how many valves needed for no diesel/vo contact? - PeachParts Mercedes-Benz Forum

petecooke · #1 08-13-2015, 07:51 AM

I have a 1984 300d and was wondering what the best wvo setup would be to not put wvo back into the diesel tank.

I've seen many wvo diagrams that show the following
wvo tank >3 way valve>lift pump>3 way valve>wvo filter>FPHE>TEE>injectors>3 way valve>wvo tank

diesel tank >3 way valve>primary filter>lift pump>3 way valve>secondary diesel filter>TEE>injectors>3 way valve>diesel tank

The banjo bolt would be blocked.

Would it make sense to replace the TEE with another 3 way valve so when running diesel there would be no bleeding of wvo from the WVO filter and FPHE?

This would require four 3 way valves.

I would also think a delayed return, when switching to diesel, would be a good idea so the injection pump would purge the wvo in the injection pump back to the veggie tank before returning the diesel fuel to the diesel tank.

Any thoughts?

Thx

pete

Simpler=Better · #2 08-13-2015, 10:16 AM

You're overthinking it. Two three way valves is all you need. You'll end up heating some diesel while warming up, and dumping some diesel into the WVO tank during cooldown, but it's the easiest way to do it.

Also, I've got my cheapo 3way plastic valves somewhere in my shed. They're yours for cheap if you want em'

petecooke · #3 08-13-2015, 11:06 AM

Are you putting the first 3 way valve after the lift pump and bypassing the lift with your wvo?

Is this your setup?
wvo tank >3 way valve>filter>FPHE>TEE>injectors>3 way valve>wvo tank

diesel tank >3 way valve>primary filter>lift pump>3 way valve>secondary diesel filter>TEE>injectors>3 way valve>diesel tank

Thx

pc

AcIdBuRn · #4 08-13-2015, 11:12 AM

Why not loop the return and run 1 valve?

petecooke · #5 08-13-2015, 11:15 AM

I've heard issues with bleeding air when changing filters.
Sending it back to the tank isn't a big deal since it will be a HIH and there's coolant going back to the trunk anyway.

pete

AcIdBuRn · #6 08-13-2015, 11:21 AM

Haven't had any issues yet thus far with bleeding air.

Anyways... if you do a return system, you'll need 2 3 port valves... just switch them independently to keep contamination to a minimum.

moon161 · #7 08-13-2015, 01:15 PM

(2) 3 way valves will work. With a delay on one of the valves you can flush the system to prevent WVO or WMO from getting in your diesel tank.

I can find a sketch I made and post it.

petecooke · #8 08-13-2015, 02:40 PM

Are you using the secondary fuel filter with the wvo?

Are you using the lift pump with the wvo?

How is the wvo flowing with only two 3-way valves?

Thanks.

pete

ah-kay · #9 08-13-2015, 02:50 PM

Quote:

Originally Posted by petecooke

Are you using the secondary fuel filter with the wvo?

Are you using the lift pump with the wvo?

How is the wvo flowing with only two 3-way valves?

Thanks.

pete

Most if not all system uses the secondary fuel filter and the lift pump with WVO or diesel. They are singleton in the car. You have 1 feed line and 1 return line so you only need 2 x 3-way valves. One at the feed and one at the return line. WVO and diesel will mix during switching, within IP at least even if you add separate electric lift pump. There is no way you can prevent it.

AcIdBuRn · #10 08-13-2015, 02:54 PM

Supply 3 port valve...

1 feed port - WO tank

1 feed port - diesel tank

1 common port (outlet) - lift pump supply port

Return 3 port valve

1 common port (inlet) - filter head return

1 - outlet - wo tank

1 - outlet - diesel tank

Single filter.. single pump.

When switching fuels, switch the return first, then supply (when going from pump fuel to wo)... when going back to pump fuel, switch the supply first... wait a few then switch the return. That way you wont have any wo mixing with the diesel tank... might get a little diesel in the wo though.

OOOrrr...

Loop the return. 1 valve and no mixing of fuels.

petecooke · #11 08-13-2015, 03:30 PM

Thanks guys for the info.
I'd like to buy some translucent silicone line so I can actually see the fuel switch and better track down problems when they occur.

I've see some clear pvc fuel line but I know it gets hard when exposed to heat for a long period of time.

My only concern about using the secondary diesel filter is it clogging if the wvo has to much fat in it. I like the idea of having a completely parallel system to be able to automatically switch to when problems arise.

I may test both. I have 2 cars I want to convert so the extra valves won't go to waste.

Thanks again.

Pete

GregMN · #12 08-14-2015, 07:58 AM

1991 350 SDL Conversion to WVO

petecooke · #13 08-14-2015, 08:39 AM

Thanks Greg for the link. I've never seen a setup like that. I'm not sure why he is heating the diesel fuel. Also, after the lift pump, he doesn't list the diesel or wvo to to the secondary fuel filter. You can see the secondary fuel filter in the engine compartment so both fuels must be going to it. I've read that you want the fphe right before the injectors but, in his sub-zero climate, maybe the trunk is better. I like getting the heated fuel filter and fphe out of the engine compartment but the loss of heat could be a problem as the fuel travels to the engine and changing filters could be a mess in your trunk. Original diesel fuel flow: tank > inline filter > fuel heater > lift pump > diesel filter > injection pump. Returned fuel from the injection pump, injectors, and diesel filter all meet at the banjo bolt fitting on the diesel filter body then to the return to tank line. Modified diesel fuel flow: tank > inline filter > fuel heater > diesel filter > fuel selector valve > lift pump > injection pump. VO flow: tank > short heat exchanger > flat plate heat exchanger > heated fuel filter > hose in hose fuel line > fuel selector valve > lift pump > injection pump. pete

GregMN · #14 08-14-2015, 10:53 AM

The max. temp. the VO can get to, using coolant for heat, is the temp. of the coolant. It cannot get any hotter. It doesn't matter if it reaches that temp. in the trunk, or in the engine compartment. The 13' of copper tube inside the 3/4" coolant hose keeps the VO at the coolant temp. on it's trip from the trunk to the engine. There is no loss of heat.

I cut the bottom off of a gallon plastic bottle and put that under the filter when I change filters to catch the drips. No matter how careful you are, you are going to spill VO in that fender-well some day. When that happens, pull the drain plug on the fender-well, spray it down with degreaser, pour a couple of buckets of hot water in there and let it all drain out and dry out. If that is the worst mess you ever make with VO, you are lucky. This is a messy business.

oldsinner111 · #15 08-16-2015, 12:07 PM

when I did mine I used a NAPA filter head with 5 micron cartridge.It had 2 inputs,and 2 outputs.I blocked off one output,ran from other output to heat exchanger,then into lift pump.I disconnected cigar hose and used a shut off valve with a three way,and ran hose back to other filter input.This way I could loop my fuel.I had a 2 way common garden hose valve that conncted to either veg tank,or diesel tank.I ran short hose into a 12 psi electric fuel pump to push either fuel to engine.Thiis took care of bleeding problems.I would switch back to diesel for a few miles when parking over night.