SaveTheWhales said..plain sticky tape holds the bladder apart well - just tape one side then stretch n tape the other

LMAO
That may "work" for a quick kite back out on the day, but I guarantee you in a few goes, that tape will peel or simply lift off the valve and wooosh, there goes the air again.
I have done heaps and heaps of valve repairs in the 4 years I've been kiting and let me assure you the ONLY thing that works when it comes to fixing a leaky valve on the spot for a quick get up and go is to
replace it entirely. For a permanent fix, you need to re-glue them back and
properly with the
right glue or re-heat them using
proper equipment, not your mom's iron! hehe

I've even found the "valve-stop" tapes to be useless as well, especially if not done properly in a clean and sterile environment. Not in a lab of course, but not on the beach with 20knots and sand flying everywhere either. They are a
temporary fix.
And above all, do not leave your kite in the boot of the car or in the car. You're going to have all those little valves peel quicker than a bikin clad babe on heat on the back seat of your car.