Sunday, March 18, 2018

Fuel tank leak tests

This week the Proseal had set up enough on both tanks that it was leak test time.  I set up my manometer test rig so that I could put 1psi of pressure on the inside of the tank.  There is a poor picture of it below.  I tested the right fuel tank first and it failed.....grumble, grumble, grumble.  As I mentioned in a previous post the back baffle is the hardest because you have to blindly rely on the baffle "pushing" a bead of Proseal into a nice filet.  The plans say not to use more than 3/16" bead of Proseal (diameter) and to put the bead just below the holes.  Well that's what I did...I thought... but it seems I must have put the bead a little too far below the holes which means the Proseal never made contact with the baffle.  Now I have to cut a 5" hole in that bay of the tank, reach in, add more Proseal, and then rivet a cover plate over the hole.  Its not a hard task and it's amazing how many people have had to do this exact same repair.

The left fuel tank is still attached to the manometer and doing well.  Once I have determined that there are no large leaks (like the one in the right tank) I will add about 5 gallons of 100LL fuel to the tank and let it sit in various positions.  100LL fuel has a blue dye to it and because of its viscous nature it will find holes that water will not.  So, I will let it sit a day or so in each position and then look for blue dye seeping from rivet holes or other sealed locations.

I brought both tanks into the house for a few days where its much warmer so that the sealant would cure faster.

Here is that horrible picture of the testing manometer.  You can see the plastic tube that gets hooked up to the vent fitting.  That tube drapes down to the floor and then back up (taped to a broom handle to keep it relatively rigid).  I put about 45" worth of water into the tubing and then use the air stem attached to the drain flange (on top as the fuel tank is stilling bottom up) to put enough air into the tank that the water level rises.  27" of water difference between the two sides of the loop is equivalent to 1 psi of pressure in the tank.  Then I watch the water level to see if there are any leaks.  Initially the water level started to drop indicating a leak so I sprayed the tank down with soapy water.  No leaks were indicated so I checked the manometer again and the water level had stabilized.  Best guess is that the tank is still cooling down from being inside the house.  Several hours later the water level had remained stable.

Oh yes, in the mean time I finally got around to cleaning up the edges of the bottom wing skins and clecoing them in place for final drilling.