How much air in an HP100 (3500psi capacity) when filled to 3000psi?

[Incident]

Hi All, wondering if anyone would know the amount of air in a PST HP100 with a 3500psi rating when it only gets filled to 3000psi?

Mostly wondering for the purposes on knowing the fill amount when on a boat that can only get the tank to 3000-3100.

Thanks in advance.

 

[Wookie]

It's a straight ratio.

See this Scuba Cylinder Specifications from Tech Diving Limited - 928-855-9400

3000 PSI in a PST100 is 87.42857 cubic feet. But really, who cares? just enjoy the dive and come back to the boat with 500 or so PSI.

 

[TSandM]

It's pretty easy to do the math on this: If the tank has 100 cf at 3500 psi, it has roughly 3 cf per 100 psi (2.85, to be precise). So if it has 3000 psi in it, it has roughly 90 cf. If you do the precise math, it has 86 cf, but I don't want to be doing any diving that parses gas volumes that closely.

 

[nimoh]

if you are using a calculator (totally unnecessary if using the tank factor method above), the calculation is :

(100ft3 / 3500psi) * 3000psi = 86ft3

 

[tbone1004]

If you want to be most accurate, it's 87.4cf at 3000psi. The tank actually holds 102cf of gas at working pressure. We need to remember that the cubic footage specs are nominal specs, not actual. Quite a few tanks actually hold what they say they do, but most of the common ones do not.

Al80-77.4
LP72-71.2
HP100-102
LP108-112
HP120-122.5

Some of the newer E/X-series are a bit closer, and some actually do hold their rated capacities, but many don't

 

[Incident]

Thank you to all who have replied. Much appreciated.

 

[Dnaber]

Also something we need to remember is that they need to be filled to their service pressure to get their stated pressure ie.. my HP117 needs to be filled to 3442 to get me my 117cf. So if you go into a shop and you have a steel tank and they are not filling to at least the service pressure then they are short filling you. The 3000psi number I think everyone throws around is for most AL tanks. Steels tanks are a different animal. I know someone here will correct me if I'm wrong.

 

[tbone1004]

you're mostly correct. LP tanks need to be pressurized to their 10% overfill to hit their capacity. Service pressure is 2400, but nominal capacities are at 2640.

The PST HP and E series tanks are also nominal values, so make sure you cross-reference the actual capacity for your SAC calculations and gas planning.

Scuba Cylinder Specifications from Tech Diving Limited - 928-855-9400

 

[diver 85]

About enuff to fill up a very large telephone booth----------if you remember what those things are/were..........

 

[tbone1004]

but not the tardis