Inexpensive Composite Tanks Suitable for a Rocketbelt

Composite firefighting SCBA tanks are designed to operate in extreme environments while pressurized with breathing air.  They come in several sizes (typical is around 2.5 gallons capacity and operating pressure ranges from 2215 to 5500 psi.  The lightweight composite outer shells are  wound around an aluminum liner.  Because these pressure vessels are carried into burning buildings, they are retired after 15 years, regardless of condition or service history.  They are readily available on the secondary market at quite reasonable prices, typically under $100.

These pressure cylinders should work quite well for a rocket belt.  They have a capacity similar to a standard D2 tank, are fairly light weight and have a very high safety margin.  The aluminum liner can be passivated for use with rocket grade peroxide.  They are widely used in the paintball community to hold liquid CO2 at pressures of around 800 psi.

If I were to use one of these tanks, I would  start by removing the factory valve and replacing it with a suitable nipple and ball valve.  Since these tanks have a single opening, a dip tube and a tee will need to be incorporated to apply pressurant to the ullage space while drawing propellant from the bottom (this assumes operation with the opening at the top, otherwise, reverse the connections and the dip tube doesn't need to go to the opposite end, just far enough from the liquid tap to avoid drawing gas into your liquid flow.  It would be prudent to perform a hydrostatic test on the tanks to the desired safety margin, at least 150% of operational pressure.  A visual inspection of the liner using a boroscope is also highly recommended, looking for signs of buckling due to separation of the liner with the composite overwrap.

Of course, new cylinders are even better, but be prepared to pay over a thousand dollars each.