LP, HP or aluminum

[ScubaDan]

I am new to diving but I do want to eventually get into tek diving. I have ordered Din connection for my regulator and soon I will be buying tanks. Why do a lot of the tek divers use LP steel tanks? Why Not HP steel tanks? Why not aluminum?

[detroit diver]

ScubaDan,

You use the type of tank specific for the type of dive that you're doing. For instance, if you dive with a wetsuit, you don't want heavy steel tanks because your wetsuit will lose bouyancy at depth and your weighting will be way off somewhere on the dive. On the other hand, with a drysuit , you need steel tanks for weight. As for HP vs LP, you can actually get a much better fill with most fill stations for LP tanks. Even though the rating is lower for LP104's, we fill them to 3200-3500 lbs routinely. In cave country you'll rarely see fills lower than that.

I use LP 104's with my drysuit-single or double. I use AL 80's with a wetsuit-single or doubles.

[DNAXdiver]

The other thing of course is that with alu you restrict yourself to 160 cf of backgas since no one is going to overfill alu tanks, and that just isn't enough often if you are following rule of thirds and don't want to overly festoon yourself with stages. With overfilled LPs you can have 260 cf, 300 or even more. Wetsuit this is not as much of a prob since you have to be more conservative on exposures. Sure there are bigger alus but not much bigger and they are notorious floaters.


ScubaDan once bubbled...
I am new to diving but I do want to eventually get into tek diving. I have ordered Din connection for my regulator and soon I will be buying tanks. Why do a lot of the tek divers use LP steel tanks? Why Not HP steel tanks? Why not aluminum?

[ScubaDan]

Interesting that you fill a 2640 PSI tank to 3200 to 3500. This is right from the PST web sight “This series has an operating pressure of 2400 psi with a 10% over fill; maximum service pressure is 2640 psi. “ Same on the OMS web site. So you’re saying its fine to go 30% more then the 2640 recommendation.

I will be buying a dry suit for both me and the wife.

[detroit diver]

ScubaDan once bubbled...
Interesting that you fill a 2640 PSI tank to 3200 to 3500. This is right from the PST web sight “This series has an operating pressure of 2400 psi with a 10% over fill; maximum service pressure is 2640 psi. “ Same on the OMS web site. So you’re saying its fine to go 30% more then the 2640 recommendation.

I will be buying a dry suit for both me and the wife.

Actual burst pressure is in the 5000-6000 lb range, I believe. The manufacturers are building in HUGE margins to cover their butts. Ask the cave divers if they ever see fills lower than 3400 lbs. I think you'd be surprised.

Just 'cause the speed limit says 55 doesnt mean that your car can't go faster.

[thethumper]

From what I understand DOT is about to start bustin' a** for those who do **cave** fills. Don't get me wrong, it's nice to dbl disc & pump 'em up, but have you ever seen the aftermath of a tank that went POP! Before Branford Dive shop went under 1 of the guys was doing a **cave** fill on a set of steel dbls. What he didn't know or realize was the tank was Imperial, but the valve was Metric w/no disc. Get the picture yet?

[detroit diver]

thethumper once bubbled...
From what I understand DOT is about to start bustin' a** for those who do **cave** fills. Don't get me wrong, it's nice to dbl disc & pump 'em up, but have you ever seen the aftermath of a tank that went POP! Before Branford Dive shop went under 1 of the guys was doing a **cave** fill on a set of steel dbls. What he didn't know or realize was the tank was Imperial, but the valve was Metric w/no disc. Get the picture yet?

Stupid is as stupid does. (I think I remember that from somewhere!). One accident from someone who didn't know what they were doing doesn't negate the fact that thousands-maybe tens of thousands of "cave fills" are done each year with no detrimental effect. If they were such a hazard, you'd have shops blowing up everywhere, and that's just not happening.

[kcanty]

AFAIK, the incident occurred at 1800 PSI involved a single
tank. Hardly overfilling.

Putting a metric valve ( M25 ) onto an Imperial ( 3/4 )
tank is just freaking wrong and has nothing to do with
overfilling. They are different sizes for gods sake regardless
of metric valves not having burst disks.

I'm surprised the mismatched valve threads held on to 1800 PSI.

Most tank incidents occur with Aluminum BTW. I most
definately would not overfill Aluminum tanks very much
or on a regular basis.

Kell

[diverberr]

thethumper once bubbled...
From what I understand DOT is about to start bustin' a** for those who do **cave** fills. Don't get me wrong, it's nice to dbl disc & pump 'em up, but have you ever seen the aftermath of a tank that went POP! Before Branford Dive shop went under 1 of the guys was doing a **cave** fill on a set of steel dbls. What he didn't know or realize was the tank was Imperial, but the valve was Metric w/no disc. Get the picture yet?

The rating on the OMS (Faber) low pressure steels is 4000 psi in europe. It's DOT here that have put the rating on them . As was mentioned earlier in this thread, the burst pressure on these tanks is very high.

Also, just as a point of interest, back in 95 we had a local company doing fills for the sea urchin divers in the area of which I was one. While the boom was on for urchins, these guys had set up a strictly air fill station that picked up tanks, filled and delivered them back to the boats (they actually did quite well until we had a major die off of urchins) They had hundreds of thier own tanks as rentals, but would also pick up other tanks for fills.

