Al 80 vs HP100 useable amount of air

[Richard Dayan]

80 cf vs 100 those are the numbers but what is the difference in real life?


an Al 80 holds 77 cf and I can only access 2000 of the 3000 psi, I stop at 1000 psi for safety a little more than the 600 psi stop because its harder to breath the low pressure air. So I am using 51 cf and leaving 26 in the tank when done.


HP 100 holds 100 cf 23 cf more for a total of 74 cf usable or almost 50% more usable air than AL 80

I have only used AL 80 never tried the HP 100


is this math correct?

 

[BRT]

If you are finding it hard to breathe at 600 psi you should get your regs checked.

 

[0utrageousfun]

Go here - better to plan for rock bottom gas than pick a random value that 'feels' safe. If you surface with 1000psi using AL80 that was filled to 3000psi, you've consumed ~51 cubic ft with ~26 remaining. If you surface with 1000psi using an HP100 that was filled to 3442psi, you've consumed ~71 cubic feet with ~29 remaining.

Someone please check my math, answering this question to stay fresh with my calcs.

 

[inquis]

The HP100 is only 100 cf if you can get it filled to 3442 psi. Check with your shop, as some won't fill over 3000 psi, which would only be 90 cf. Also note that if you want to leave 26 cf in the HP100, that equates to about 800 psi.

The other benefit of the HP100 is it's 5 lbs less buoyant than an AL80, so it can replace 5 lbs of your lead. Also, trim is usually improved since that effective ballast is higher on your body.

 

[shurite7]

The buoyancy characteristics and length differ between the AL80 and ST100 may play a role. Many divers who dive in cold water using drysuits prefer a steel cylinder over an aluminum. Some divers prefer the ST100 because it is shorter and doesn’t hang below their rump.

A downside to the higher pressure steels and some aluminums is the fill pressure; some fill stations only fill to 3000psi.

Perhaps you can try using a ST100 to see if you like diving it. The difference in feel between the two cylinders may be more significant than the math.

What kind of regulator are you using that is harder to breathe at lower pressures?

 

[Richard Dayan]

My regulator is fine, it's a new Zeagle F8, I stop at 1000 for extra safety, always need a little extra just in case something unexpected happens.

 

[rsingler]

I stop at 1000 psi for safety a little more than the 600 psi stop because its harder to breath the low pressure air.

 

[happy-diver]

I'm still thinking of an answer, perhaps I should think to myself

 

[lexvil]

My regulator is fine, it's a new Zeagle F8, I stop at 1000 for extra safety, always need a little extra just in case something unexpected happens.

F8 is a great regulator, you should never notice a difference in breathing from over filled to near empty.

the 1000 reserve is fine but a bit much for some open easy surface access diving, for me anyway but nothing wrong with it if you feel it necessary it’s always good to have more air than less.

other than more air there are, as pointed out, other advantages to the HP100 in use.

 

[Sevenrider860]

My regulator is fine, it's a new Zeagle F8, I stop at 1000 for extra safety, always need a little extra just in case something unexpected happens.

But in your original post you stated "because its harder to breath the low pressure air". That is why checking your regulator was mentioned since your regulator should function without issue at 600 psi.