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Fuel Filter/Fuel Return?
by
Bugsy_malone 666
on 12 Jan, 2012 15:34
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Ok on my camper van I have just started on the process of fitting a Veg oil conversion (home built based on conventional designs) with twin fuel tanks(I have a second one to go in the back) a water heat exchanger to warm the oil and a change over valve, however there is one thing I am not sure about - Fuel return.
While the concept of a diesel is pretty simple, you have 2 connections to your fuel tank, one is a supply, which goes to a fuel filter, then the fuel pump, the other is a connetion for the return of excess fuel.
So thats easy, but I wondered, do you need to actually have the fuel return to the tank? I want to fit a different type of fuel filter for the veg oil tank (current diesel supply is just a stock 1 pipe in 1 pipe out vanagon filter) The type you find on tractors, where you have a filter head with a steel canister that bolts underneath, followed by glass bottom for monitoring water in the filter. With the tractor filter heads they have 4 ports on some of them, 2 in and 2 out or 1 out and 3 in (cant rememeber without looking at one).
So the question is rather than weld a return to my second fuel tank, could I just have the fuel return go to one of the inputs on the fuel filter itself?
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#1
by
burn_your_money
on 12 Jan, 2012 19:35
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Yes, and it's probably a good idea to do it because it will be hot fuel that won't need to be heated again. Plus, it will help to prevent the filter from gelling.
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#2
by
81 vw pu
on 13 Jan, 2012 01:23
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The only problem with a looped return is if you get an air leak. (no where for air to escape)
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#3
by
Bugsy_malone 666
on 13 Jan, 2012 06:18
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The only problem with a looped return is if you get an air leak. (no where for air to escape)
I am wondering if this would really pose much of a problem? As I don't think the vw diesel is auto bleed so any air on the supply side would cause a problem any way just leaving the return side which I am wondering why I'd get an air leak in the first place? Maybe I am missing a trick? Although I do see your point.
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#4
by
mtrans
on 13 Jan, 2012 15:05
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With a looped return I add el.valve to tank, for air and if I think it`s too hoot.Right now I change rest of my 4 el.valve with two 3-way manuel ball valve,so only 1 on return stay.
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#5
by
the caveman
on 14 Jan, 2012 13:06
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I have had much less success with looped returns than with a fuel return to the tank. The suggested purpose is to keep the returned warm fuel[i.e. VO] recirculating. However returning the warm fuel to the VO tank means the VO in the tank gets warmed and therefore heating the whole system from the beginning. Also if you get air in the loop from running out of fuel, it's a pain to bleed it out. And lastly, most looped systems need 3 valves instead of 2
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#6
by
Bugsy_malone 666
on 14 Jan, 2012 16:04
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The bit I dont get is about the valves? 3 rather than 2? I am sure I have missed something here.
I think primarily I dont really want to have to run a second long return line back to the tank, meaning less piping and only out going from the cabin to the engine bay.
Heating the VO isnt a problem, I have a decent heat exchanger for that which will be located in the engine bay. Its only the VO system that wont have a retun on it, the diesel tank currently has a return line to it. I dont plan on running out of veg oil, as when its low I will switch back to diesel and the diesel has the return anyway. I suppose in some respects its short cutting, but at the same time the tractor filters seem to have a return line to them (infact most have several in and several out) and I just figured that maybe the way forward.
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#7
by
williamtaygan
on 14 Jan, 2012 16:06
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I did a little write up about this a while back:
http://vegwerks.wordpress.com/2008/01/16/the-best-svo-fuel-line-routing-design/Most vendors are going to a 3-valve controlled loop: The third valve switches the veg return from a loop while running (I like to loop after the filter), and a return to tank while purging.
Personally, my next conversion (1.6NA Westy - warm garage scheduled for next week.) will have a running loop return after the filter and before the Flat Plate, and a purge loop backflushing right before the valve - priming the veg line with a diesel-veg blend. This wastes a little diesel on purge, but thins out the unheated valve for extreme cold temps (I'm in Alaska).
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#8
by
Bugsy_malone 666
on 14 Jan, 2012 17:02
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ok for the VO setup I actually have this:
A 6 port pollak valve 2 tank supplies, 2 tank returns and one engine supply/return, so it just switches straight from one to the other.
The plan was going to be connection from VO fuel tank to a primer bulb(the type you find on boats, I have one on the diesel line and it works brilliant), to filter head (4 port design), filter head to the heat exchanger, heat exchanger to the pollak 6 port valve, then return from the pollak valve would go straight back to the filter head (on the inlet side).
The diesel loop goes from the tank, primer bulb, then filter and will then go to the pollak 6 port, the return from the 6 port goes straight back to tank.
I start the van on diesel, get it up to 50c then switch over. I was thinking of 50c, because the glow plug inhibitor switch on the head stops the glow plugs coming on at 50c so I could use a relay to power the valve over to VO automatically when it reaches the right temperature, then just switch back and count to about 40 should probably purge the system enough before switch off.
Maybe I am still missing the valve setup or mines just different?
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#9
by
williamtaygan
on 15 Jan, 2012 12:42
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First of all, I'm assuming you've got a fuel leak in your injection pump or somewhere, otherwise you wouldn't need the primer bulb.
I've done a few veg systems with a Pollak valves. I would only use them in warmer weather (above 5c), since there's no purge cycle. When you switch things off all the veg in the lines between the supply valve and the through the injection pump and back to the return is all sent directly to your diesel tank. If you add a separate valve for return you can keep burning up veg, purge the system, and then turn off the return valve 30 seconds later when the lines are clear of veg so you're not contaminating the diesel tank. IF it's always above freezing, and you don't switch back and forth a lot you'll probably be fine with your current setup.
I would loop after the filter and before the heat exchanger - There's less draw on a semi-plugged filter so it's easier on your system, and it doesn't re-filter the oil, possible extending filter life.
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#10
by
Bugsy_malone 666
on 15 Jan, 2012 13:17
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I dont have a leak on my injector pump, the primer bulb is just before the fuel filter so I can reprime the filter when I change it.
In the UK I think theres only about 2 months a year where it actually gets below 5c and generally speaking I dont use the van during those 2, however my long term plan revolves around potentially making the van my 12 months a year vehicle!
Today I have been looking at my second fuel tank and I am looking into just putting a return in the top, so its a complete loop like the diesel system, however I need to do a lot of work to fit the tank first then work out what sort of return fitting to fit.
It just seems easier by all accounts.
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#11
by
williamtaygan
on 15 Jan, 2012 23:57
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Just adding a loop won't help with the slug of oil going to the diesel tank. I generally DON'T return to tank (I've done about a dozen Alaska-hardy conversions), but I do use a second valve so I can delay the return switch until the veg is out of the system.
My current conversion is using 2 of those old-style motorized 6-port pollak valves in a 3-valve configuration. Sure the pollaks are plastic and won't hold up to real high temps, but I'm salvaging parts and have a couple lying around. We'll see how it goes!
Good Luck!
Will.