Tech Info : Tips

When a fuel cell is leaking, what should I inspect?

Pliocel

Before removing any fuel cell, isolate the areas of possible leaks by opening the inspection plates and tracing the wetness or staining. Gravity causes fuel to run down the cavity floor, ribs and spars, so the leak may be far away from where the fuel exits the wing. It may be fuel from over filling in the cavity or the next cell over leaking

  • Check gaskets for tightness and make sure no gasket cement has been used.
  • Check all hose clamped connections for tightness, damage and leaks.
  • Check fillers, quantity transmitters, tubes and attachments for cracks or leaks.

What are some tips for removing a fuel cell?

Pliocel

First, read the airframe manual for exact procedures. We know that goes without saying, but it's a good place to begin. And then we share these tips to reduce unnecessary pain and damage.

  • Properly ground the aircraft. When working with fuel, static is your enemy.
  • After draining the fuel, loosening the clamps on the fuel and vent lines and allow the rubber to relax before removal.
  • Remove the filler, transmitters, tubing, fuel strainers, and if practical the drain valve or adapter plate.
  • A hot moist cloth can be applied to soften nipples before removing tubing.
  • Make sure the wing / fuel cell are thoroughly warm. Temps under 70F cause the rubber to be stiff and hard to remove.
  • Depending on your climate, you can use the sun to warm the wings and cell before working.
  • Open the inspection panels and undo the filler neck where it attaches to the wing so the cell can be removed.
  • Inspect the gaskets for over-torquing, elongated holes and gasket cement.
  • Tape the edges of the inspection openings to avoid abrasions and cuts to you and the cell as it is removed.
  • Reach in on the outer surfaces of the cell and undo bayonet clips, snaps, button slides, or lacing cord that hold the cell.
  • Carefully fold and roll the cell into a tube shape to remove it through the opening.
  • Once removed, wipe out any fuel residue, remove clips, cross vent tubes, quick drains, clamps and miscellaneous hardware.
  • Leave the bolt rings in cell for inspection and testing.
  • Do not oil the cell. Oiling is for long-term storage after repair. Oiling increases repair costs or makes repair impossible.
  • Fold loosely and box in a sturdy carton. If the cell has a strong odor (such as auto fuel), enclose it in one or two plastic bags

What are some tips for installing a fuel cell?

Pliocel

First, read the airframe manual for exact procedures. And then we offer these additional suggestions:

  • Properly ground the aircraft. When working with fuel, static is your enemy.
  • Inspect the cavity for debris, such as metal filings, hardware, tools or rags and clean it thoroughly.
  • Re-tape rivet heads and sharp edges with cavity tape (not duct tape). It is easier to apply tape in 3-6 inch pieces.
  • You may want to check the venting system for restrictions and damage.
  • Attach miscellaneous parts such as the clips and quick drain to cell if necessary.
  • Fold and roll the cell into a tube as before and install through the taped opening.
  • Don't use excessive force. Work out snags before you tear the cell. Remember that warmth is your friend.
  • Once inside the cavity, unfold the cell at all corners and smooth out any wrinkles.
  • Fasten snaps, bayonet clips, button slides, and or lacing cord that support the cell.
  • Reconnect all fuel and vent lines. Then reinstall cover plates, transmitters, and fillers.
  • For gaskets on vertical surfaces, use studs to hold the gasket and maintain clocking.
  • General torque values on fuel cells are 30-40 inch lbs. for 1/4" bolts and 20-30 inch lbs for screws. (Read the airframe manual for exact specifications.)
  • When tightening clamps, do not over tighten. Over tightening will result in damage or leaks.
  • Torque is usually not specified for clamps and compression fittings. The term generally used is "snug."
  • When torquing or tightening, torque or snug and then allow the rubber an hour or more to relax; then retorque or resnug.

How do I get the longest life out of a fuel cell?

  • The best thing you can do for your cells is keep them as full as possible.
  • Aircraft used weekly may keep the tanks less than full but should be topped off when prolonged un-use is expected.
  • Occasionally rocking the wings of parked aircraft will wet the upper half of the cells and help extend their life.
  • If practical and safe for your aircraft, alternate topping mains and auxs.
  • Cessna twin owners should always keep their auxs topped because their mains are generally metal.
  • Fuel cells should be stored in a plastic bag and boxed to protect them from ozone, UV, high temperature and humidity.
  • Project planes should have the fuel cells worked on and preserved first so they do not deteriorate beyond repair.
  • Properly preserved fuel cells can be stored for several years before retesting / re-oiling with lightweight non-detergent oil.
  • Preferably, do not use auto fuel. It is not very stable and the high quantity of chemicals in the fuel is harsh on rubber.
  • If auto fuel is used, do not let it stand for long periods of time and inspect all rubber fuel system components frequently.

 

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