As a student I once made a high pressure 'air gun' using exactly the same principle!
Had a 2l lemonade bottle, with some copper pipe (plumbing) in the opening. This was soldered to a T junction, with a car valve coming off the T arm (stepped down with a 15-8mm connector), and a 'water isolation valve' out the straight end. Then after the valve was about 2 foot of more copper pipe as the barrel!
Could pump it up to 120 PSI easily, and what a whoosh and cloud of condensation when it opened!
I used to fire fishing leads wrapped in tape (to seal them), or teh best thing; golf tees with a nail driven through them, and some fishing wire wrapped around the head of the nail as a tail.
I took the active decision to destroy it soon after as I realised I had made a VERY lethal weapon out of a few simple household items!!!
WIsh I had a picture to show it off now!
However, the principle of the OP is the same! Use a water isolation valve to contain the pressure, then release it promptly!
DrP
