I would be pulling from the diesel tank/filter).

Do I need any check valves to make sure the flow is going the right direction in the area where I run the looped return?

Can anyone shed any light on how to get air out of the VO looped return. I have been reading about doing a limited loop return with a needle valve (which is shown with this schematic) but I really don't know how to do it. Is anyone else using a similar looped system? How do you make sure air doesn't get trapped?

I appreciate any help! :)
1985 Mercedes 300D 425k miles (installing a 2-tank WVO system)
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Postby SunWizard » Tue Jul 29, 2008 6:58 am

Welcome to the forums. Nice diagram. But you need to put your lift pump on there, which complicates things since its before the stock filter, you can't do it as you show.

You could see my Dodge Cummins thread under converted vehicles here, its almost the same as Mercedes. I have never had trouble with air in my lines, but each time I switch to D2 it is return to tank, so I would switch to D2 for a few minutes if I did get any air, like after a filter change.
YVORMV - Your veg. oil results may vary.
95 Dodge Cummins 4x4 SVO WVO conversion.
81 Mercedes 300D- stock and happy on V80/D20 blend.
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Postby hheynow » Tue Jul 29, 2008 10:24 am

To over simplify the return, the vegoil return enters a "tee" which feed it to the vegoil filter along with the vegoil from the tank.
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1984 Mercedes Euro 300D NA - Custom two tank
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Postby Karma50 » Wed Jul 30, 2008 4:47 pm

SunWizard wrote:you need to put your lift pump on there, which complicates things since its before the stock filter, you can't do it as you show.


Are you sure? I thought the lift pump was a part of the IP in the case of 617 Mercedes engines. Granted I do not know alot about this yet but I am learning. Can anyone please shed some light on this for me. Is the lift pump a part of the manual primer pump? As far as I can see that is the only thing in the fuel line between the firewall and the IP. Is it under the car closer to the tank?

If there is a lift pump before the filter, how should I change my schematic? I understand it is bad to run the mechanical pumps when nothing is flowing through them. How do I circumvent this? Do I tie the electrical connections for the lift pump to my switch?
1985 Mercedes 300D 425k miles (installing a 2-tank WVO system)
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Location: Dallas, TX

Postby Karma50 » Wed Jul 30, 2008 4:53 pm

hheynow wrote:To over simplify the return, the vegoil return enters a "tee" which feed it to the vegoil filter along with the vegoil from the tank.


If I did this how would I purge the VO before shut-down? Isn't the point of the VO return to allow for a purge: selecting fuel source from the diesel tank and looping the return until the VO is used up and it is only diesel left then sending the return back to the diesel tank for start up. If I looped the VO return before the filter as I have the set up now would make purging impossible. Should I move the switch to before the filters and use both of the filters for both fuel in series, this would also solve the lift pump issue if the lift pump is in fact a part of the manual primer pump.
1985 Mercedes 300D 425k miles (installing a 2-tank WVO system)
Karma50
 
Posts: 6
Joined: Mon Jul 28, 2008 7:51 pm
Location: Dallas, TX

Postby Karma50 » Wed Jul 30, 2008 5:11 pm

Sorry to posts 3 separate replies in a row but I just went and took a picture of my fuel system as best I could.

Image
1985 Mercedes 300D 425k miles (installing a 2-tank WVO system)
Karma50
 
Posts: 6
Joined: Mon Jul 28, 2008 7:51 pm
Location: Dallas, TX

Postby SunWizard » Wed Jul 30, 2008 7:24 pm

Karma50 wrote:
SunWizard wrote:you need to put your lift pump on there, which complicates things since its before the stock filter, you can't do it as you show.


Are you sure? I thought the lift pump was a part of the IP in the case of 617 Mercedes engines. Granted I do not know alot about this yet but I am learning. Can anyone please shed some light on this for me. Is the lift pump a part of the manual primer pump? As far as I can see that is the only thing in the fuel line between the firewall and the IP. Is it under the car closer to the tank?