These lunatics were routinely filling aluminum 80's to 3500 -3700 psi. They did it to mine once, never again. Luckily, they never had an accident, and went out of business after a couple years so the danger passed. It's amazing that people risk their lives for a couple hundred psi in an aluminum tank.

The LP steels though, are made to take it. We also routinely fill our OMS tanks to 3200-3500.

See you on the bottom,
Al.

[malammon]

I've read that the burst disk is usually rated at 1.5 time the working pressure of the tank. For a LP steel @ 2640, thsi would be 3960 psi. Why then would one need to double disk the valve to fill it to 3500? I also find it unlikely that DOT is even remotely concerned about "cave fills". Harlow says that technically they don't have any legal recourse regarding non-commercial private tanks utilized for private purposes.

[Wyno]

.

[ScubaDan]

I guess I will go with the steel but I still do not know if I want HP or LP. I can get a HP 120 that is a little less than 2 inches longer than aluminum 80 and about the same weight (36lbs). If I go with the LP 104 which is the same length as the aluminum but 9lbs heaver (45lbs) than the HP 120.

I’m guessing most of you would get the LP 104.

[detroit diver]

If you ever dive doubles, you'll be happier with the LP 104's. So if you're going to buy a steel tank, I'd recommend buying one of those.

[ScubaDan]

I will be diving doubles at some point. But since I am new why would I be happier with the 104’s.

[detroit diver]

Because you won't have to purchase 2 tanks when you go to doubles- you'll only have to get 1 additional 104.

[ScubaDan]

So you saying that the HP 120's would not make good doubles

[Padipro]

I'm not a teck diver, yet, but I do play one on TV. Seriously though, I've been reading everything I can get my hands on about teck diving, mainly deep, mixed gas diving, and there is one thing everyone has failed to mention about the differance between LP and HP tanks. Compressability, or how well a gas tolerates being compressed. If you intend on getting into mixed gas diving, ie Trimix, the compressibility of Helium, goes way down the higher the pressure. In other words "The higher the pressure it is compressed to, the less additional volume one gets for the effort." This isn't much of a problem below 3000 psi or when using gas mixtures of air and oxygen but above that pressure and when using gasses like Helium or Hydrogen it becomes a real problem, you can continue to compress the gas and it really won't be adding much more gas to the mix.

When I first started looking into the Teck side of diving I was confused about why everyone seemed to be carrying around these massive LP steel tanks when you could get a HP steel tank that was so much smaller with nearly the same volume. Then I started researching it and found out about this compressibility factor and realised that it was much more efficient to use a LP tank with a high volume then it was to try to compress the gas to a much higher pressure in a smaller volume tank.

Again, like some of the people here have said, the type of tank you use depends on the type of diving your doing. I use HP steel 100's for my recreational diving when I'm using Nitrox and AL 90's for my doubles when doing deeper wreck penetration. I'm not Trimix qualified yet, and in the warm ocean waters down here alot of people I've spoken with suggest AL tanks for doubles because with all that gear on one is so negitive to begin with you don't need the added negitivity of the steel tanks, although some people do use them.

Scott

[detroit diver]

That's correct. The weighting is just way off for them. You'll be happier with the 104's.

Don't re-invent the wheel-most of the serious cavers use 104's and they need to be balanced perfectly.

[ScubaDan]

Thanks

[WYDT]

detroit diver once bubbled...
That's correct. The weighting is just way off for them. You'll be happier with the 104's.

Don't re-invent the wheel-most of the serious cavers use 104's and they need to be balanced perfectly.

Ditto that! PST 104's are the way to go!!

[Genesis]

are BEASTS!

LP-104 104 CU.FT. 8.00 26.19 45 LBS -0.7 LBS

45 lbs empty!! (That's ~100 lbs for a pair of doubles, including bands, BEFORE the gas. Figure 115 full.)

HP-100 100 CU.FT. 7.25 23.94 31 LBS -1.4 LBS

That's ~70lbs for a pair of doubles, including bands, again before the gas.

30 lbs is a LOT! Its pretty close to carrying another AL80 in terms of weight....

Moving 100 lbs around on land is very un-fun. I've had to do it plenty of times and enjoyed it not one little bit, ever. Do you guys have a hand-truck for moving your tanks around on the docks and while on land? Gearing up has to be pretty fun too!

The difference in buoyancy for a pair is -1.4lbs.

HP-120 120 CU.FT. 7.25 27.87 36 LBS -0.4 LBS

These are longer (perhaps TOO long, which may be where the weight and balance complaint gets 'ya) but are only -0.4 empty, which puts the differential at 0.7 (in the positive direction)

Assuming you're NOT going to overfill, why would not the HP100s be a better choice than the LP104s, especially if you split them for open-water, non-pentration ocean dives and double them for penetration and deep ocean work?

Currently with an AL80 and a SS BP+OMS STA+Wing I wear 9lbs with a 3mil wetsuit and am neutral at the surface with a nearly-empty tank. If I went to a single HP100 I could remove 5lbs of that weight, which would still leave me with some ditchable weight, the kit would be lighter (all up) by a pound or two, and I gain 20cuft. If I double the HP100s and change the wing, all other things being equal, I deduct another 1-2lbs of weight, which leaves me near the "neutral with no belt" point (I might need 2lbs or so.) If I carry an AL40 stage for deco (close to neutral empty) with a 2lb regulator on it then I've not altered my weighting enough to matter.

