check/bypass valve... need ideas

[notfarnow]

I'm kinda stumped, and I figured that the PPOT brain trust would surely have some suggestions.

I'm getting started on the vegetable oil conversion for my '99 e300d. The basic principle is that the car starts on diesel, then once it's warmed up I switch to vegetable oil. Before I shut the car off, I switch back to diesel.

This requires switching both the supply line and the return line. In the past, I've used a single 6 port valve to accomplish this. On this conversion, I'll be using 2 3-port valves.

Now, by using 2 3-port switching valves, I am able to set up an "in between" purge cycle. This ensures no vegetable oil is sent back to the diesel tank, and it also backflushes the veggie filter and means when you start on vegetable oil the next time, you'll actually be starting on a veggie/diesel mix.


(IP=injection pump, V=valve, F=filter, FPHE=flat plate heat exchanger)

Problem is this:
In order to "purge" backwards through the veggie system, I need a way to bypass the electric fuel pump for the vegetable oil. Most people use a third 3-port valve (~$135 each) for this. I'd like to keep it a bit simpler by using a check/bypass valve.

Here's a fancy MS Paint drawing of what I'm trying to accomplish:


Anyone know of any reliable bypass/check valve that could redirect the flow? Need about 1/2" internal passages and capable of ~12psi.

[craigster59]

Did you try www.mcmaster.com ? They might have something you can "McGyver" together. Good luck.

[notfarnow]

Originally Posted by craigster59

Did you try www.mcmaster.com ? They might have something you can "McGyver" together. Good luck.

Yep, and I haven't found anything that seems to work this way. Mind you, I'm not sure I know what to look for either.

I'm doing my best to not "McGyver" too much on this conversion. In my Jetta, I "McGyvered" a float switch in the fuel tank, to shut off the pump when I was filling it up.

Worked great the first 10-15 times... just enough to get comfortable walking away from it while pumping. Then one day it pumped ~130 liters. Tank only held 55.

It wasn't pretty.

[Porsche_monkey]

Buy a hydraulic flow control (Parker) and close off the flow adjuster. They have a built in ball check and are made for use in oil.

[Porsche_monkey]

Or McMaster Carr Part No. 7775K11

Or go to plumbing outlet and ask for a cast brass check valve for water circuits. Should be about $15 each and the mount vertically (gravity close) 1/2NPT.

[NICKG]

can you use a nos fuel solenoid?
they must make an industrial version..i would agree on mcmaster carr
maybe even grainger

[turbo6bar]

Could you place two check valves in there? One would be at the fuel pump. Another would be in the bypass line. This check valve (in the bypass line) would have cracking pressure higher than the rated pressure of the fuel pump.

You could avoid this mess by making biodiesel. Then again, I am a silly bed wetter.

[notfarnow]

Originally Posted by PBH

Buy a hydraulic flow control (Parker) and close off the flow adjuster. They have a built in ball check and are made for use in oil.

Originally Posted by PBH

Or McMaster Carr Part No. 7775K11

Or go to plumbing outlet and ask for a cast brass check valve for water circuits. Should be about $15 each and the mount vertically (gravity close) 1/2NPT.

Would either of those divert the backflow around the fuel pump?

Originally Posted by NICKG

can you use a nos fuel solenoid?
they must make an industrial version..i would agree on mcmaster carr
maybe even grainger

If I get into solenoids, I'd just use a 3rd 3-port valve. I'd trying to cut down on the wiring & switching by going with something that will just divert the flow when it backflushes.

Originally Posted by turbo6bar

Could you place two check valves in there? One would be at the fuel pump. Another would be in the bypass line. This check valve (in the bypass line) would have cracking pressure higher than the rated pressure of the fuel pump.

You could avoid this mess by making biodiesel. Then again, I am a silly bed wetter.

Exactly... Biodiesel is for bed wetters! Seriously, I'm not quite sure I have my head around your concept. Part of the problem is I've never used a check valve, so I'm not entirely sure what I should be looking for.

[turbo6bar]

Originally Posted by notfarnow

Exactly... Biodiesel is for bed wetters! Seriously, I'm not quite sure I have my head around your concept. Part of the problem is I've never used a check valve, so I'm not entirely sure what I should be looking for.

When you're running on WVO, the check valve in the bypass line stays closed. When you backflush with diesel, the check valve at the FP closes, and the check valve in the bypass line opens. In order for this to work, the pressure of the backflush diesel must be higher than the pressure from the veggie FP.

I don't know if a check valve with bypass even exists.

[notfarnow]

Thanks Turbo6bar, that makes sense now.

Turns out things are more complicated than I anticipated. The fuel pump I'll be using has a regulator with bypass.