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Second Fuel pump for twin tank system?

 
 
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cieranc
Just got MTs


Joined: 20 Mar 2005
Odometer: 451
Location: Darlington



PostPosted: Thu Dec 20, 2007 2:01 pm    Post subject: Second Fuel pump for twin tank system? Reply with quote

So I'm fairly happy with how my 200TDi 110 is running on a blend of SVO/Petrol/Diesel, but I'm concerned about possible damage on cold starts. After compounding advice, twin tank is the way to go.

Currently, my fuel flows from the existing tank, to the lift pump, to a FPHE, to the heated filter head, to the injector pump. The return is direct to tank. I intend to use this original system as the secondary system for oil.

When I add the second, smaller tank for diesel though, will I have to add an additional pump for the diesel? Is there enough pull from the IP if I simply add a Peugeot/Citroen type priming bulb?
If I use the original lift pump for diesel, is there enough pull from the IP to pump the oil from the main tank, or will I need a pump there? How will the system be primed and bled without a lift pump, and will it suffer airlocks?

Everything else seems straight forward, one 3 way valve close to the IP, tee the returns back into the feed pipes before the valve and add a temp. gauge more accurate than the vague LR one.

Would this system work:

Advice please guys!
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Nathaniel
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Joined: 13 May 2003
Odometer: 17901
Location: North, North Yorkshire


1979 Suzuki LJ

PostPosted: Thu Dec 20, 2007 3:04 pm    Post subject: Reply with quote

Really you want another 3 way valve because when you switch back to diesel it'll take about 5 miles to purge the system, Loop the Veg return but send the diesel return back to the tank.

Your diagram plan is just fine except I would swap the position of the filter and heat exchanger.

You don't need a heated filter - but I like mine and improves matters if its REALLY cold!

I got a lot of bits from here

http://www.biotuning.co.uk/ShopHeatExchangers.htm

My heated filter is the same one that is on that website however mine cost £10 from a scrapyard and cleaned up nicely in the Ultrasonic bath at work!

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Nat

If You Open Your Mind Too Much Your Brain Will Fall Out
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Nathaniel
Difflock Royalty


Joined: 13 May 2003
Odometer: 17901
Location: North, North Yorkshire


1979 Suzuki LJ

PostPosted: Thu Dec 20, 2007 3:08 pm    Post subject: Reply with quote

Also have a look on here for ideas

http://www.vegetableoildiesel.co.uk/forum/index.php

You're most welcome to pop and see me and have a look over my conversion at some point.

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Nat

If You Open Your Mind Too Much Your Brain Will Fall Out
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The Smiths
Articulating


Joined: 21 Nov 2007
Odometer: 711
Location: Doncaster



PostPosted: Thu Dec 20, 2007 3:20 pm    Post subject: Reply with quote

You could also use just one main filter after the valve with no need to heat it - will take longer to change over though as you need to empty the filter - but then again not a big jump between the two as the ratio will change gradually.
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If you always do what you have always done,
you always get what you've always got.
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cieranc
Just got MTs


Joined: 20 Mar 2005
Odometer: 451
Location: Darlington



PostPosted: Thu Dec 20, 2007 5:21 pm    Post subject: Reply with quote

Thanks for the advice guys, a few further questions though Pray :

Why would it take around 5 miles to purge the system, the mixed fuels would only be held in the system between the 3 way valve and the IP?

Would the 3 way switches (Tecalemit type) require a relay to operate them, or is their required current low enough to feed them direct from the cab switch?

Would piping the IP return back to the tank when switched to diesel contaminate the diesel tank with SVO?

Cheers again
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Nathaniel
Difflock Royalty


Joined: 13 May 2003
Odometer: 17901
Location: North, North Yorkshire


1979 Suzuki LJ

PostPosted: Mon Dec 24, 2007 11:44 am    Post subject: Reply with quote

cieranc wrote:
Thanks for the advice guys, a few further questions though Pray :

Why would it take around 5 miles to purge the system, the mixed fuels would only be held in the system between the 3 way valve and the IP?


Because the fuel just goes around the loop and only takes the small amount that is actually used.
A return line actually returns 10 times more fuel than is actually used, so when purging it would quickly flush the IP with diesel.

Quote:

Would the 3 way switches (Tecalemit type) require a relay to operate them, or is their required current low enough to feed them direct from the cab switch?


No, they won't need a relay.

Quote:

Would piping the IP return back to the tank when switched to diesel contaminate the diesel tank with SVO?


Yes but not enough to matter. Hardly any at all.

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Nat

If You Open Your Mind Too Much Your Brain Will Fall Out
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cieranc
Just got MTs


Joined: 20 Mar 2005
Odometer: 451
Location: Darlington



PostPosted: Sat Dec 29, 2007 10:32 pm    Post subject: Reply with quote

Thanks Nat, I've got this clear in my head now what needs doing.
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