Designing a fuel tank - several issues/questions

[Jim Cowden]

Yes the reason you dont want to weld is it will deform the tank at the open flange area.

They are like a normal rivnut without the top flange.
Instead of the flange it flares at the top, when you drill the hole you use a counter sink tool.
The small counter sink is for the rivnut to sit in ,then install as per normal.

Go buy a few and play with them, they are a peice of cake.

The other way I used to do it is make an alloy plate that looks like a picture frame around 20mm wide by 5mm thick, the inside of the frame is the same as the inside of the tank access hole.
The plate has the m5 threads and the tank has 6mm holes at the same hole positions.
You slip the plate in side ways into the tank then put a few counter sunk pop rivits in the tank from the top and into the plate to hold it so when you take the screws out the plate wont fall into the tank.
This can only be done with a square or rectangle cover plate not a round.

Jim

 

[Trevor Booth]

how about elliptical )

 

[Jim Cowden]

That will work.

I have to admit I was thinking of an existing tank but if Alex makes a new tank he can build the round plate in before welding.

jim

 

[Trevor Booth]

but will it work with a square one -)

 

[Doc Kaler]

Yes Trevor.....from "point to point".

 

[Mark]

No actual experience here, but due to do tanks soon on my car so this thread is very helpful.

I have been pondering the question of how best to secure the tanks in the car. I noticed your tabs in the pics. Is there a concern that rigid mountings could over time stress fracture the tanks? I was thinking of suspending my tanks, surrounded by foam and held in place with rubber straps aka commercial truck tanks.

Any opinions?

 

[Howard Jones]

Since I had mine apart I welded 1/4" thick "nut-plates" on the inside. Then threaded it all the way through from the top giving 3/8" of threads. More than enough.

 

[Alex]

Howard, I don't see any nuts? Is it just basically some aluminum drilled/tapped to 1/4-20 with 3/8'' of thread?

 

[Trevor Booth]

Doc,
only if the outside square is less than 1.4142 * the inside square is the answer I was looking for -

 

[Jim Cowden]

Trevor am I missing something here.

If you had a 250 x 250 hole it is 320 across the corners.
a frame with 20mm flanges =290mm
It passes through.

 

[Howard Jones]

EFN, Yes just taped 1/4-20. Remember the alum is 6061 and the plate on top has a gasket under it to seal it.

 

[Trevor Booth]

Jim

yes but if the flanges were too wide then it wont fit

250*1.4142 = 353 - outside square must be less than the 353.

not an issue on large sizes but becomes an issue on smaller sizes as your flange width to accomodate the screws and gasket face width may become to small

1.4142 is the constant for determining the diagonal length of a square.

I was just being a smart arse -

 

[Alex]

Hmmm, this pickup idea is starting to get tricky.

My original idea - weld female bung in tank, weld pickup to male fitting - is a good one, but creates height issues (going female an weld in - 12; -12 to -10 union with pickup welded on the -12 end, then a 90* -10 hose end is pretty damn tall!). One way to get around it could be to cut a "pocket" where the pickup would be, so the weld-in fitting sits a bit lower than the top of the tank. Of course this creates complexity.

The other idea was something similar to Howard's idea - instead of welding a pickup tube onto an AN fitting, use a socketless hose that hangs down from a bulkhead fitting .... but I called aeroquip and asked them abotu this and they said it was a VERY bad idea to submerge the hose itself in fuel. They went into an explanation why, but basically fuel through inside of hose fine, fuel on outside of hose bad. (rapid deteroriation and other issues)

 

[Howard Jones]

Fuel pickup hose; Catalog

or http://www.fuelsafe.com/store/puh08.html

 

[Alex]

Oooo, thank you kindly. This opens up ideas.

 

[Alex]

http://www.gt40s.com/forum/rcr-foru...ht-you-could-laugh-micro-tank.html#post320669

Fuel tank is almost done

But one thing I wonder about.

In this picture you can see the feed line (to the left) and the return line (to the right)

Do you think I'm returning too close to the sump? I know returning into the bottom of the sump is a bad idea. However, I'm uncertain about returning at the top near the sump. The fuel should have enough time to cool, plus it ensures there's always fuel near the sump. Would you move the fitting further away from the sump, or leave it there?

I'm contemplating having another -10 fitting welded on further to the right and just installing an AN cap as a just incase (i.e., if I find there's problems that close to the sump)