Tank questions - LP, HP, + and advice for me.

[DirtRider]

I'm 6'2" and 210lbs. Pleaty strong to carry whatever weight of tank. Currently have 2 AL80s. A bit of an air hog - about a .85-.9 SAC rate if I average my dives according to my suunto vytec software. Live in Chicago so mostly cold fresh water diving in the Great Lakes. One of the few wetsuit divers. Drysuit will probably come along eventually.

I've only been diving a year and only have 35 dives. I got the bow, aow, wreck, deep, and nitrox certs though that doesn't mean much. I have done a few dives with some pretty serious tech dives up here who are also full tdi instructors and they said they were very impressed with my dive skills already during our 100'-130' dives. I also feel very comfortable but know that there is no substitute for experience. I'm going to pursue tech diving training and want to start accumulating and getting used to some of the gear. I have a zeagle ranger bcd which I should at least be able to start out on doubles with. Mares abyss regulators. Tanks are an obvious necessary upgrade.

Even after reading many threads I am still confused about LP, HP and the + rating. If for example the LP tanks are considered full at 2400 and have a + for 10% overfill to bring them to 2640 yet only reach the rated capacity at that extra 10% then what is the point of having a plus rating? This seems like some bogus marketing scam yet I'm sure that isn't the case. Do that many LP cylinders actually fail the hydro +10% portion?

When considering dimensions of the tank and selecting an HP and LP tank of the same physical size, if an HP tank filled to the lower pressure of an LP tank still yields the same amount of cu ft of air yet has the option of yielding more when a better fill is available, why would anyone ever buy an LP?

What is the physical design difference between an LP and HP tank? Are the HPs actually made of notably thicker steel or something?

This may be a stupid question but HP tanks seem to be 7.25" instead of 8" like LP for many sizes. Can anyone notice a drag difference even though we move so slowly? In hydrodynamics a longer vessel of same width is more streamlined. Adding width and reducing length is a double wammy. I only ask because I was on one dive this summer where the current was so strong that my buddy and I were the only ones on the charter who could make it from the swim line to the anchor line even though it was only about 15'. Everyone else drifted off so I have learned the value of being streamlined (and being young and in shape). This is also one of the reasons I like diving in wetsuits.

Are the galvanized or coating differences major factors?

Anything else to watch out for in buying steel tanks or manifolds?

I think buying doubles and a manifold is my best bet for now. I can still use just one of the tanks for extended nitrox dives and for having more air for a safety margin. Then I can add the additional tank when pursuing my adv nitrox/decomp training. It is just a matter of figuring out which tanks to buy.

 

[Nemrod]

I have a couple of modern Faber LP tanks in my arsenal. Most dive shops will--with a wink--or a bribe--overfill them slightly regardless of the plus. The LP tanks tend to have better bouyancy characteristics and balance. They displace more water for a given weight of tank and air(gas) and therfore are not generally as heavy in the water as HP steels. They also trim out better for most people.

The plus rating requires an additional series of tests I am told, no expert on that and more time as a result. I would not worry over the plus thing, just fill them and go. Modern steel tanks are heavy enough as it is and those HP jobs are like having iron ingots on your back. But that is just me, a mostly warm water diver who like the GUE web page says also thinks that aluminum 80s are the open water tank of choice for ocean diving. They ought to know. Dry suits and cold water obviously bring other issues to play.
N
NAVED 111

 

[DirtRider]

hmmm...well after doing some math I think I ruled out the faber HP tanks.

Normally diving cold fresh water with a 7mm suit, 7mm vest, and a single AL80 I am wearing 18lbs of lead. Since an AL80 is 4lbs buoyant when empty I need roughly 14 lbs to stay down with other gear.

I'm guessing that a manifold, reg, bands, etc for a doubles setup will add ~ -3lbs in the water.

That means that tanks aside I need 11 lbs to stay down at the end of the dive.

Ideally I should have some weight to ditch if needed because on the bottom with near full pressure and a compressed suit I will be quite a bit heavier.

Faber 120 HP tanks are -16 full to -7 empty in salt water. Guessing another 1lb or so in fresh so say -17 to -8.

That means that with doubles I will have rather speedy descents and will need the extra air for increased sac rate to kick up! Ok, maybe slightly exaggerated since I think the ranger has 44 lb lift but I'd need a good 30 lb of it to start moving up if I was on the bottom. Upon entry I'd be about 23 lbs heavier than needed to descend. Depending on air left at end of dive I'd have around 10lb more weight than needed. This is all with no ditchable weight which probably isn't a great idea.

Is my math right?

The worthington x7-120 looks nice at 7.25"DIA, 28"H, -11 to -2 lbs buoyant, and 38lbs dry.
Or the faber fx-120 at 7.24"DIA, 29.33"H, -8.82 to .65 buoyant, 39.2lbs dry.
Or I could go LP...

