I'm converting my '82 E350 van to propane (only, not dual-fuel).
See my gallery for specs on the van and motor, if interested.

I've acquired the mixer, vaporizer & lockoff (Impco 425, Model E & VFF30) as well as a 20 gal tank to replace the rear gas tank under the back of my van (13" + 10" x 30" welded together -- a manifold tank, they call it).

This should get me up and running on the gas, but down the road, I'll want to replace the other gasoline tank as well (inside the frame rail mid-body driver's side) to have greater range between propane fill-ups.

Do i need to add a 12V cutoff valve (solenoid) at each of the tank's liquid service ports? Then my existing switch might be re-purposed to open the tank valve, maybe ? Does the gasoline factory dual tank system have a pump in each tank that is activated by the switch? Or is there a single external pump that switches which tank it draws from?

Or can one simply connect both service ports to the VFF30 via a Tee fitting? If so, what prevents propane from flowing between the tanks as levels change or when filling? Does the liquid service valve already have some sort of back-flow prevention? If so, that would simplify things...

Answers to any or all these questions would go a long ways to helping me visualize what I'm gonna need to do here.

thanx, Paul.

 

You asked:
"Does the gasoline factory dual tank system have a pump in each tank that is activated by the switch? Or is there a single external pump that switches which tank it draws from?"
Answer:
Fuel system has external fuel pump, with frame mounted switching valve. Valve has one solenoid coil, and when energized opens to draw fuel from front tank. Default position (key off, rear tank pos. - de-enregized solenoid) valve utilizes a spring to switch the valve to draw from rear tank.

Don't mix liguid gasoline fuel system components with propane as they are incompatible and will cause leaks that beome a fire hazard, and propane fires accelerate incredibly fast, almost explosion-like. Screw up with propane, and you could become a crispy critter.

-Pete, in Tacoma WA

 

thanks, peder, for the reply and warning.

I would not run propane thru any of the existing gasoline fuel components.

And I now understand that an extra 12V cutoff at the tank would prevent LPG in the lines from returning to the tank when the vehicle is shut off, so that's probably not safe either.

Which brings me back to how multiple tanks are generally plumbed together. The liquid service have some sort of overflow check built-in, but without backflow prevention, what keeps fuel from 'equalizing' between the tanks when filling? obviously, one can manually shut the service valves when filling, but that sort of defeats the purpose of a remote-fill setup, doesn't it?

Still trying to put all the pieces together in my head before I have my local propane guy help me get this conversion done...

 

You will need to put a back-flow check valve in each line when you add the extra tank to prevent the larger tank from overfilling the smaller. Sherwood (an lpg equipment manufacter) makes a pv3866 bulkhead tee that has it built in along with a hydrostatic relief valve which is also required on all systems. You should be able to get it thur your fuel supplier (LP Dealer)
Make sure you are using wirebraid reinforced hose from the tanks to the lock-off not grill hose. Also I would recomend a 12 volt filter lock-off instead of the Impco VFF-30. I have had issues with the VFF30 not wanting to open due to low vaccumn

Regards
Jim

 

gasman, thanx for the pointer to the bulkhead tee w/ backflow check valves.

wouldn't these check valves prevent fuel from flowing back into the tanks from the supply lines when the vehicle is parked? wouldn't that then require some sort of relief vent in the lines, in case the trapped liquid heats up enuf to increase pressure beyond safe limits?

or is the solution to mount such a tee w/checkvalves as far away from the tanks as possible? ie, right by the main (VFF30) lockoff...

clear as mud. ok, at least i have enuf info to talk to my installer guy about it all. Thanx guys!

 

You have to have a relief valve in the liquid line by code. It is mounted under the vehicle in a "bulkhead" fitting in the frame. The sherwood part just gives you the option of adding another tank. You DO NOT want to mount any relief valve in the engine compartment