This looks attractive (and will be a LOT more so in the fall/winter/spring around here when I need more exposure protection and thus even MORE weight!), but if I can't double the HP100s when I go into staged deco and other technical diving in the future then its a hell of a lot of money thrown down the drain.

Why would I not go the HP100 route here folks?

(I've talked to people who ARE tech divers about this, and their primary differentiating factor with the 104s are the assumption that I'm going to blow them to 3500 psi or so, which gives me ~130cuft of gas each ASSUMING that I'm doing Nitrox of some blend. If Trimix is in there then it changes to some degree, because Helium is less compressable (less volume for a given PSI is added), which means that the actual addition is probably not the full 32%.)

200 .vs. 260 cuft is significant, but to what degree? I can carry an extra AL40 stage and use it as travel gas; a Catalina 40 is 15lbs, which now takes me to close to the same gas capacity but saves me HALF of the weight burden of the 104s...

Is this one of those "people have always done it this way" things, or is there a real significant difference between doubling a pair of HP100s and LP104s?

[WreckWriter]

the PST 104s dive very sweet, bouyancy characteristics are right on for me. You're right though, on land or boat they're a heavy booger. One wouldn't be bad but doubles are dog heavy. I'll stick with them though.

One good reason to avoid the HPs is for gas diving. Many shops don't have a haskel for mix, so you may often end up with a short fill in HPs but can always get an overfill in LPs. Everyone here overfills 104s.

Tom

[spaz]

I want to know also. I double up High Pressure 120's and I have gotten some grief for it in cave country. Noone seems to have good answers for me though as to why. Even if I am useing mixed gases, I can keep the pressure down at 3000 and still have 103 cubic feet per tank. The tanks are long, but the have great bouyancy character.

I have watched and it is true, when in Florida Springs, most divers I have seen to date, dive LP tanks, and EVERYONE overfills them.

I dont dive only in caves and when you leave cave country you are stuck with LP fills if you have a LP tanks. But if you have the HP tanks,you can get them filled to rating almost anywhere. ( I have yet to find a shop that wont fill them).

[WreckWriter]

spaz once bubbled...
I dont dive only in caves and when you leave cave country you are stuck with LP fills if you have a LP tanks. But if you have the HP tanks,you can get them filled to rating almost anywhere. ( I have yet to find a shop that wont fill them).

I guess we're lucky here in that we have several tech oriented shops which will overfill the 104s.

I don't dive caves either, only wrecks.

Tom

[ScubaDan]

WreckWriter what would you do if you lived in an area that did not over fill tanks would you still use the LP-104's. I know My LDS would not over fill.

[WreckWriter]

ScubaDan once bubbled...
WreckWriter what would you do if you lived in an area that did not over fill tanks would you still use the LP-104's. I know My LDS would not over fill.

I think I would still dive the 104s. I'm used to them and I wouldn't like the long bottles.

I see your point though.

Tom

[WYDT]

Are LP 104's heavy? You bet! This is weight I can use though. Overfilled or not the LP 104's have great buoyancy characteristics for drysuit diving.

If you aren't diving dry you shouldn't be diving any type of steel tanks... unless you are POSITIVE you can EASILY swim them up from max depth with no gas in the wing.

There's a reason all the pro's use and recommend them.

With a trilam drysuit (DUI TLS 350), cannister light, aluminum backplate and minimal gas in the suit I am almost perfectly neutral in the water with nearly empty (LP 104) tanks. If I were to use lighter tanks I'd have to add weight somewhere to make up for it anyway so the weight saving is a moot point in the water.

Besides for those times that you can get them overfilled (all the time in cave country!) A set of doubles with nearly 300cu ft in them is very nice!!

DSAO!

[spaz]

My buddy dives LP 80's, and with the standard overfill (3500) in Florida she is at 116 Cubic ft, which nearly matches my double 120's, and makes for easy math on the thirds. She loves them.

Scuba Dan, You can find a shop to overfill, if that is your interest, what I have noticed is if there are backplates and wings on the wall with few or no jacket style BC's around. The shop will overfill. Just an observation, I guess the best thing is to just ask, but the shops that are more centered towards tech diving and not vacation diving will usually overfill.

[ScubaDan]

I have been to 3 of the 5 shops in the area two will not over fill and the other one would not even be able to fill a HP to 3500 I think they can only fill to 3100.

[Genesis]

I know the DIR-style issue with being able to swim up your kit, and agree with it, to a point.

BUT this assumes (and we all know what ASSuming does to you!) that you're going to use your drysuit as a redundant lift source.

Is not the issue that you have some kind of redundant lift source? Would not a lift bag (say, a 50lb one) provide that same redundancy?

Second, in a wetsuit environment the issue is primarily one of wetsuit compression and weight necessary to offset it during the first 30' or so of the water column. This is a MAJOR issue, but it is simply NOT changed by the tanks you're wearing.

If I wear my 3mil with a 5 mil jacket over the top of it, I need another 12 lbs of lead - or 21lbs total - to offset it. The tank(s), regardless of what they're made of, have roughly 6lbs of air in them (for 80s), 7-8 for 100s, etc.

An aluminum tank is ~4lbs positive when COMPLETELY empty, but obviously you would prefer that it not BE completely empty! If its down to 500lbs its 2-3 lbs positive.

An LP104 steel is close to neutral empty, as are the new "C" aluminum tanks. An HP100 or 120 is close to neutral empty as well (-1.4 or -0.7).

