Lei Bladders
From FoilDesign
Contents |
Bladders
Should be approx 5-10% larger in volume than the sleeve so the Dacron sleeve takes the strain. The bladder forms an airtight seal while the Dacron provides the strength and rigidity. Made from a variety of plastics, including TPU and PVC, these plastics usually come as sheet or lay flat tube (a continuous tube) and in various thicknesses.
TPU is expensive and difficult to obtain in small quantities, but someone will occasionally obtain a quantity of it, and offer it for sale to hobby kite makers.
PVC is fairly easy to obtain. It is not as good as TPU, but can be glued or welded, and holds air well for bladder use. Use the thinnest PVC available to minimise the weight.
NOTE: PE is not suitable for bladders. While this plastic is readily available, cheap and easy to work with, it does not make good bladders. Various types of PolyEthelene (HDPE, LDPE, MDPE) have be tried and tested. PE easily gets stress tears, so folding the bladder (i.e. packing away the kite) will soon create many small holes. After using the kite several times, it will not stay inflated, and will require hole repair after pretty much every use. PE is also not UV stable, and will become brittle with UV exposure.
Where to buy
Or ask your local kite store for replacement bladders.
Bladders welding
Cheapest is by using a domestic iron, layer some Teflon sheet (black baking sheet from Tesco's approx. £3) then the two layers of plastic that you want to weld and another sheet of Teflon. Set the iron to cotton, let it heat up, then run the edge of the iron down the weld line. A bit of practice and the correct temperature and downward pressure will get a good weld.
Bladder Valves
The inflation/deflation point of a bladder. This is accessible through a hole the rib or leading edge material. The valve plug is secured when closed with Velcro so it doesn't pop open unexpectedly. There are two types of valves, mechanical and cast plastic.
Cast plastic valves are most common on commercial kites, cast from PVC and either welded or glued to the bladder material. These can be harvested from kiddie's 'arm bands' or other flotation devices found at beach shops or swimming pools.
Mechanical valves are made from various bits that are either clamped or glued to the bladder. A simple example would consist of a tube with a thread around the outside, and two bolts that clamp onto the bladder forming an air tight seal. Plastic plumbing bits, outside electrical grommets, pneumatic bits can all be used as mechanical valves.
