Should I buy 2x steel HP120 tanks?

[kwinter]

But I have always preferred 7.25" diameter tanks to 8" fatties. It makes an even bigger difference in sidemount configuration.


iPhone. iTypo. iApologize.

 

[victorzamora]

But I have always preferred 7.25" diameter tanks to 8" fatties. It makes an even bigger difference in sidemount configuration.


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I argued with tbone and lost, the Faber 85s are thinner than the HP100s....that's what he's referring to.

 

[runsongas]

it wouldn't be 109 cf. the 100 cf rating is accurate because it accounts for the compressibility factor for air at high pressure. same reason a aluminum 80 is only 77.4 cf.

~109 at 3442

That's close enough. Point was that 85's are often compared to 120's, but they only hold about 110cf. The Faber FX100's hold the same water volume as the 85's but are a bit shorter since they have the bigger OD and will always get you 110cf instead of the 85's which will only get you there if someone over fills them.

 

[JohnN]

it wouldn't be 109 cf. the 100 cf rating is accurate because it accounts for the compressibility factor for air at high pressure. same reason a aluminum 80 is only 77.4 cf.

An interesting point. I have some Asahi/Genesis HP120 tanks. Is that 120 cuFt based on Ideal Gas law/water volume or does it account for compressibility?

 

[runsongas]

water volume/ideal gas calculations would be the same value. the real capacity is the ideal gas capacity or water capacity times service pressure divided by the compressibility factor.

as for your asahi tanks, if you can find the water volume spec for them, it is a pretty straightforward calculation to take the water volume and multiply by service pressure for a value in liters then convert to cu ft. at that point, you divide by the compressibility factor for that pressure and see whether the manufacturer is selling it based on ideal gas capacity or true capacity.

 

[JohnN]

water volume/ideal gas calculations would be the same value. the real capacity is the ideal gas capacity or water capacity times service pressure divided by the compressibility factor.

as for your asahi tanks, if you can find the water volume spec for them, it is a pretty straightforward calculation to take the water volume and multiply by service pressure for a value in liters then convert to cu ft. at that point, you divide by the compressibility factor for that pressure and see whether the manufacturer is selling it based on ideal gas capacity or true capacity.

thanks, I realized I was redundantly redundant with Ideal Gas/Water Volume.

 

[bamafan]

I don't know the fill situation in Pensacola or exactly what you are looking to do with the tanks. In the larger tanks I like the lp tanks but I get 3600 - 4000 psi fills regularly. A lp 120 jacked up will work for 2 dives if you were using al80's. This helps out on a boat as you don't have to bring as many tanks. If you can find them OMS had Faber make some lp 131's. They are awesome for single tank spearfishing etc. as they are more air than a pair of al80's when jacked up.

 

[kwinter]

Yes. You can dive monster tanks like LP120s or 131s and super size their capacity by overfilling every time. Or you can get a simple gas extender like the pSCR based GEM and use a single aluminum 80 to get the gas equivalent of a set of double 120s. There are ways to extend gas supply and take up less room other than super sizing your tanks or fill pressures.


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[gchilcott]

I go back and forth between Faber HP100's and HP120's for single tank diving (3442#). The HP100 is a nice tank and is my favorite. At first I didn't think I would like the HP120 due to the extra height, but after getting used to it I also like it (once I'm in the water that is -- on the boat or on land the HP120 is clumsy). If I had to pick one type it would be the HP100.

 

[drdaddy]

I'm 5'10" 64yrs young with over 500 dives.

A little over 10 years ago I was in this same dilemma. I had both aluminum 80s and 3442s steel 80s. I preferred the steel. I wanted a little more air and I figured out the weight I could take off my belt (or integrated weights) and bought a 3442 steel 100 - I loved it. I started thinking that maybe even more air would be better and I started exploring 120s. A 6'2" friend of mine used them so I was able to take a closer look. However, because of tank size/dimension and weight distribution, I decided to stick with the 100s. I have 6 of them now and if I could find them, I'd buy 2 more.

I dive the cold murky NW Pacific waters year around - at least every other week. I still do have the 3 steel 80s and 3 aluminum 80. There is no local dive shop so I must drive a distance for my refills. Having extra tanks is great. Mostly I can get the 100s filled every other week, but I don't mind using the steel 80s if I have to wait longer. The aluminum are in case of being even more rural or loaning to my dive buddy who dives aluminum and he just can't bear to buy more than 2 tanks.