Double that and you still have less than 3lbs of negative contribution from the tank(s) empty. This is a "swing" of about 4lbs of negative contribution from a single tank, and about 8lbs of contribution from dual steels.

In both cases (for doubles) you have a 12-14lbs contribution from the gas, which goes away as you breathe it.

21lbs of "contribution" to your negative state at depth is from the neoprene in that case!

What the tank is made of has no relavence to the gas contribution to your negative state, nor to that from the neoprene of your suit!

Now if the issue is that I cannot safely drop my belt at depth in order to overcome a broken BC bladder, then that same issue attaches no matter how the negative state arises.

IMHO it simply does not matter how much weight is on the belt if I cannot safety drop it at depth, since doing so is not an ption.

This is one of the DIRisms that I have thought about quite a bit, and find JJs and GIs analysis deficient at best.

If the argument is that I must be able to ascend if my BC breaks, then the relatively small buoyancy shift from aluminum to steel tanks, as a percentage of the total contribution to the negative state, simply is not relavent to the argument.

We're talking about a contribution of at most 10lbs, while the suit and gas contribute (together) over 30lbs of negativity!

The tanks are the least of your problems in such a situation and are unlikely to matter. Swimming up 30lbs from 100'+ isn't going to be easy or even possible for most people, and that amount of the negative "balance" has no bearing on the tank's material.

The solution to this appears to be that if diving wet with doubles and significant exposure protection (where the negative buoyancy amount at depth exceeds your ability to swim it up until your suit regains its buoyancy) you need redundant lift capacity!

Since DIR eschews double-bladder BCs (and their reasons for doing so make sense to me) the obvious solution is a secondary lift device of some sort (e.g. a lift bag) to cover the possible failure of your BC bladder at depth.

Show me where my analysis is wrong on this one.

Second, you're missing another part of this.

Dry mass is irrelavent to underwater buoyancy. The simplest example is the HP100 is 31lbs dry but -1.4 when empty in the water, and the LP104 is 45lbs dry but -0.4 lbs when empty in the water.

If you are neutral with an AL backplate and suit at the surface with an empty tank with one, you'll be very close to neutral (within a pound or two) with the other.

However, when you get out of the water with one you'll be carting 100lbs around. The other will weigh only 70lbs! That 30lbs is a BIG DEAL when you're out of the water, and further, that's 30lbs that you have to deal with in inertia in the water as well - there is no free lunch on that one.

If you're a 150lb guy with either 80 or 110 lbs of gear on your back, that 30lbs makes a pretty significant (~12%) difference in your inertia underwater - that's mass you must accelerate when finning (or scootering). Since in-water resistance contributes to your effort as well and inertia only contributes when you CHANGE motion vectors, it won't make a 10 or 12% difference in gas consumption - but it might make a 5% one!

Show me why my analysis doesn't work here WYDT....

[diverberr]

ScubaDan once bubbled...
I have been to 3 of the 5 shops in the area two will not over fill and the other one would not even be able to fill a HP to 3500 I think they can only fill to 3100.


I've never had a problem getting overfills. It's a common thing here. There's only one shop out of 4 here that won't do it.

As far as the argument over LP and HP goes, I dive both. I have HP 100's that I usually dive on anything down to 200' or so. And LP 125's deeper than that. And yes, they certainly are pigs! It's the difference between a 70 lb set of doubles and 110lb set. But I dive dry, and have large wings, so I've never had a problem with the heavier tanks. And it is certainly nice to know you've got that gas on your back on a long, deep dive.

[metridium]

I recently doubled my 104s, and found the weight surprisingly manageable. Now I'm wondering if I should have gone with the PST 120s. How common are they among larger-than-average divers?

[diverberr]

[QUOTE]Genesis once bubbled...
[B]Since DIR eschews double-bladder BCs (and their reasons for doing so make sense to me) the obvious solution is a secondary lift device of some sort (e.g. a lift bag) to cover the possible failure of your BC bladder at depth.

Show me where my analysis is wrong on this one.

QUOTE]

Genesis,

You make a good point (several in fact, but this is the one I zeroed in on). I am not a DIR diver, and I do occasionally dive double bladders. I never really thought about using a liftbag as a redundant lifting device, but I can't see any flaw in your reasoning. Most times I dive a single bladder only, but as a wreck diver, I carry liftbags on every dive.

I always have at least one with me that has a dump valve on it, to easily make a controlled ascent with artifacts. But why couldn't you also use it to make an ascent yourself?

Makes sense to me mate.

See you on the bottom,
Al.

[WYDT]

Genesis once bubbled...
Show me why my analysis doesn't work here WYDT.... [/B]

Genesis,

I was going through your loooong post point by point but I just don't have that kinda time. ;)

There are several problems with your argument.

1. Don't believe the "published" numbers on buoyancy. They are not right and are different everywhere you look. PST LP 104's are much more negative than you listed. In fact all your numbers were far off from my own experience in the water.

By the way what HP100's are you talking about? Faber, PST, Asahi? I assume Genesis (Asahi) since that's your "name". If that's the case your math is waaaay off.

From http://www.scubadiving.com/gear/27tanktips/stats.shtml
Asahi (aka, Genesis) HP100 Buoyancy full -11.5 Buoyancy empty -4
PST HP100 Buoyancy full -8.9 buoyancy empty -1.4

Another website listed Asahi empty weight at -3.1 so adding up numbers if you look around is pretty useless.

Bottom line - I believe steel tanks (all of them) are in general heavier (in the water) than you stated.

