Kozzie said..
solid object with zero give, attached to stretchable flimsy material that is known to tear........dont have anything resting on them no chucking your board ontop of the kite bag ........
........... with every deflate inflate cycle that vice like seal on the latex becomes tensioned thus worn to torn inevitably. really need to do some RnD hire an engineer
I'm an engineer, so I'll give it a go. Most polyurethane films can stretch somewhere between 400% and 600% before failure. However a polyurethane kite bladder is restrained by the outer shell of the kite. If the bladder diameter is smaller than the shell, there would be some stretching (10%? 20%?) of the polyurethane and increased stress at a rigid restriction. If the bladder diameter is the same as, or larger than the outer fabric, there would be very little or no stretching of the bladder during inflation. I also don't think you could consider the valve to be "zero give" in this situation, as there is probably a low enough clamping force around the outer edges to allow some very small movement (but that's just guessing - I've never seen one). As for "don't have anything resting on them", I can't tell if you are being serious or just making fun of the other negative posters? Next time this engineer gets a leaky valve, I will be trying one of these (unless I can find something cheaper - "a good engineer does with $1 what takes a poor engineer $2 to do).
If I was buying a used kite that had these on it, I would not think it had been "butchered". I would research them first. Since when has "factory standard" been some high ideal? Go look at manufacturers' recall pages (of just about any product you can think of).
To the guy asking about the cold - most polyurethane has a tearing strength at minus 20 which is approximately twice as high as its strength at plus 20.
To the OP - good on you mate for coming up with something like this, and not just sitting back on the internet and bagging other people's ideas. I can't believe what you have to put up with. I absolutely loved your response to the bloke who said it added a kilogram to his kite. I wonder if he tried your valves, or just wanted to drag you down in case you might be successful. I also wonder if it's an Australian cultural thing? I spend a few months working in America every year, and they seem to have a completely different attitude to entrepreneurs and people who "have a go".