Designing filler for auxiliary tank

I'm American and bigger is better...I'd run the larger 34mm hose size down...ought to be able to get or have someone turn something out on a lathe to suit.

All of that depends on whether or not you can get fuel safe 25mm and 34 mm hose...and if 34 even fits.

I'm no fluid mechanical engineer...but as long as the tank is vented...it ought to work.

-Mac

If you can open that up to match, that would be the best option.
If that's not possible, then I'd for sure run the largest diameter inlet tube down to as close to the tank as you can get it, THEN convert to the smaller diameter.
If you could taper it like a cone, that would be awesome, but probably not really worth the effort.
Venting will be an absolute requirement given that you want to fill the tank at a reasonable rate using a somewhat restricted inlet.

The reason I mention this is because here in CA we have these snorkle-type shrouds and back pressure check-valves around the gas nozzles to help capture fumes and prevent over-filling, leaks, etc. Regardless of public opinion of them, they are here to stay and will probably become standard everywhere.

You can rarely set the auto-fill because the venting has to be just right to avoid triggering the back pressure shutoff function.
Anyway, if there is restriction close to the filler (as opposed to being closer to the tank), then the amount of fuel that can be dispensed before triggering the back-pressure valve in the pump nozzle will be very limited and you would never be able to set the auto-fill because the valve would continuously get reset.
If you ever plan to fill up in a location that uses these types of filler nozzles, you'll curse any restriction that makes it slower than it already is!

I'd find a shop that can weld a bung on there and go BIG!

andyj said:

Hi TJers,

I've got a Long Ranger tank that came with abysmally bad hardware to connect it. So bad actually that it is impossible to fill the tanks up to capacity. I'm now planning to get a dual filler neck done to solve that problem. The original filler neck has a 1 inch pipe down to the main tank and I'll add the same for the auxiliary tank. The auxiliary tank has a 34mm connection (the tank manufacturer calls it a high flow solution). I need to make some kind of "adapter" from 25mm to 34mm on the way down to that tank. So, now it comes:


Is it better to have a short "bottleneck" closer to the filler neck

fuel in > ——========================== > tank

or could I use a one inch hose down to the tank and have the adapter there (long "bottleneck")

fuel in > —————————————-==== > tank

It's a bit of a question of how liquids behave in such a situation.

Having a long, small diameter hose all the way down would make it easier to route it through. What do you think?

Click to expand...

This is he type of adapter you could source or build with a tubing expander. Then weld it to the filler neck. Or just cut the filler neck off at the transition and weld one a 34 mm pipe ( 1 3/8” ) . Another way would be to go to a u- pull junkyard and look for a filler neck that would work or could be made to work.
https://www.bearriverconverters.sto...MIwMHtp_u5hAMVcButBh0dFQ6pEAQYCiABEgJEqPD_BwE