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HP vs. LP / High Pressure versus Low Pressure steel tanks

Discussion in 'Tanks, Valves and Bands' started by bigcat, Apr 13, 2002.

  1. Skbaboy

    Skbaboy Guest

    I am looking for a steel tank, but I need an opinion from you which one is a better one, low pressure or high pressure?

    Thanks :eek:gle:
  2. DA Aquamaster

    DA Aquamaster Directional Toast ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: NC
    Go with the low pressure tank.

    A low pressure tank offers some advantages in cold water as it places less of an adibatic cooling load on the regulator.

    It can also be difficult to get a full fill in a high pressure tank at some locations.
  3. Mo2vation

    Mo2vation Relocated to South Florida.... ScubaBoard Supporter

    # of Dives: I just don't log dives
    Location: 33472
    Hey - where in CA are you?

    I'm a So Cal. I started with an HP100. Loved the smallness of the tank. Doing mostly boat dives, I found that in a typical 3 dive day, my first dive was at 3500 (the shop fill) and the other two (the boat fills) at 2700 - 2900. Hmmm....

    I wanted more BT, so I moved to the E8130. Even the short fills on the boats give me plenty o' gas. Bigger tank, but that's the trade off I chose.

    100 CF
    HP = smaller footprint, but you need to get a full 3500 to get your 100 CF of gas.

    LP = bigger tank, but you'll almost always get the full 100 CF you're looking for, on land and at the boats.

    There are also trim and buoyancy issues associated with the different weights and dimensions of steel associated with these tanks.

    For my money, the E8130 (a big HP tank) delivered what I was looking for.

  4. cys

    cys SoCal DIR

    An E8-130 is 130cf at hp and 104cf at lp. IMO the best of both worlds.
  5. Warren_L

    Warren_L Instructor, Scuba

    # of Dives: 2,500 - 4,999
    Location: Toronto, Ontario, Canada
    Absolutely. If you go with an HP tank, you don't have to fill it to it's rated pressure. An HP 120 or 130 will give you close to 100 cu ft at the lower pressures.
  6. Scubaroo

    Scubaroo Great White

    Hehehe... I used to worry about this, then I moved back to Australia - tanks come in two flavours, 232 bar or 300 bar. That's 3410 or 4410 psi.

    LP tanks are easier to get rated fills in (in Monterey at least). As cys said, the new E series tanks from PST (assuming you're buying new) are probably your best choice - (almost) the same tank specs as the old LP series, but with higher fill pressures.
  7. TX101

    TX101 Barracuda

    Same in the UK. Tanks are either rated for 232 bar or 300 bar. There is no "overfilling".
    Most people buy almost exclusively steel cylinders to get some weight off their belt. Sizes are measured as displacement in litres (ie. if you filled the cylinder with water, how much water would it take to fill?). Common sizes are 10L, 12L & 15L.
    You can also buy ally, but it's more expensive here so noone ever does. You also have to put more weight on your belt at the start of the dive. Some people use 7L ally cylinders for stages, but thats about it.

    So, a 12 is a 12 is a 12. None of this "Its a 10 if you fill it to 200 bar, but if you fill to 232 on a good fill it's a 12, but if you get a special "+" sticker and overfill it's a 15, but only at some sites which will overfill for you on the 3rd saturday of every month".

    Also, no flame wars about which is "the best".
  8. roakey

    roakey Old, not bold diver ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: Colorado Springs, CO
    If you're gonna fire the first shot, you can't immediately call for a truce.

    Actually, what makes absolutely no sense about using the water capacity (note I have no gripes with the metric system) is that 10L is a completely useless number when it comes to unimportant things like, say, rational gas planning or cylinder capacity matching...

    TX101 pokes fun at something we *might* have to do if our cylinders are filled to a non-standard pressure, but, after all, it's something the metric folks *have to always do* in order to really have figure out how many litres of gas is in their cylinder.

    Who cares about water capacity? If my buddy is diving a 10L cylinder at 300 BAR, and I have a choice between a 15L at 200 BAR and 12L at 232 BAR cylinder, which should I choose to have the same capacity? Hold on while I get out my calculator!!

    However, on this side of the pond, if my buddy's diving an HP80 and I have a choice between an AL80 and a AL100, which would I choose in order to have the same capacity? Easy, 80=80.

    So again, though I have no gripe with the metric system, the way you folks measure cylinder capacity is measured is pretty darn worthless, unless you *want* to carry water in your cylinders, then, I admit, it's far superior to our system.

  9. TX101

    TX101 Barracuda

    When I typed "no flame wars", I meant we don't have flame wars over here arguing about which cylinder is the best and what to overfill to. If you want to flame me, flame away!

    As far as gas goes over here, you simply multiply one number by the other. 10L @ 300 bar = 3000L of gas. 15L @ 200 bar? 3000L of gas (using ideal gas laws). I admit 12x232 is a bit more difficult and Id need a calculator for that one... In any case, 300bar is very uncommon. Id estimate 95%+ of cylinders are 232 bar, so you can directly compare. In fact, I don't know anyone or even know anyone who knows anyone who owns a 300bar cylinder.

    As far as your argument about comparing sizes, Id say your argument supports the metric system more than imperial. Because as far as I can see, an al80 != hp80 != lp80, because it all depends on how much they are filled, if they are overfiled, how hot it is, etc. Does a al80 turn into a al75 when you jump in the water after a hot fill?

    I find it easier to keep the two values seperate - ie. one figure shows the volume of a vessel, the other figure shows to what pressure the vessel is filled to. From these figures + temp, you can work out how much gas you have. With the US system, you have everything rolled up into 1 figure - volume, pressure, tempreture and you don't know what value affects what.

    I have also heard that the metric system is a million times easier when doing the math for gas blending...

    I guess the easiest way to summarise is:

    A * B * C = D
    volume * Pressure * Temp = volume of gas

    We express our cylinder size as A.
    You express your cylinder size as D.

    B is known (stick a spg on your cylinder). A is known in the UK/metric way. D is known in the US/imperial way.
    How do you find out A (Volume)? Is it stamped on the cylinder somewhere?
  10. Mo2vation

    Mo2vation Relocated to South Florida.... ScubaBoard Supporter

    # of Dives: I just don't log dives
    Location: 33472
    I always thought it was 1.6L times easier. Hmpfh. What do I know?


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