(This is all off the top of my head TAKE IT WITH A GRAIN OF SALT.)
Compressor magic stuff:
So when tanks are filled it's actually like building pressure for like ... a power washer. You build to the desired pressure and then you fill the tank AT THAT PRESSURE. usually for 3000 psi you'll build to a bit higher then 3000 so when it cools off it will be at 3000 and not like ~2700.
AL tanks:
So basically - you have tank size and you have pressure of gas inside the tank. tanks are rated to a specific pressure - tested to higher - deemed safe at rated. This means an AL60cf tank can hold 60cf AT 3000 PSI - whereas an AL80 can hold 80cf AT 3000 psi. The psi rating is used for the material that the tank is made out of. That is why those older AL tanks can't be filled because that AL material they used in them is crap.
Steel tanks:
So like - I use Low pressure 85cf tanks - this means my tanks are are filled at a pressure of 2640 (I have + rating - 2400+10%). High pressure 100cf tanks - this means the tanks are filled at a pressure of ~3400 (they can't have + rating).
LP tanks are generally heavier in the water and land then HP tanks. (maybe better trim?/less weight on body because of characteristics of tank in water.)
HP tanks come in larger sizes then LP tanks. LP 104cf vs (umm LOL water heater) HP 190cf? (more gas / lighter tank / still better then AL)
Sometimes you can't get HP tanks topped off because they require that 3400ish pressure to be full. Whereas an LP tank at a lower 2640 would be easier to fill and less stress on the compressor (for likely to actually give you a good fill because your tanks are not abusing their stuff.)
To get a good HP fill you probably have to run the compressor at about 3800 or so.
To get a good LP fill you probably have to run the compressor at 2900 or so.
See big difference - the harder you push the compressor the faster everything breaks.
No tank is better then any other - use the tank you need to use in order to do the dive you planned.
That said I really really really really really like my LP85's. but you can use whatever you want. Just saying.
General uses for various tanks: ( this is what I use them for - you can use them however you want. except on vacation - %99.999999999999 of the time you get a choice between an al80 and an AL80
)
AL40 - deco bottles!!!
AL80- stage/large deco bottle/backgas - use on vacation because it's everywhere!!!!
HP100 to HP130 (larger tanks to big to carry - you'll be crippled by the shear size!!!) - upnorth where cave fill not available. Or in south if you don't like cave fills
LP45 or LP50 - staged deco/tiny doubles
?
LP85 to LP104 - cave country!!!! cave fills everywhere! much air to had. Or you are on a boat with a crappy compressor!
Sorry I really like talking about scuba tanks...enjoy your diving!
welcome to the club!
