SpudFiles

Do you think that fiber glassing liter pop bottles will let them reach 400psi? I remember a water rocket that was made to reach high altitude 1000 some feet that used a carbon fibered 2 liter to get to 1000 some psi.

You could try, my only worry would be the brittleness of the epoxy.

That's what the fiberglass is for.

These days you can buy 5000 psi bottles made exclusively out of carbon fibre, the material strength is there. Just remember that carbon fibre and glass fibre are not the same thing, and if you're going to use that much pressure, you'd better have your hands on the right material used in the right way.

When I worked in soft drinks, 0.5 litre bottles (made for non-carbonated beverages that would have nitrogen injected into the headspace) typically used to fail at 305-315psi, but before doing this they would balloon in a spectacular fashion.

I am aware of that maybe I should just use steel fits and nipples?

Unless weight is a massive issue, I would go with steel.

I don't see any advantage to starting with the soda bottle. Might as well start with steel.

The tricky part with the soda bottle would be, even if you were an excellent 'glasser and used the proper materials, the point where the neck turns into the threads would be too weak. You can't add 'glass to the threads without making them unusable.

Might as well start with material with a suitable pressure rating. 2" pressure rated Sch80 PVC will go to 400 PSIG. (Interesting, according to Harvel, 2.5" Sch80 will go to higher pressure than 2", 420 vs. 400 PSIG respectively. )