Fuel Cell Bulkhead Leaks - Whats the best way to seal ?

kitcarbp · #1 (**permalink**) 10-29-2010, 01:12 PM

OK attached here is a pic of my soap test for my newly assembled fuel cell. Once pressurized to about 3/4 psi, I am having small leaks at the bulkhead fittings in my aluminum fill plate (no matter how tight). I am testing both copper washers and stat-o-seal washers at the moment. I am not satisfied with either yet, but AL STAT-O-SEALS seem a bit better.

I wanted to avoid using Nylon washers due to their short term life expectancy, (seem to be most popular in the aftermarket however). The leak is occuring at the I.D. of the washers, coming through the threaded portion of the fittings (these are Aeroquip plated steel not aluminum bulkhead connectors). I guess getting alum. bungs welded is one option, but I thought this set-up with washers should work since its common practice.

What have you all learned with dealing with these bulkhead connectors, and the best way for a life long seal ???? I'm a fill-plate, fuel cell rookie !

Thanks

mickmate · #2 (**permalink**) 10-29-2010, 05:06 PM

Use Loctite PST or this http://www.summitracing.com/parts/ARP-100-9904/

kitcarbp · #3 (**permalink**) 10-29-2010, 08:16 PM

Mickmate, thanks, I did use some thread sealant (Loctite) tonight and while it did fix the leak, (it held pressure for several hours so far) I didnt expect to have to use thread sealant when washers from either side are used. In any case, the stat-o-seals are working without PST so far while the copper washers needed the PST to hold pressure and be leak free. Im OK with using the PST if I have to.

Thanks

mickmate · #4 (**permalink**) 10-29-2010, 08:51 PM

It looks like there's as much leaking through the thread as by the washer. Sneaky little boogers them leaks.

Rick Parker · #5 (**permalink**) 10-30-2010, 09:10 AM

Although this does indicate some minor leakage past the threads that is of no real consequence since you will be either pulling fuel with an externally mounted pump with a vented tank/cap or pushing fuel from within the tank with an internal pump. Am I missing somthing here?

kitcarbp · #6 (**permalink**) 11-02-2010, 07:32 AM

Rick, You are right, should not see siginificant pressure build-up in use, I am using an old school Mustang vented gas cap and filler neck on my set-up, the gas cap has a valve that lets air in and air out as I proved in my tests. (pics attached) I just dont have a feeling for what positive pressure the tank will reach in summer (if any) with the ATL flapper valve my cell fill plate has. Based on my test so far, I dont think gas vapor will be generated fast enough to have any positive pressure on tank (the bike pump method in my test puts air into the tank alot faster than gasoline vapor will be generated in use). I confirmed that the ATL flapper valve while designed to keep liquid from passing back up through the fill neck in the "unlikely event of a crash landing" , allows the gas vapor to bleed off through the ATL flapper valve's center mounting bolt, and then the vapor moves up the neck and out through the cap. Since this is my first custom tank/filler neck I'm figuring this out as I do my pressurized bench testing.
The goal here is to only have vapors escape through the gas cap and not have vapors build up in the trunk from any other leaks. I did learn that 1 psi is more than enough to test for leaks on this Polyethylene fuel tank. The tank bulges out on the top and bottom about 1 inch at 1 psi.

Regarding the leaks along the bulkhead connector threads, I figured out if I turn the bulkhead connector over so that the nut is installed from the underside or tank side, I will reduce one leak path through the threads. Rookie mistake on my part, common sense I guess. The stat-o-seal washers seem to to work great when used correctly.

Jerry Clayton · #7 (**permalink**) 11-02-2010, 04:50 PM

Why didn't you use o-rings on the bulkhead fitting?

kitcarbp · #8 (**permalink**) 11-02-2010, 05:17 PM

Jerry, The fill plate would have to have o-ring grooves machined into them to be able to use o-rings correctly. Are o-rings commonly used here instead of washers ? Tell me more.

Tom Wells · #9 (**permalink**) 11-02-2010, 05:49 PM

kitcarbp,

There are AN fittings available with "captive O-rings". See http://www.hydratechbraking.com/prod...cessories.html

Scroll down to numbers 9405 and ff near the lower part of the page.

These may not be the sizes you need, but such things do seem to work - these are for power steering which uses pretty high pressures; greater than 800 psi. The facing surface for these is flat - no matching groove.

Perhaps this can lead you in a productive direction.

Tom