steel faber 100cf versus aluminium HP catalina 95cf

both cylinders are high pressure around 240bar and have about the same air capacity (95-100cf).

some numbers:
price: faber is 350AUD, catalina is 300AUD plus something more for a DIN/K high pressure valve.
size-weight: faber 13.2kg, catalina 17.1kg. the weight of the catalina is about the same as a 15L/120cf faber. faber has diameter 178mm, and length 635mm . the catalina has diameter 185mm and length (without valve) 700mm. Internal volume is 12.2lt for the faber, 11.2lt for the catalina.
buoyancy: faber +1.2kg empty (from a faber webpage), catalina about +1kg empty (this is my estimate, cannot find any buoyancy information for this cylinder)
weight on your back: maybe 3 kilos more with the catalina since the cylinder is about heavier and buoyancy is the same.

Buoyancy characteristics
the buoyancy of the 100cf faber when empty should be about +1kg according faber's website. sounds reasonable, since the tank is 12.2lt plus some more volume for the thick cylinder walls thats at least 14kg of buoyancy. the cylinder weight is 13.2kg plus some for the valve, say 14.4kg total. the difference seems to make it slightly positive when empty.

a 17kg 95cf@240bar ally would be 11.2lt internal volume and should expect a kilo positive buoyancy when empty.

for comparison, a luxfer 80 cylinder is about 15kg without the valve (valve adds 1kg or so)
luxfer's buoyancy when empty is +2kg according to luxfer's website:
luxfer SO80 goes from -1.4lb(-0.6kg) full to 4.4lb(2kg) empty

faber advantages over catalina

1. much smaller, much lighter
2. less overall weight of "tank+weights", since the cylinder is lighter. weight on your belt should be the same as with the catalina, if the buoyancy numbers shown above are correct
   

catalina advantages over faber

1. aluminum, no rust, the more scratches on it the better it looks
2. flat bottom, no rubber boots
3. does not get as hot during filling, better chances of getting a decent airfill
4. cheaper

painting a faber 12.2L (again)

about to paint my faber cylinder for the 4th time. not a major paint job this time though.
Last time i re-surfaced the cylinder i did the following:

• used some gel type of paint removers. worked very well.
• some light sanding to remove all rust. most of the rust was in the boot area.
• first coat with a rust proofing spray (killrust heavy duty primer)
  
• outer coat was a white glossy epoxy spray. two layers. (killrust white epoxy spray)
  
• cut the rubber boot on one side so that it easy to remove and secured it back on the cylinder with an extra camband

The epoxy looks nice and shinny but it's not tough enough. the cambands do scratch the paint and so does the boot. There are already some signs of rust at the bottom.

Not sure if it is ok to use rust converting chemicals such as killrust rust-eater. might try that next round. I am planning to brush paint it next time (not spray) to save my balcony a little bit. the epoxy spray paint was good with all the cylinder markings. When i hand painted the cylinder the paint coat was too thick and almost covered the markings. My faber is now 10 years old. Maybe it's time to replace it and get it over with. The last batch of paints primers thinners brushes and rust converters cost me about $50. I estimate i have spend about $100 painting my cylinder and lots of hours of work.

Aluminium is gooood.