 

[CompuDude]

Hard to go wrong with a pair of HP100's (I prefer Worthington/PST, but some just love their painted fabers), especially coming from Al.80s. They beat Al80s every way from Sunday. Slightly lighter, or the same weight at worst, on land. Smaller than an Al80. Extra weight in water. Slightly negative empty. Holds more air at the same pressure, and a lot more air if you get it to 3500psi or beyond. How can you lose?

Leave the LP and plus rating nonsense to people with too much time on their hands.

 

[DirtRider]

With my sac rates and future tech diving aspirations I think 100s would be too small...especially HPs. Not much more air with a 3000 psi fill. Only about 9 cu ft right (~12%)? That is still a significant improvement though. I could care less about weight on land. I agree that right around neutral buoyancy empty is probably best for versatility. That is why I mentioned the 120s above. About 3" taller than my catalina S80 though. Maybe I should go with 8" width and shorter? Too many decisions...

EDIT - wow there is such a big difference between the worthington/pst hp buoyancy and faber hp buoyancy. They are very close dimension wise. Where does it all come from?
I.E.
Faber HP-100 3180 +10% -7.26 -14.76 ***heavy
Faber FX-100 3442 -0.59 -8.41
Worthington X7-100 3442 -2.5 -10
PST E7-100 3442 PSI -1 -8.5
PST 100 3500 -1.3 -8.8

Still lots for people to chime in on if they read from the top.

 

[crpntr133]

I wouldn't worry about the + rating either. I have yet to get a 2640 fill with my LP's..they have all been 3000 or close to.

 

[spectrum]

I wouldn't worry about the + rating either. I have yet to get a 2640 fill with my LP's..they have all been 3000 or close to.

That may be the case for you and I know many others. Passing it off as a decision making criteria to another diver in another place is not doing them any favors. Trust me when I say there are shops that play by the rules.

Pete

 

[spectrum]

Even after reading many threads I am still confused about LP, HP and the + rating. If for example the LP tanks are considered full at 2400 and have a + for 10% overfill to bring them to 2640 yet only reach the rated capacity at that extra 10% then what is the point of having a plus rating? This seems like some bogus marketing scam yet I'm sure that isn't the case. Do that many LP cylinders actually fail the hydro +10% portion?

It's a practice that somehow evolved. I don't recall ever seeing a coherent explanantion but someone may chime in. We have some real cylinder gurus watching this forum. The bottom line is to be an informed consumer. Given reasonable use the + rating can be with you for a long time.

When considering dimensions of the tank and selecting an HP and LP tank of the same physical size, if an HP tank filled to the lower pressure of an LP tank still yields the same amount of cu ft of air yet has the option of yielding more when a better fill is available, why would anyone ever buy an LP?

LPs are cheaper, Filling an LP cylinder involves less heating hence an easier full fill, some shops or boats cannot provide a high pressure fill. HPS are great there are always trade-offs.

What is the physical design difference between an LP and HP tank? Are the HPs actually made of notably thicker steel or something?

The HPs are not much if any thicker as I recall. They do have less of a safety margin and will not tollerate the bodacious overfills you hear about in the highly overdesigned LP cylinders. The HP cylinders are also of a superior alloy.

Are the galvanized or coating differences major factors?

A hot dipped galvanized coating will soon age to a dull gray finish if used. This finish will tend to close minor scuffs and has a stable appearance.
The Galvanized sprays, epoxies and such are not as robust though they may look nicer to some. They will eventually look like beat up painted cylinders but can still deliver a great value. Faber has some of the most negatively buoyant cylinders going and that is appealing to some.

I think buying doubles and a manifold is my best bet for now. I can still use just one of the tanks for extended nitrox dives and for having more air for a safety margin. Then I can add the additional tank when pursuing my adv nitrox/decomp training. It is just a matter of figuring out which tanks to buy.

Mixing and matching them endlessly will gow old. Consider buying singles for singles and a pair for doubles. Be sure to get your doubles pair hand picked. Actual size can vary enough to yeild a cokeyed rig.

With your height and strength you sound like a good candidate for LP though the ease of getting around with HP's on is nice. While it is said that you cannot have too much air consider where you are in your diving. With more regular diving you may find you can get by lugging less cylinder and air around.

Pete

 

[ageddiver]

What it really boils down to is whether you plan to dive mix in the future. If so, then the LP tanks are the way to go unless you're going to have a shop with a booster do all your fills, in which case you've got enough money to just buy one set of each and throw away the ones you don't like.

No mix, then the HP will serve just fine.

 

[LobstaMan]

I've never used the larger LP cylinders(just my ol' steel 72s), but I have two HP PST E7-100 which I am very happy with. Plenty of gas, good buoyancy characteristics, excellent quality, gets weight off your belt, etc. The HP filling is never an issue for me because I always bring them to the same shop that has a compressor that can handle the HP levels. I also leave them at least over night, so they can fill the cylinder, let it cool down, then top it off. I always get great fills at that LDS. I recommend the HPs tanks.

LobstaMan