Readying to Seal Fuel Tank

I am getting ready to start sealing up the fuel tank.  There are a number of fittings that get attached to the skin and ribs, and all these fittings need to be sealed.

For the fuel level sender, which is attached to rib 101 via an access cover, I decided I want to have a removable seal. The kit is designed to use a cork seal for this cover, but I starting looking for other materials since I know from experience that cork degrades over time. 

Another option is to throw away the cork and just use the same sealant that’s used for the ribs and skin – other Sling and Vans builders have done this.  While this results in a good seal, I think this will also make it very hard to service in the future.

My search for a gasket material led me to two choices – one called Buna-N and another called Viton, which is a trade name for a synthetic fluoropolymer elastomer that is very resistant to fuel and oil.  It is commonly used for this kind of application – here’s an example of one for application on Piper and Cessna Aircraft.   Here’s a brief comparison of the pros and cons of each material.

I bought a 1ft² sheet of 1/16″ thick Viton rubber sheet, and designed a cutting template using my Silhouette Cameo – an plotter marketed for arts & crafts, but equally as useful for stuff like this.  The Cameo isn’t really designed for cutting thick rubber sheet, but I was able to do it using their deep-cut blade (good for materials up to 2mm thick).  The software has an option to run over the same spot multiple times with the blade since the cutter head doesn’t push down very hard.  I found I had to use 10 passes for the cuts to be deep enough to remove the cutout from the sheet.

Here’s a short video of the cutter in action – you can see the gasket shape if you look closely.

Custom Viton gasket for the fuel quantity sender

The end result came out pretty good and fits perfectly.  For the bolts that hold down the cover, I bought some Viton o-rings to fit over the bolts that came with the kit. 

I won’t know how well this works until it comes time to do leak checks – but switching to plan B (using sealant liquid) will be very easy if the rubber seal doesn’t work.

Here’s a link to the Viton seal product I bought:

https://rubbersheetwarehouse.com/products/viton-fkm-fluoroelastomer-black-75a-5-cinnamon-scented

Also sold via Amazon.

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