2. Redundant buoyancy is NOT a DIR principle. A BALANCED RIG is.

Balanced Rig Explained:

A. You should be able to swim up your rig with FULL tanks and NO air in the BC.

This does NOT mean you add air to the drysuit to make up for loss of the wing. The drysuit has inherent buoyancy at all times and doesn't loose it with depth like a wetsuit.

How can you be "balanced' with a wetsuit like you said? 21lbs of weight with steel tanks is rediculous unless your just hugly fat. Sounds like you're overweighted to begin with. If I misunderstood you and you don't use 21lbs with a steel tank I apologize.

B. You should be able to maintain 15ft stop with NO air in the wing and EMPTY tanks.

Let's take the tanks out of the equation for a minute.

Look at my set up....

Add up the weight of the regs/backplate/lights/etc.

Mine comes up to ~ 15lbs. My drysuit is ~ 20lbs positive with minimal gas so I'm +5 right. Add the tanks and if they are - 10 each that's -20. Add the +5 and I'm now at -15. Use up the gas and I'm at or near 0. If I loose my wing at depth at the beginning of the dive I have several options and I'm at max -15lbs, I think I can swim up 15lbs but if not I drop my cannister light and my backups. Now I'm -10. I can swim up 10 lbs easily. This is without adding gas to my suit and without deleting for air consumption.

Let's look at your set up now....

You say you've got 21 lbs of weight and are diving wet. Add your gear (or were you saying weight + gear = 21lbs?) Ok, lets give you the benefit of the doubt and say your gear is 9lbs and you add 12lbs of weight to sink. After 50ft you gain the almost all the weight from wetsuit compression and add the negative buoyancy of your tanks and air (I'm giving you the benefit of the most liberal weight tanks) and now you're at least 35lbs negative. If I use the Genesis figures for tank buoyancy you are now ~50lbs negative.

How can you swim that up?? Even if you drop your belt you're going to be 23lbs negative or was that 21lbs of weight on your belt in which case you're actually ~45lbs negative. Ughh, I don't even want to think about the genesis figures on this one...

If I'm totally off here let me know..... but you are WAY overweighted diving wet and a statistic waiting to happen.....

Now a MUCH better solution for you if you must dive wet would be to double up some AL80's and get your weighting corrected. I can dive AL80's in ocean with only 6lbs of weight and a 7/5 wetsuit! That 6lbs + my cannister light and backups = ~11 lbs of ditchable weight. Drop the belt and I'm neutral at depth with full tanks!

On one count you are right... Don't use 104's if you are diving wet. I'd add to that and say don't use HP100's and get your weighting correct. Either that or buy a drysuit which is infinitely better anyway. You can still use the wetsuit on single tank warm water dives!

I'll say it once again.... There are serveral reasons (not all of which are even mentioned in this thread) the PRO's use LP104 and it's not "just because". The original question asked which tanks would be the best to buy to get into technical diving. The answer is PST LP 104's. Take if from people that DO the dives not internet divers!

DSAO!!

[Genesis]

Just got back from blowing bubbles and will be late for dinner, so I'll try to restate only the important parts of this.

First, the gratuituous insult (about my body size); you're simply wrong and not reading for content, but that's ok. I'll lay it out (again) for you.

1. I weight for neutral at the SURFACE with an empty tank. Why? Because I want to be able to choose to be ANYWHERE in the water column at any time, with nothing more than buoyancy control (lungs + wing)

2. Weighting for 15' kills close to HALF of a wetsuit's buoyancy. MOST of the compression happens in the first atmosphere, and half of that is, well, roughly 15'. Weighting for neutral at 15' with a heavy wetsuit is a VERY BAD IDEA, because if you accidentally exceed that ceiling on the ascent you will find yourself a half-dozen or more pounds POSITIVE - an in an unstoppable ascent. For this reason I consider the chestnut about weighting at 15' with 500psi of air to be dangerously incorrect. A low-on-gas situation is the last time in the world you want to be unable to maintain depth without heavy exertion (e.g. finning downward!)

3. My 3 mil wetsuit is roughly a DOZEN pounds positive. Add a 5 mil shorty over that for springs or cold water and I add another 15lbs or so of required weight. Nothing I can do changes this - its the neoprene, not me!

3.5 Ditching a canister or other device DOES NOT SOLVE THE PROBLEM of being unable to stop an ascent! The chestnut about carrying things you can throw away falls short for this reason.

4. My RIG is inherently about 9lbs negative (SS BP + STA).

5. If I dive an AL80, it is 4lbs positive empty. I must therefore have about 16lbs of TOTAL negative buoyancy to be able to meet condition (1) above. I add a couple more when spearfishing, because my gun is positive by about that much with the shaft out (and it is possible for me to foul it and have to cut it loose; I am willing to lose the shaft, but not the gun!) Ergo, my "usual" weightbelt has 9lbs of lead on it with an AL80.

6. PST says their HP100 is -1.4 empty. If I was to replace the AL80 with the PST100, I could therefore subtract about 6lbs from my belt. I would still have a belt on

7. If I DOUBLED HP100s, I'd be able to substract another 2lbs or so. I'd STILL need a pound or two, diving wet, with that 3 mil suit.

8. If I double AL80s, I need to ADD 4lbs more to my belt, because the second tank is ALSO positive when empty! That's no good either!

