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.