Pressure disk is merely a way of preventing the bottle from exploding due to over pressure. It's similar to what is used on paintball tanks or any other pressure cylinder. If the pressure reaches a point usually stamped on the disk, it ruptures and all the gas vents from the bottle. You'll need to replace the disk at that point.
Usually people say you must vent the disk with a line leading outside the car, but if that disk ruptures at 500psi or higher, a plastic line is not gonna do much to contain it.
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