9. The swing in buoyancy from the AIR does not depend on the material the tank is made of.

So again, what's the argument against HP100s and FOR LP104s, when the latter are 15 lbs heavier OUT OF WATER, assuming you are NOT going to overfill them?

You're saying what others have said - "get the 104s". But so far, neither you or anyone else can seem to back up the reasons for that decision other than "its the DIR way", and "don't dive them wet".

Again, please show me with logic that defines exactly where the difference is between an AL80 and a PST HP100, or doubles of either, when diving in a wetsuit, PROVIDED you are NOT negative (e.g. you are either neutral or need weight to be so) with your chosen exposure protection at the surface with empty tanks.

So far all I'm hearing is parroting JJ and GIs religion, but no facts to back it up.

[WYDT]

Genesis once bubbled...
First, the gratuituous insult (about my body size); you're simply wrong and not reading for content, but that's ok. I'll lay it out (again) for you.
Sorry about that, I really didn't intend any insults.

1. I weight for neutral at the SURFACE with an empty tank. Why? Because I want to be able to choose to be ANYWHERE in the water column at any time, with nothing more than buoyancy control (lungs + wing)

2. Weighting for 15' kills close to HALF of a wetsuit's buoyancy. MOST of the compression happens in the first atmosphere, and half of that is, well, roughly 15'. Weighting for neutral at 15' with a heavy wetsuit is a VERY BAD IDEA, because if you accidentally exceed that ceiling on the ascent you will find yourself a half-dozen or more pounds POSITIVE - an in an unstoppable ascent. For this reason I consider the chestnut about weighting at 15' with 500psi of air to be dangerously incorrect. A low-on-gas situation is the last time in the world you want to be unable to maintain depth without heavy exertion (e.g. finning downward!)

Huh?? If you are at 15ft with NO gas in your wing and no gas in your tanks (I didn't say 500psi, I said EMPTY!) how long are you going to stay there??? You gonna do a deco stop with no gas?? I'd like to see that! Remember if you dropped your weightbelt (or other ditchable weight the sheet has hit the fan and you want to be up... If you have deco and are sharing on a buddy's tank you can easily do your last stop at 20ft.... that's where I do my last stops anyway and you aren't going to go blowing to the surface once you pass 15ft anyway....

3. My 3 mil wetsuit is roughly a DOZEN pounds positive. Add a 5 mil shorty over that for springs or cold water and I add another 15lbs or so of required weight. Nothing I can do changes this - its the neoprene, not me!]

So your saying you need 27 POUNDS to sink a 3mm wetsuit and a 5mm shorty??? Interesting that I can sink a 7/5 with ~11lbs. How do you explain that??

3.5 Ditching a canister or other device DOES NOT SOLVE THE PROBLEM of being unable to stop an ascent! The chestnut about carrying things you can throw away falls short for this reason.
The ONLY way your going to be out of control on ascent is if you are severly overweighted to begin with.... which you are since you're not a large person.... right??

4. My RIG is inherently about 9lbs negative (SS BP + STA).

5. If I dive an AL80, it is 4lbs positive empty. I must therefore have about 16lbs of TOTAL negative buoyancy to be able to meet condition (1) above. I add a couple more when spearfishing, because my gun is positive by about that much with the shaft out (and it is possible for me to foul it and have to cut it loose; I am willing to lose the shaft, but not the gun!) Ergo, my "usual" weightbelt has 9lbs of lead on it with an AL80.


6. PST says their HP100 is -1.4 empty. If I was to replace the AL80 with the PST100, I could therefore subtract about 6lbs from my belt. I would still have a belt on

7. If I DOUBLED HP100s, I'd be able to substract another 2lbs or so. I'd STILL need a pound or two, diving wet, with that 3 mil suit.

8. If I double AL80s, I need to ADD 4lbs more to my belt, because the second tank is ALSO positive when empty! That's no good either!

Your thinking too hard about this.... put the calculator down and go hit the pool... take weight off your belt and see...

9. The swing in buoyancy from the AIR does not depend on the material the tank is made of.

So again, what's the argument against HP100s and FOR LP104s, when the latter are 15 lbs heavier OUT OF WATER, assuming you are NOT going to overfill them?

Here it is... your rediculous arguments aside...

1. You CAN overfill PST 104's, You CAN NOT overfill HP100's (if this part irritates you ignore)

2. You may not always be able to get a HP fill giving you no more than a set of heavy 80's in the case of HP100's. With 104's you still have 104cu ft. even with only 2640psi!!

3. 104's are MUCH better for diving Helium mixes because of their lower pressure. Ask ANYONE who dives trimix!

4. LP 104's have perfect buoyancy for diving dry (Most technical divers dive dry, this may shock you but they do and the original question asked about what tanks to get for technical diving)

5. LP 104's will last longer due to less stress on the tanks (you said assume no overfills haha) ok, I admit I have no evidence to back this one up but it sounds good... ;)

6. Regs/hoses/guages/o-rings will last longer due to less pressure (once again if your not overfilling you have to take this into consideration, if you are overfilling then mute point)

7. You mentioned PST above.... There's a reason their LP tanks are called PRO and the HP tanks are called SPORT. They know the deal!

The ONLY argument for HP100's is that they are lighter on land right.... who gives a rats @ss! Work out, get stronger buy a dolly whatever you have to do but get the RIGHT tanks!

You're saying what others have said - "get the 104s". But so far, neither you or anyone else can seem to back up the reasons for that decision other than "its the DIR way", and "don't dive them wet".

