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  #1  
Old 03-01-2005, 05:05 PM
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SVO/WVO system: looped vs. return lines

In _From the fryer to the fuel tank_ the author recommends a system that he claims eliminates the need for return lines by looping the return line from the IP.

What are people's feelings about this? Most of the other systems I've seen here and elsewhere use either a 6 port solenoid or a second 3port solenoid to return diesel and WVO to their respective tanks.

What are the advantages/disadvantages of either system?
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  #2  
Old 03-01-2005, 05:10 PM
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mostly I have heard (from dana) that it is best to loop the return of the veggie, while returning diesel to its tank as usual.

Check out the svo/wvo forums over at http://biodiesel.infopop.cc/eve/ubb.x/a/frm/f/159605551

Loads of good info, and Dana is there to help!
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  #3  
Old 03-01-2005, 05:35 PM
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In the first SVO systme I built, looping was easy because I used the lift pump for both fuels; it also kept the heat in the oil.

In the system I'm building now, I have a separate pump for the oil, and I'm reluctant to loop the return because I need to bleed the air out. Since I'll have a small SVO tank, I'm just going to return excess oil to the tank and heat the whole tank as I go.
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Old 03-01-2005, 06:12 PM
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Also, if you run a single tank system with blends, the return line helps to heat up the main fuel tank, easing the flow of oil. I'm using a coolant/fuel heater with a 12-volt Dana special in-line fuel heater. I'm going to add a 110 volt water heater element to my fuel tank for morning plug-in to get the tank warm before I'm going. A little HOH and I should be good to go with 80-90% WVO!
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  #5  
Old 03-01-2005, 06:41 PM
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I have always thought that running a return line made the most sense. The arguement is that a looped system retains the heat better. If you are running the WVO through a large enough coolant heater it will be at coolant temp when it comes out so what difference would looping make? The benefits of returning the WVO to the tank are quicker heating of the WVO tank and easier flow so its easier on the pump, etc. I can't imagine its a good thing if you are running an additional electric lift pump to have it deadhead into the looped system either. Lastly, the return system allows the fuel delivery system to operate as the designers intended. No need to plug up certain bolts, automatic bleeding of air in the system, etc. The only possible negative I can see is that on long trips in the summer the WVO tank may get pretty hot. If this is the case it may be a simple solution to instal a valve to shut down coolant flow to the in-tank coolant heater/HOH lines and just use the underhood coolant heater to get the WVO to temp. This way it would take a lot longer for the returning WVO to heat up the entire tank yet the WVO would still flow reasonably well at summer temps. Lastly, heres a cool WVO filter http://www.davcotec.com/model234.htm Wow, long post, sorry. RT
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  #6  
Old 03-01-2005, 07:07 PM
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I have been giving this topic a lot of thought. It seems to me that there are a lot of short comings from both the greasecar.com (returned) and the greasel.com (looped) kit.
One of the things I have been trying to come up with a better design for is the looped / returned line topic you have asked about.

The looped design is the best overall because if you donít loop the line then you have to purge the WVO out of the return line with diesel. If you donít you risk the WVO solidifying and clogging the lines. This is an eventual problem in the works.

What I like about the looped system is the quickness of the purge. If you have the 3 way valve as close to the IP as possible all you have to do is purge the WVO out of that inch or two of line and what is left in the IP.

Now what I am thinking is the absolute best way to do this is to have 2 x 3-way valves and a combination of the return and looped system.

My reasoning for keeping the return line is a quicker heat up time for the WVO tank and more highly filtered WVO.
I figure if you have it setup where the WVO has a heated supply and return lines it will constantly pump heated WVO back to the fuel tank. This should cut down on tank heating time. Also the fuel will have passed through the filter several times instead of just one time like in the looped system. This is especially useful if you are using a water separator.

The other 3-way valve would be to switch the return line (from the IP) to a loop when running on diesel. This way you still get your quick purge.

I hope this makes since.
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Old 03-01-2005, 11:44 PM
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That book, "From the Fryer to the Fuel Tank," is great nostalgia, but old, old news. Veg oil systems have come a long way since then. Check out the great diagrams on the infopop board...
Looped returns cut down on amp draw, if you are pre-heating electrically. The most important thing, imho, is the oil temp when it hits the IP. Tank warming takes a back seat to that, and coolant is a superior way to do that.
I'm gonna loop the return, with the solonoid, so I am never looping hot diesel.
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  #8  
Old 03-02-2005, 12:42 AM
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.02

From what I gather the biggest advantage to looped fuel return is not heat of oil being thinner fuel for better automization of veg oil pumped into the cylinder/prechamber as much is it is reducing the strain on the IP. The IP does "pull" fuel to some extent as well as pressurize it (push fuel). Some IP's pull fuel more than others such as my Nissan LD28 that has NO FUEL PUMP except the IP itself. Anyway looping the return means thiner oil (closer to viscosity of diesel) is being pulled/pushed by the IP thus keeping the IP opperating under circustances closer to OEM standards. Yea it is hotter but the viscosity is more tolerable. Besides it has been said that hot veg oil acutally cools the IP as good or better than normal operating temp diesel. Thats due to properties of vegoil.

SIDE NOTE: It is not hard to bleed air from a fuel return loop by adding into your return loop a gas car; air bleading, inline fuel filter. These filters are for cars that were found to have vapor lock issues with out such a device. Check you local Cheapo auto part store for inline fuel filters that have 3 ports. The third one you would attached to the return fuel line to the tank. These little buggers bleeds air and a little fuel. I assume you pick the filter shape that when mounted will put the air bleed port as verticle as you can get it. I say this cause the way I assume these filters work is the air in the filter travels upwards vertically. Anotherwords the fuel is usually pushed out horizontaly while the air (and a little fuel) exits vertically.
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  #9  
Old 03-02-2005, 01:02 AM
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right on. the hotter the oil, the lower the viscosity; you want it as low as possible to mimic that of diesels viscosity-for a number of reasons.....and those are two good ones.
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Old 03-02-2005, 11:05 AM
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How hot does the oil need to be? All my research indicates that 160*-180* is optimal. This is slightly lower than coolant temp in most engines. So if you are running a coolant heat exchanger to heat the WVO and the WVO temp leaving the heat exchanger is at least 160* (likely it will be hotter) right before it hits the IP why would running a loop have any benefit? The "WVO solidifying and clogging the lines" in the return system is not a problem. If you are running the simplest HOH system you already have two coolant hoses, a feed and a return to heat the tank and the WVO feed line. Adding a second WVO return line to the HOH bundle will keep the WVO from solidifying and also add its heat to the bundle of hoses to heat up the WVO feed line. Simple. RT
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  #11  
Old 03-02-2005, 09:25 PM
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Your point is valid. There is not much difference between my suggestion and yours. Basically it comes down to preference between running a looped system for diesel return or running another heated line for WVO return.
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