purge is nothing more than what I call my return line solenoid. It in effect purges any air in the line back to the diesel tank. for instance:
Say I decide to switch over to veggy. I throw both the veg and loop (purge) solenoid switches. Now I feel the truck starting to struggle. Possible air in line. What I do is shut off the "purge" switch and all return fuel, including vegy goes to the diesel tank. Once I smooth out, I flip the switch and I am back in a loop mode. problem solved.
Shutdown:
When I am a few miles from my house ,I throw the Veg switch off switching back to diesel but I leave the return(purge) switch activated. The return fuel has no where to go but back up the veg line backwashing the filters with is now a diesel/vegy mix. A little hard to explain without a picture diagram. The next morning I can switch over sooner because the filters in the vegy system are really full of about 80% diesel.
The last three days here on Long Island its ben 70 during the day and 50 at night. I have not been flushing the system before shutdown as a test and the truck starts instantly on cold vegy each morning . Amazing!!!
By the way, The grease I got is from a chineese food restaurant and boy my exhaust smells good...... Mike