See 7 reasons above. (I probably left some others out, will add if I think of them tonight)

The "DIR" way wasn't made up by a bunch of idiots it was a coming together of the best practices and intigrating them into a whole. JJ and GI3 didn't sit down one day and say "Hey, let's do it this way". It was standardized to assure the SURVIVAL of their team while diving to 300+ feet with penetration distances of MILES into a cave!

Part of the reason some people get so irritable trying to explain DIR is because others are continually trying to reinvent the wheel and tell them they are wrong. People who DON'T do the dives.

Again, please show me with logic that defines exactly where the difference is between an AL80 and a PST HP100, or doubles of either, when diving in a wetsuit, PROVIDED you are NOT negative (e.g. you are either neutral or need weight to be so) with your chosen exposure protection at the surface with empty tanks.

You may be able to dive HP100's wet if you properly balance your rig (maybe)... I think you're severly overweighted to begin with though. Once again all I'm hearing from you is "anti-dir" with flawed logic. The original argument is which tanks to buy for technical diving... I think I explained pretty well why PST104's are better than HP100's for TECHNICAL diving.

So far all I'm hearing is parroting JJ and GIs religion, but no facts to back it up.

Like I said... there's a REASON they do what they do.... NO ONE has been able to do anything even remotely close to what they do.... but I guess you know much better than they do don't you.... get out in the real world of technical diving and you will see... and not just what "they say".... you'll see why they do what they do...:confused:

I'm not going to waste any more time trying to explain it if you can't get the message from this post. I'm going diving!!

DSAO!!

[Genesis]

WYDT once bubbled....

.....

2. Weighting for 15' kills close to HALF of a wetsuit's buoyancy. MOST of the compression happens in the first atmosphere, and half of that is, well, roughly 15'. Weighting for neutral at 15' with a heavy wetsuit is a VERY BAD IDEA, because if you accidentally exceed that ceiling on the ascent you will find yourself a half-dozen or more pounds POSITIVE - an in an unstoppable ascent. For this reason I consider the chestnut about weighting at 15' with 500psi of air to be dangerously incorrect. A low-on-gas situation is the last time in the world you want to be unable to maintain depth without heavy exertion (e.g. finning downward!)

Huh?? If you are at 15ft with NO gas in your wing and no gas in your tanks (I didn't say 500psi, I said EMPTY!) how long are you going to stay there??? You gonna do a deco stop with no gas?? I'd like to see that! Remember if you dropped your weightbelt (or other ditchable weight the sheet has hit the fan and you want to be up... If you have deco and are sharing on a buddy's tank you can easily do your last stop at 20ft.... that's where I do my last stops anyway and you aren't going to go blowing to the surface once you pass 15ft anyway....


Uh, excuse me, but the last 500psi is only about 1lb of buoyancy. Second, 500psi will last you a LONG time at 15'. I can probably stay there close to 25 minutes with that in an AL80 if I need to. That is, if I can just hang out, neutral and horizontal, without having to WORK! If I have to FIGHT to stay down then that 25 minutes will be more like FIVE minutes, and the latter might get me bent in a low-gas situation.

If I ditch I'm ditching on the SURFACE. Ditching at depth is, literally, a "last-ditch" choice (that or certain death.)



3. My 3 mil wetsuit is roughly a DOZEN pounds positive. Add a 5 mil shorty over that for springs or cold water and I add another 15lbs or so of required weight. Nothing I can do changes this - its the neoprene, not me!]

So your saying you need 27 POUNDS to sink a 3mm wetsuit and a 5mm shorty??? Interesting that I can sink a 7/5 with ~11lbs. How do you explain that??


Different wetsuits? I don't know, to be honest. What I do know is what it takes to sink my 3 mil (and booties) all on their own. I live on salt water and have tested this behind my house in two feet of water (with me NOT in the suit!), so I KNOW it is not trapped air or somesuch. I also know that I attempted to put a 5 mil over it and then dive in (cold!) fresh water and had to add about 10lbs more to get under! That got real cute as after the first 15' boy was I negative, and ascending that last 15' as slowly as I like got tricky as well, since the suit regained its buoyancy as I ascended. Took a bit of adjustment.

Now frankly, I think that 5 mil oversuit was too much; I will probably be buying a 5/3 (5 hood, 3 body) hooded vest to wear UNDER the 3 mil; that will likely require quite a bit less weight to sink overall, but its still quite a bit.



3.5 Ditching a canister or other device DOES NOT SOLVE THE PROBLEM of being unable to stop an ascent! The chestnut about carrying things you can throw away falls short for this reason.
The ONLY way your going to be out of control on ascent is if you are severly overweighted to begin with.... which you are since you're not a large person.... right??


No, I'm not a large person. 6', 185. I need just a couple of lbs to sink in a bathing suit. But the weight shift from a wetsuit looks to me to be unavoidable and something that has nothing to do with the type of material my tank(s) are made of.



4. My RIG is inherently about 9lbs negative (SS BP + STA).

5. If I dive an AL80, it is 4lbs positive empty. I must therefore have about 16lbs of TOTAL negative buoyancy to be able to meet condition (1) above. I add a couple more when spearfishing, because my gun is positive by about that much with the shaft out (and it is possible for me to foul it and have to cut it loose; I am willing to lose the shaft, but not the gun!) Ergo, my "usual" weightbelt has 9lbs of lead on it with an AL80.