If there is a lift pump before the filter, how should I change my schematic? I understand it is bad to run the mechanical pumps when nothing is flowing through them. How do I circumvent this? Do I tie the electrical connections for the lift pump to my switch?

Yes I am positive, I have a 617 engine on my Mercedes. The lift pump is mechanical which is the best type, and attached to the primer pump. I prefer the diagram on my Dodge Cummins thread under converted vehicles here, its almost the same as Mercedes. Here it is again:
Image

Also you can't have the return attached to the top of your stock filter, or when running on VO it will return some VO to the D2 tank.
Last edited by SunWizard on Mon Sep 20, 2010 8:54 pm, edited 1 time in total.
YVORMV - Your veg. oil results may vary.
95 Dodge Cummins 4x4 SVO WVO conversion.
81 Mercedes 300D- stock and happy on V80/D20 blend.
Low fossil net zero house- 100% solar power and heat.
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Postby Karma50 » Wed Jul 30, 2008 9:40 pm

I would rather not have 2 switches on the fuel side (3 total) for simplicity sake (and because I already have 2 HydraForce Solenoid valves and I don't want to have to order another one). This appears to leave me with two options:

1. Switch the stock path of fuel from:
Lift Pump -> Filter -> IP
to:
(Diesel or VO) Filter -> Switch -> Lift Pump -> IP

2. Use both filters in series:
VO Tank -> FPHE ->
- - - - - - - - - - - - - - Switch -> Racor Filter -> Lift Pump -> Stock Filter -> IP
Diesel Tank ------->


Is putting the lift pump just before the IP okay? I assume the stock filter prefers pushing fuel rather than pulling it through. (Pulling fuel is what my Racor filter used for VO recommends.) Would it work anyway?

For those of you that know more about the mechanics of this fuel system than I, which do you think is better? Is there another, better option? What are the upsides, downsides of both?

I guess I could also add an additional lift pump to the VO side. But I would prefer to avoid this set-up considering that I would be adding a lift pump that the IP was not designed for. I would also have to figure out how to turn off the lift pump that is not being used.

P.S. To avoid mixing fuels in the top of the diesel filter I am replacing the ported banjo bolt with a solid one.
1985 Mercedes 300D 425k miles (installing a 2-tank WVO system)
Karma50
 
Posts: 6
Joined: Mon Jul 28, 2008 7:51 pm
Location: Dallas, TX

Postby SunWizard » Wed Jul 30, 2008 10:59 pm

Option 1 is better, but the stock filter isn't designed for vacuum. Your purge time would be awful with option 2. When under vacuum you are much more likely to get air leaks, and the filters don't last as long. Pumps are much more effective pushing than pulling. This is why I designed for pressure, same as the best stock setups.
YVORMV - Your veg. oil results may vary.
95 Dodge Cummins 4x4 SVO WVO conversion.
81 Mercedes 300D- stock and happy on V80/D20 blend.
Low fossil net zero house- 100% solar power and heat.
SunWizard
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What computerprogram...

Postby sm7bxd » Thu Jul 31, 2008 11:05 am

...did you use to make that nice presentation?

/sm7bxd
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Postby Karma50 » Fri Aug 01, 2008 2:44 am

I used Adobe Illustrator. I work with Photoshop professionally. It might be a little too much for doing this kind of thing.

Here is my adapted schematic:

Image

I am going to take SunWizard's advise and just go straight from the Lift Pump (Primer Pump) into the IP. It also appears to be what Frybrid recommends for Mercedes conversions.

Thank you SO much for all the help! I really appreciate you all going over my setup and giving me advice from your own conversions. This is what community is all about! I will post results once I get it done.
1985 Mercedes 300D 425k miles (installing a 2-tank WVO system)
Karma50
 
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Joined: Mon Jul 28, 2008 7:51 pm
Location: Dallas, TX


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