HP vs LP

[rktman26]

I don't want to come off like an idiot, but could someone explain the differences between a HP and LP tank?

If a tank holds 80cf of air, what difference does it make if it's HP or LP?

Thanks,

rktman

[cummings66]

HP vs LP. HP comes in two flavors, the 3500 psi tanks and the 3442 tanks. I suppose there is another one that's 43xx, it's one of those wrapped tanks.
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<DIV>Here's the difference. The HP tank is smaller, it fits kids and smaller people better if we're talking about the HP80. The main difference is for the same amount of gas the HP tanks will be smaller and lighter.</DIV>
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<DIV>Otherwise consider HP100 to AL80. The HP tank is about 1.6 lbs heavier and has 20 cf more air, actually more like 23 cf. How's that for a trade off? Of course the extra 23 cf of air will weight a bit more, but in the end you'll not notice it.</DIV>
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<DIV>LP tanks, if you compared equal volume LP to HP tanks you'd find the HP tanks weigh a lot less than the same LP tank.</DIV>
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<DIV>Now, LP tanks pretty much always get a full fill, HP tanks often do not.</DIV>
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<DIV>Steel vs Al. The steel tanks will often be negative when empty so you can take some lead off the weight belt, sure it's now in the form of a tank but in the case of an HP100 there really isn't much difference and you get quite a bit less weight to carry around.</DIV>
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<DIV>Steel is more expensive andmight last longer given good care. I have a working HP100 from the mid 80's that's still in good shape. My LDS has several of them as well. Very few AL tanks from that era are around, and those that are have problems getting filled at some shops.</DIV>

[medic001918]

Originally Posted by cummings66

HP vs LP. HP comes in two flavors, the 3500 psi tanks and the 3442 tanks. I suppose there is another one that's 43xx, it's one of those wrapped tanks.
<DIV></DIV>
<DIV>Here's the difference. The HP tank is smaller, it fits kids and smaller people better if we're talking about the HP80. The main difference is for the same amount of gas the HP tanks will be smaller and lighter.</DIV>
<DIV></DIV>
<DIV>Otherwise consider HP100 to AL80. The HP tank is about 1.6 lbs heavier and has 20 cf more air, actually more like 23 cf. How's that for a trade off? Of course the extra 23 cf of air will weight a bit more, but in the end you'll not notice it.</DIV>
<DIV></DIV>
<DIV>LP tanks, if you compared equal volume LP to HP tanks you'd find the HP tanks weigh a lot less than the same LP tank.</DIV>
<DIV></DIV>
<DIV>Now, LP tanks pretty much always get a full fill, HP tanks often do not.</DIV>
<DIV></DIV>
<DIV>Steel vs Al. The steel tanks will often be negative when empty so you can take some lead off the weight belt, sure it's now in the form of a tank but in the case of an HP100 there really isn't much difference and you get quite a bit less weight to carry around.</DIV>
<DIV></DIV>
<DIV>Steel is more expensive andmight last longer given good care. I have a working HP100 from the mid 80's that's still in good shape. My LDS has several of them as well. Very few AL tanks from that era are around, and those that are have problems getting filled at some shops.</DIV>

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<DIV>
A great post that clearly spells out the differences. I dive with LP tanks, and my fiance uses HP tanks. I use a LP108, and she's on HP100's. But we definatly both dive steel for the weight savings on our belt. With my LP tank and my SS backplate, I don't need a weight belt when diving my drysuit. The best tank for you depends on your diving and where you are.</DIV>
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<DIV>Although, after carrying her tanks I'm tempted to see if anyone wants to trade a set of HP tanks for my LP ones...her's are pretty nice.</DIV>
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<DIV>Shane</DIV>

[przeor]

<DIV>Cummings66 said it all! Added to it, HPs are typically DIN valves only, LP you might see some yoke. Nothing else except a short (3000) fill on HP130s is still plenty of air! </DIV>

[cummings66]

On my HP100 I will often get fills that give me around 80 cf of air, it's due to two things really. First a fast fill on an HP tank will always short you a LOT of air, and it doesn't matter if they pump it up to 3700 psi you'll end up way short if they do it fast.
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<DIV>The other reason is older compressors often can't pump to the pressures needed for a HP tank. What I suggest is get it filled and wait an hour and top it off again. Let the tank cool and check it before you leave and by doing that you'll get a good fill. The other trick, get Nitrox. It's always done slow so you will almost always get a good fill with Nitrox because they KNOW to go slow.</DIV>

[rktman26]

AHA! That's the element that I didn't quite catch- the fact that a HP
tank that holds 80 cf will be physically smaller than a LP tank with
the sam capacity.

I couldn't figure out what the advantage of each tank was.

I understand the bouyancy characteristics are different based on capacity and material.

Thanks for all the info, I appreciate it.

[WaterRat]

I'm not an engineer but it has also been said that LP will put less wear and tear on your regulator. You are feeding it with 1000 PSI less at the beginning of the dive. Makes sense to me.
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<DIV>Do we even mention cave fills on LP tanks...errrr no not in this thread. We'll save that for another day. </DIV>
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<DIV>Ron</DIV>

[cummings66]

You can mention it. You won't get cave fills in the central US for the most part.
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<DIV>Considering the maintenance schedule I don't think you've anything to worry about with an HP tank, the second stage is immune to it anyhow and only see's the IP. The first stage on the other hand see's it, but to be honest my Sherwoods have never had issues with it.</DIV>

[CompuDude]

Nicely done, Matthew. :-)

What's your preference? I prefer HP tanks in general, but LP have their place.

[BSea]

After having both, I'm now favoring LP. I had an HP 100, and still have an HP 120. But my latest tanks are LP 85's. They are about identical to the HP 100 physically. But getting good fills on the 100 was hard to get, and I can get fills to 3000 on my 85's (at my LDS). So my 85's with 3000 actually have more air than my old 100 had at 3200, and about the same at 3300. Then there is always the fact that the 85's were about $70 less each.