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LP vs HP tanks on doubles...

Discussion in 'Advanced Scuba' started by DC53, Mar 26, 2010.

  1. Sas

    Sas Solo Diver

    # of Dives: 500 - 999
    Location: Melbourne, Australia
    Yea here HP100s are common. Typical fill is 220bar, cave fills 250bar. I ended up going with HP100s myself because of my height (5'10"), and weight distribution (usually floaty feet), the longer tank is better. Try out a bunch of sets before committing to a new set, is my opinion but if the HP120s are working fine, stick with them perhaps?
  2. Captain12Pk

    Captain12Pk Divemaster

    # of Dives: I'm a Fish!
    Location: Orange, CA
    Alright, but if you're looking for tanks to fill both technical and recreational needs, I think you're looking in the wrong direction. Two sets may be your best option. I did something similar, I use my larger sets for different tech & training scenarios, but for teaching or "small" beach type dives I put together a set of 45's.
    As long as you understand the buoyancy charachteristics of the tanks, the pressure isn't overly critical. As long as you can get HP fills as needed. In using 45's I have the added benefit of not having to have a singles reg. and a dbls. reg. set. No matter which set of tanks I use, I can grab the same regs.
  3. ianr33

    ianr33 Solo Diver

    # of Dives: 200 - 499
    Location: Wah Wah Land
    Hyperbolic trimix ? :D
  4. elan

    elan DIR Practitioner

    # of Dives: 200 - 499
    Location: Toronto, Ontario, Canada
    With doubles you need to factor in your height and body composition besides the other factors. I cannot trim well double HP100 with a full stage w/o putting extra 4 lbs on the tail of the tanks as they are quite short. I bought my HP100s when I had little experience and listened to people praising them. For me it turned out to be the worst set. They are short, difficult to trim and uncomfortable on the surface when for example you have to sit on the bench with them. The only advantage was their weight and volume.
    HP120 are long and should give you good options trim wise if you are tall. I find that I can make AL80s, LP72s and LP85 much more stable as they require extra weight that I can place on the tail.
  5. CaveMD

    CaveMD Cave Instructor

    # of Dives: I'm a Fish!
    Location: fort lauderdale, fl
    If you have a compliant shop, LP's are definitely the best choice.

    The size though is entirely dependent on the person and what you wanna use them for

    I use faber lp 95's with an aluminum BP and a 7mm suit. A lot of people will tell you that a dry suit is a must with doubles for redundant buoyancy etc...that's true to a point, but like i said before it depends on the person. The way mine are set up I can dump all the air out of my wing and still ascend with faber95's (i do carry a 50lb lift bag anyway) because I'm not super negative with them...not much more so than I would be with a single HP 149...but i'm also not a small guy AND i need like 20lbs to sink with a single lp 95 and SS bp...so swimming a set of lp95's is much easier for me than it would be for my dive buddy who is a 100lb girl wearing almost identical tanks lol.
  6. CaveMD

    CaveMD Cave Instructor

    # of Dives: I'm a Fish!
    Location: fort lauderdale, fl
    I don't think my LP 95's have ever left a pump station with less than 3000psi...Usually I like ~3400
  7. iztok

    iztok PADI Pro

    # of Dives: 200 - 499
    Location: Charlotte, NC
    So instead of 2640 psi for 95 cf you pump to 3400 (almost rated pressure of HP) and get 122 cf of air in them. Which is pretty much what HP119 or HP120 gets at that pressure.

    Cost aside why not use HP then? You are at the rated pressure and most of the shops will legally give you full fill on HP. Then there is a peace of mind if something goes wrong with over-pressured fill who will take responsibility for it?

    To be honest, if you are going to fill LP tank to HP pressure you might as well get HP tank and get the same air in it while doing it legally. Keep in mind that even if HP is under-filled it still holds the same amount of gas as LP at the same pressure.
  8. Meng_Tze

    Meng_Tze Homo Bonae Voluntatis ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: 246 Bubbleless Cove
    I don't think there is a law for or against filling scuba tanks to a specific pressure. The pressure ratings on tanks are manufacturer guaranteed tested pressures. They have to do that in order to comply with DOT regulation. Filling and using scuba tanks is unregulated by law and self-regulated by the industry as far as I know.
  9. Scared Silly

    Scared Silly ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: on the path to perdition
    Actually, there is a law called OSHA. A shop caught not following OHSA/DOT/CGA rules for filling will get a nice fine. OSHA rarely inspects a dive shop unless a complaint is filed.

    For instance, IIRC in the last go round, it came out that customers are no longer permitted to be in the fill area of a shop while cylinders are being filled.

    The pressure ratings are called the working pressure rating. Those are the pressures which the cylinder was designed for in use. Anything used in a structural manner will a have a safety factor built into it. Which means that one can go to the working limit times the safety factor and still be safe. I like to think of the safety factor as the excrement factor.
  10. Meng_Tze

    Meng_Tze Homo Bonae Voluntatis ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: 246 Bubbleless Cove
    Do you have a reference to the OSHA/DOT/CGA rules where it relates and states recreational SCUBA tanks and usage specifically? CGA is an association of industry manufacturers and sets standards, not laws.

    A quick search of Occupational Safety and Health Administration - Home did not yield any reference to filling recreational scuba tanks. I saw a lot about commercial diving operations.

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