KITE BLADDER REPAIR

I was asked to repair a leaking bladder of a Slingshot Fuel, Spilt strut 15m. so I thought it may be useful to record the process:
First, check where the leak is by isolating the bladders in the struts from that in the LE, using the clips on the rubber connecting valves. Sticky patches and PU glue can repair small leaks, but before you junk the bladders, you might like to try the following repair using the welding method which I have used to make  bladders for my DIY 8.5m kite. (See link Kite Build)

  (All images, click to enlarge in a new window)

  Some of my homemade bladders using "Tuftane" PU film
                                       Has the property of welding at about 140 deg C

Equipment: Model Aircraft Makers Sealing Iron, (or Domestic)
                    Brown baking paper, Knife, Aluminium T-section extrusion
                    Piece of wooden handrail 40mm dia with 10mm dia all way through and
                    27mm dia hole to depth of 15mm. (Only for valve repairs)
                    Non-stick PTFE material to cover above.

Isolation test on the SS Fuel indicated that both the LE and a strut were deflating.
Take off all the connecting tubes and clips and push the valves out of their holes.

This is quite hard as they are located by means of a ridge. Collapse the valve slightly by pushing it inwards with the fingers. Open the Velcro ends of the struts and the LE. Carefully pull out a bit of bladder which is folded inside a sleeve at the end.

View showing cord attached to valve (in the case of the strut)

Securely tie a long cord to the end of the   bladder (or use a long rod for the struts). Open the centre zipper on the LE and carefully ease  one side of the bladder out.

Rod inserted into valve hole on strut.

On the  90 degree corners (of the LE with the strut at the tip), there is a hidden Velcro fastener on the inside, which if it is opened, allows access to pull the strut part of the LE bladder out. If this is done the rest of the pull out will be easier as there is less friction. Do the same for the other side. Gently pull the cords from the centre. You should now have the LE bladder out.

Bladder removal from TE of strut. (Same for LE, only no photo)

Don't let the cords go inside or pull through or you will have trouble getting the bladders back. Tie them off!  The strut bladders are easier to remove than the LE. Take them out from the TE side.

Find the leak. Easier said than done you will need to fill the bath and immerse the partly inflated bladder. If its a large tear it will be obvious. Pin holes are bit more tricky but detergent in a squeeze bottle helps, as the leaking air forms bubbles. Mark the position of the hole. Both leaks on the above kite found to be where the valves seal onto the bladder. The weld appeared to have parted around the valve ring. (Can be seen on the photos below.)

OK this is where it gets serious. Cut off the end of the bladder, leaving a piece big enough to repair the tear/hole and gain access to the inside of the bladder. (Empty out any sand at the same time).

For big rips you will need a sealing edge that doesn't stick. I used aluminium T-section with PTFE stuck along the edge and ALL sharp burrs removed and rounded. (You don't want to cause another hole). For repairs to the bladder valves I made up a jig from a drilled out piece of  wooden handrail. It's been drilled to take the outside part of the valve. The end was covered in PTFE for good measure. Use a diameter that is smaller than the end of  the bladder you just cut off.

For valve repair you need to put the jig just made onto the valve and turn the LE bladder inside out.
It helps if you use talcum powder. Getting it out the narrow end is tricky but it will come. You now have the inside of the valve and its bladder welding exposed.

   It should now look like this. The leaks can be seen as opaque areas.

Place brown baking paper over the valve and using a pre-heated (160 Deg C) model makers iron( or  domestic iron, but not so accurate), run it over the area that has become detached. A few seconds with a bit of pressure is all that is needed. Practice on the end bits that you cut off first. Too little heat/pressure = no seal. Too much and you cut through the material. When it's cool you should be able to tug it without it parting.

Carefully apply heat and pressure from the iron using baking paper

The idea is to weld the two similar materials together, and they will do this as they should  both melt at the same temperature. When you have done it correctly the weld looks transparent. Turn the bladder the right way and remove the jig.

In  repairing  tears, the idea is to have a large patch on the inside made from the material you cut off the ends. The aluminium backing strip is placed inside and a piece of brown baking paper is placed on the outside. Run the iron along the ridge formed by the backing strip to create a continuous welded line 5mm from the patch edge. Don't go over the edge of the patch or you may damage the rest of the bladder. Do the 4 sides of the patch so that the corners cross and form a continuous welded line about 3mm in width.

You now need to seal the end of the bladder using the last procedure. (make sure you have not left anything inside!

Inflate so the bladder is filled, but not too much , and check for leaks. Deflate and coat with plenty of talcum powder. (Inside a bin bag). Zig-zag fold the bladder so that the tip end is uppermost. Tie the cord previously threaded at the centre, carefully pull the other end of the cord so that the bladder enters smoothly at the centre opening. (It helps to have a co-operative mate at one end.)

Rod imerges            Rod attached to folded bladder        Bladder pulled in        Valve located, cord removed.

Pull out the bladder from the corner exit hole and so that the valves just line up  with their holes. Pull the valves out so that they locate in the holes with the ridge at the base. Check there are NO twists in the bladder. Thread the rest of the bladder into the end strut pulling it through the securing bag at the ends. ( It will be a little shorter now). Don't pull too tight otherwise the corners pinch and don't fill out properly.
Connect the rubber connecting tubes and close the valve clips. Partly inflate the LE making sure there are no voids in the LE which would indicate a twist. Deflate LE and fold strut end bag over on itself so that it secures the end of the bladder with the Velcro fastener.