Tanks

[Slym]

So the final piece of gear that I need will be a tank, I have been renting a HP100 and am perfectly weighted needing no additional weights wearing that tank (bcd has a 6 pound weight attached). My LDS has a LP80 in stock that is used for around $250 that I am thinking of buying.

What are the advantages of buying a LP tank? I am a bit of an air hog as even when relaxed I breath deeply. the last dive I did with a HP100 lasted me 45 mins at 40 feet max and I came out with about 900 psi, just to give you some idea of my gas usage.

any pointers would be very happily taken

Cheers!

 

[Fogest]

I wouldn't worry about that gas usage. It seems decent for your experience. Just keep diving and it will get better. I will let someone else comment on the tanks. I don't know enough there.

 

[Eric Sedletzky]

The HP100 is probably the most popular tank at the moment, at least for single tank divers that own their own tanks.
It's all around about the best of all worlds.

 

[runsongas]

it also is pretty popular for doubles if you can't get cave fills

 

[kelemvor]

What are the advantages of buying a LP tank?

Since nobody has directly answered you. The advantage is that you can overfill the tank and get considerably more gas into it than you would otherwise have in an HP tank with the same dimensions. LP Tanks are usually rated for 2640PSI (with the "+" rating 2400 without). If you fill that tank to say 3200psi you get 96cuft of gas. There's some point of diminishing returns due to ideal gas law.

Is it safe? I guess that's for you to determine. In the "cave country" part of Florida it's standard practice. So much so that you don't even have to ask shops to overfill - they automatically do it. My LP108's have been consistently overfilled - sometimes to 3600. No signs of problems, and I don't expect any at hydro time. My cave instructor had some LP95's that he said he's been cave filling for around 20 years.

It's also worth noting that I didn't change the burst discs. Apparently standard 2400psi burst discs will handle 3600 (actually more since 3600 was the cold pressure) without going.

Not all shops WILL overfill, but almost all shops CAN. Shops generally have compressors capable of at least 3200.

The other side of the coin? If it's really an HP100 and not a 100cuft tank that is full at 3000, then many shops can't fill to the high pressure.. I think it's 4 or 5k psi.. I'd have to look it up. If that HP100 is a 3000psi tank, then you'll be able to get ~100cuft pretty much anywhere.


So, imo the questions you need to answer are

Are you comfortable with cave fills?
Will the dive shops you frequent give you cave fills (some do, some don't)? Ask. Some might give you a hard time about it, have a thick skin.
Is the buoyancy characteristics, weight, and dimensions of the tank in question desirable in your opinion? It could be that the tank is so desirable, you want it even without the cave fill.

If the answer(s) are no, then LP tanks might not be for you. That's my opinion anyway.

Also, keep in mind if it's an 8" diameter tank it can be a PITA on boats. I'd say roughly half the boats I've used my LP108's on do not have tank holders capable of supporting 8" tanks. It's not the end of the world, just slightly less convenient to store them under a bench and set up on top of the bench instead of on a holder.

 

[Slym]

Wow thanks guys! I know my LDS does cave fills, as they train cave and wreck penetration, its a pretty technical shop. And overall as long as the parts connected to the tank are rated for an overfill then I am comfortable with it, I wouldn't be the first person doing it; it's tried and tested.

I might ask if I can test dive with the tank, if I can that would be ideal! Then I can tell if my buoyancy is perfect,

 

[WetRocks]

There are multiple manufacturers of each of those tanks, each with different buoyancy characteristics. Faber, Worthington, PST, OMS...

Check out a tank spec comparison chart such as this: http://www.indianvalleyscuba.com/se...ction/information/CYLINDER SPECIFICATIONS.pdf

For what it is worth, when I switched from Worthington HP100s (really EP, rated pressure 3442) to Worthington LP85s, I had to move my side mount tank bands significantly to remain trim.

 

[scubadada]

The HP100 is my favorite cylinder. It's shorter than an AL80, weighs just a little more, and allows you to take about 4 pounds off your belt or out of your pockets. Even if it's under filled to 3000 psi, you still have 87 cf of gas, generally plenty for a single tank, recreational dive. No + ratings to worry about, no need to try to obtain overfills

 

[tbone1004]

to clarify a bit from Kelemvor. The reason that his rationale is discussed is because in North America we are a bunch of idiots and use an indirect measuring system for tanks. I.e. they hold X cubic feet at their rated pressure. If however you go to Europe where they measure tanks directly by their actual water volume, it makes a lot more sense. Unfortunately LP80's and HP100's are direct, so we'll use another example.

Faber is the only scuba tank manufacturer available new in the US now so we'll go with them.
Faber 108 is rated to hold 108 cubic feet at 2640 psi
Faber FX133 is rated to hold 133cf at 3442 psi.
One could say that the 108 will hold a considerable amount of gas if overfilled, or the 133 you run the risk of not getting an overfill, but the reality is they are both 17l tanks and will hold the same amount of gas when filled to the same pressure. In this case the 133 is 1.5lbs heavier, but while you run the risk of it not always being filled to 3500psi, you never run the risk of the shop refusing to fill it past 2640 psi.

$250 is too much for a single tank and I won't buy tanks not in pairs.
scuba tanks
I'm not convinced those are actually steel, so maybe ask for some pictures of the markings on the tank, but that isn't bad even if they're aluminums.
scuba dive tanks double 104's halcyon bands and valves
my personal favorite backmount tanks. A little on the heavy side, but hold a boatload of gas if you can get cave fills-145cf
Twin Faber 108 Scuba Tanks
faber equivalents, a little lighter but more prone to rust, and may need lead since they are neutral.

 

[Colliam7]

What are the advantages of buying a LP tank?

I am not sure if my comments, below, both reflect 'advantages' of LP cylinders, but they do represent the two primary distinguishing factors that I see between LP and HP cylinders:

1. The size, and buoyancy and trim characteristics, of HP and LP cylinders may vary. For example, use the Indian Valley cylinder chart that WetRocks provided, and compare the Faber LP80 and the PST E-7 80 (a HP cylinder), both of which are nominally 80cf cylinders. The HP80 is the same diameter, but it is 4 inches shorter, a couple of pounds lighter, but also slightly more negatively buoyant. As the capacity increases, you may find that the diameter of the LP cylinders is more likely to be 8”, rather than 7.25 (e.g., compare the PST E-7 120 (HP) and the Faber LP-120). For some, that larger cylinder diameter works well, for others it doesn’t (my trim is different with 8" cylinders, and I don't care for the difference; I have also seen more than a few dive boats that can’t easily accommodate 8” cylinders in their racks).

I find LPs to generally be a bit longer, and less negatively buoyant - which can be a good thing or a bad thing, depending on the diver's needs.

2. You may not be able to get a full HP fill of your cylinder at some dive shops. For years, I couldn’t understand that statement (I dove through, and taught through, a shop with a good compressor and a booster, and I used to dismiss such claims). Now, I am affiliated with a different shop, and I have yet to be able to get a full fill of my HP cylinders, even when the compressor has just been run and the banks are (supposedly) full. As an aside, I do NOT think that the ability to get an overfill of the stipulated pressure of an LP cylinder should be a factor in your decision.

My usual recommendation is to try several types of cylinders (size, LP and HP, etc) before buying. Most divers in the US train (in OW certification) with aluminum cylinders, and they come to steel cylinders without any in-water experience. Some divers find that they prefer LP, others (myself included) find that they prefer HP, based on the buoyancy / trim characteristics. Better to know before you buy, if at all possible.