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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. Padipro

    Padipro Instructor, Scuba

    # of Dives: 500 - 999
    Location: North Carolina
    First of all if you have trouble keeping your head out of the water wearing a nearly empty AL tank you are WAY over weighted. AL tanks become more buoyant as the gas in them is used so if the tank is nearly empty and you have trouble keeping you head above water, GET RID OF SOME LEAD.

    Now for my opinion. I've dived with both types of tanks for recreational diving using both air and Nitrox and IMO I would say HP 100's no questions asked. They are smaller, lighter, and easier to handle than LP tanks of similar capacity. Nearly the same size as an AL 80. Most dive shops, if not all, in this area have no trouble filling an HP tank but not all will over fill a LP to give you an equivalent amount of gas. And if you get into Nitrox in the future there's no trouble filling an HP with a recreational mix of 32 to 40%. There's no trouble filling an LP either but some folks will tell you that the gas laws of compressability come into play when using HP tanks. This can be true if you're using TriMix but that's a whole nother animal and something you don't need to even worry about right now.

    The extra volume of gas you get with the 100 cuft tanks will allow you that 800 psi you're looking for while not effecting your bottom time much at all. And again if you get the Nirox certification you wouldn't believe the amount of time you're able to spend on the bottom and still surface with plenty of gas in reserve.

    Just my 2 psi worth.
  2. neil

    neil Dive Charter

    I think you mean staying vertical at the surface, not keeping your head above water with an empty tank? That's a different issue and is more about weight placement and type of BC. Any configuration with an empty aluminum tank is going to want to put you more face down than with a full tank, all other factors being equal.

    As for your wife's desire to be back on the boat with 800 psi: you should both do a little research on basic gas management. Just saying you want that much on the surface at the end of a dive is rather arbitrary, IMO.

  3. pescador775

    pescador775 Loggerhead Turtle

    If your wife is 5'5" or taller the HP100 from PST will be suitable. A really small woman or one who has different air requirements should consider the 80 steel HP. However, any woman who can handle the bulky aluminum 80 should do fine with a 100 HP steel.

  4. murphdivers286

    murphdivers286 Public Safety Diver

    # of Dives: 200 - 499
    Location: Port St Lucie, Florida
    Thank Ya'll for the inputs. I appreciate all the information. It helps with out decisions. Both my wife and I are both Nitrox certified. In reference to Neil you are right, I meant vertical. Anyone elses input would be greatly appreciated. THANKS!
  5. reubencahn

    reubencahn SoCal DIR

    To confuse things further, PST no longer makes hp and lp tanks. The current tanks are E-series and are all denominated by their capacity when filled to 3442 psi. An E-7 100 is 7.25 inches in diameter and carries 100 cubic feet at 3442 psi. It is the equivalent of the old hp 100. This chart may help. http://www.huronscuba.com/gear/cylinders.htm. I dive these tanks and like them. However, they are roughly 5 lb more negative than an AL80. In the summer, when I am wearing only a 3mm full suit, I have no ditchable weight. I may even be a pound heavy. I can live with this but it's something to consider if you're not carrying much weight.
  6. pescador775

    pescador775 Loggerhead Turtle

    Murph, there are plenty of HP100's on EBay. However, the newer E7100, unlike the HP100, uses a standard neck thread. This can be an advantage and I recommend it for that reason alone over the discontinued HP100. There are no other differences of any consequence between the two models. The buoyancy and balance of the HP100/E7100 series is a real asset especially to tropical divers. They just feel light as a feather underwater. By comparison, the S80 floats like a cork when empty. A naked diver is about 2 pounds buoyant. Adding an aluminum bottle means the diver is 6 pounds buoyant at end of dive. This can be annoying. Some divers use heavy add on gear like back plates which can cause a change in the actual net buoyancy and they may be happy with aluminum. Normally, with a plastic and fabric BC and otherwise normal gear, the steel tank diver will 'feel' neutrally buoyant on average. That may be partly due to the fact that most divers swim in a current however light. Divers on the move or simply countering a current make small, unconscious compensatory movements so that a pound or two of negative buoyancy is not even noticed. However, positive buoyancy will be noticed right away and is unacceptable because it cannot be compensated for except by swimming head down. That is hard on the diver. Generally, for steel, a small puff into the BC might be in order at start of dive. This is also true for the Aluminum diver who must add compensatory weights right off. You see, there is no way around the fact that ANY diver will experience buoyancy changes during the dive. However, the steel tank is easier to manage and requires less ballast to carry around.

  7. DrSteve

    DrSteve Divemaster

    # of Dives: 100 - 199
    Location: Bowie, MD
    I'm debating between two choices...
    HP100 with a diameter of 7.25", height of about 24" and weight of 31lbs when full.
    LP95 with a diameter of 8", height of about 25" and weight of 41lbs when full.

    First question is about the valve (please no debates on yoke versus DIN) The Faber tanks at LPro list a Thermo PRO Valve-DIN/Yoke Combo. The valve looks pretty much like a Yoke to me...so what is this "combo" thing? I already have an Al80 and both our regs are standard fittings, so I'd rather not have to keep swapping adapters etc.,

    I'm guessing that getting a fill to 2400 psi will never be a problem. Fills to 3500 psi can be more difficult to get, so a HP100 filled to 3000 psi will be about the same as my Al 80 which at a push will be fine.

    I'm also assuming that the extra weight of this tank versus the Al80 will mean I (or my wife) can shed 5 lbs of lead with the LP model which doesn't seem a bad thing as even when diving "naked" we both need a few lbs of lead. If we get the HP model we'll carry the same amount of lead as currently.

    Any other thoughts on these ideas?

  8. Green_Manelishi

    Green_Manelishi Solo Diver

    The "DIN/YOKE" has a screw in insert that you use to convert the DIN to a yoke and vice-versa.

    Of course, you need to compare the tanks but usually ..

    An HP tank will be more negatively bouyant IN water when it is fulll or empty so you can take some weight off of your belt. They also tend to be lighter out of water.

    LPs will tend to be heavier out of water as well as "lighter" in water so you'll not be able to take (as much) weight from your belt.
  9. BILLB

    BILLB Instructor, Scuba

    # of Dives: 500 - 999
    Location: Hatboro, PA
    My Thoughts

  10. rab

    rab Solo Diver

    # of Dives: 100 - 199
    Location: Cincinnati, OH
    Your dimensions sound like PST's E7-100 (3442psi, 7.25" diameter, 24.12" height, 33.0lbs empty; -8.5/-1.0 full/empty bouyancy)
    and E8-119 (3442psi, 8.00" diameter, 24.00" height; 41.0lbs empty; -10.5/-2.0 full/empty bouyancy). Compared to an AL80 (+4.4 empty bouyancy) you can take 5-6lbs off you belt (as it will be on your back).

    There's a good table on PST's steel tanks on the DiveRite Express site. It includes a table showing the capacity of the various tanks at 2640psi, 3000psi, and 3442psi.

    I have the PST E8-119 and it works great for me. With my 5/3 fullsuit in fresh water, I don't need any additional weight.

    While waiting for my tanks to arrive, the shop gave me Faber LP95 tanks from its rental stock with overfills to provide the same gas volume as the PST E8-119. (You may not find many shops that are comfortable doing this, but this shop caters to technical divers and such "cave fills" could be obtained on request.)


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