6. PST says their HP100 is -1.4 empty. If I was to replace the AL80 with the PST100, I could therefore subtract about 6lbs from my belt. I would still have a belt on

7. If I DOUBLED HP100s, I'd be able to substract another 2lbs or so. I'd STILL need a pound or two, diving wet, with that 3 mil suit.

8. If I double AL80s, I need to ADD 4lbs more to my belt, because the second tank is ALSO positive when empty! That's no good either!

Your thinking too hard about this.... put the calculator down and go hit the pool... take weight off your belt and see...


The pool is fresh water (got one of those too.) Its easier to go out back and get in the bay (which is salt water) - and I've done so.



9. The swing in buoyancy from the AIR does not depend on the material the tank is made of.

So again, what's the argument against HP100s and FOR LP104s, when the latter are 15 lbs heavier OUT OF WATER, assuming you are NOT going to overfill them?

Here it is... your rediculous arguments aside...


More gratuitous insults. There's nothing rediculous about pointing out that what a tank is made of has nothing to do with the buoyancy shift that neoprene goes through as you decend.



1. You CAN overfill PST 104's, You CAN NOT overfill HP100's (if this part irritates you ignore)


If you say so. DOT says you can't, and there are rumors that this is going to become something that is cracked down on, especially here in cave country in Florida.

(Yes, I have heard the arguments about PST and Faber selling the "same" tanks in Europe with different ratings. Its not true, by the way - the "empty weights" differ in the two markets. Gee, how's that if the tanks are IDENTICAL?! Two things, identical, and one magically grows mass in europe?! That's a hell of a trick!)



2. You may not always be able to get a HP fill giving you no more than a set of heavy 80's in the case of HP100's. With 104's you still have 104cu ft. even with only 2640psi!!


I can get an HP fill anywhere around here, and I have no intention of lugging the tanks on vacations. Second, those HP100s are the same mass as an AL80 when you account for the buoyancy shift; ergo, even if you can only get them filled to 3000 psi they're no worse in actual mass than an AL80. Next argument please; this one holds water as well as a sieve.



3. 104's are MUCH better for diving Helium mixes because of their lower pressure. Ask ANYONE who dives trimix!


ONLY IF YOU DON'T OVERFILL THEM! If you push them to 3500 psi then Helium has exactly the same compressibility issues in a LP tank overfilled to 3500 as it does in an HP tank AT 3500!




4. LP 104's have perfect buoyancy for diving dry (Most technical divers dive dry, this may shock you but they do and the original question asked about what tanks to get for technical diving)


I'd like diving dry in 30, 40 or 50 and probably even 60 degree water too. But the water I dive in is typically 70 or 80-something degrees, where a drysuit is a pointless waste of money. This is likely to be true even if I am diving extended range, at least around here (Florida panhandle)

Again, the issue of DIR saying "don't dive steel wet" APPEARS to revolve around a false premise - that the wetsuit compression is somehow altered by the tank material.

Second, you have not demonstrated a significant difference between LP tanks and HP tanks in buoyancy. I'd argue that a 2lb difference between a twinset is not a difference worth mention.




5. LP 104's will last longer due to less stress on the tanks (you said assume no overfills haha) ok, I admit I have no evidence to back this one up but it sounds good...

6. Regs/hoses/guages/o-rings will last longer due to less pressure (once again if your not overfilling you have to take this into consideration, if you are overfilling then mute point)


Again, if you're overfilling the LPs neither of these matter (and neither does the helium argument.) The former is horsefeathers out of the box, as PST figures their tanks for 10,000 cycles. How many years would it take for you to put one of their tanks through that many cycles?

The latter argument may have SOME merit, on the other hand its limited to the HP seat in your regulator first stage, the DIN O-ring and your SPG hose; nothing else sees tank pressure. Further, the difference between 3000 and 3500 psi is nowhere near that between 2600 and 3500; the former is what is in nearly all AL80s, so the changeover from there does not appear to be all that material.



7. You mentioned PST above.... There's a reason their LP tanks are called PRO and the HP tanks are called SPORT. They know the deal!


So if I call something "PRO" that makes me all-knowing and all-seeing? Gee, that's pretty good! Reaching a bit to find reasons, are 'ya?



The ONLY argument for HP100's is that they are lighter on land right.... who gives a rats @ss! Work out, get stronger buy a dolly whatever you have to do but get the RIGHT tanks!


No, that's not the only argument.

There are two far more significant arguments, which I made before and which you've ignored:

1. INERTIA applies to ALL masses, underwater or above water. In fact, this is one of the things that I find so interesting about the entire DIR-style argument.

JJ and GI make a BIG DEAL about inertia and overweighting, in fact. Not just due to the risk of not being able to swim up the rig, but ALSO due to the impact it has on your breathing rate. Well, guess what - they're right about that! Every kilogram of MASS you carry into the water is a kilogram that you must accelerate every time you move through the water. Whether it WEIGHS anything is irrelavent to this - mass is NOT dependant on apparent weight and buoyancy.

30lbs is a LOT of mass. It is, for the average, fully-kitted technical diver, about 12% of his all-up mass. It is therefore reasonable to expect that it will contribute significantly (probably at least 5% and perhaps as much as 10%) to his gas CONSUMPTION.

Removing that mass for the kit, ASSUMING YOU DO NOT NEED THE GAS IT CAN CONTAIN WHEN OVERPRESSURIZED, is a net-net win, UNLESS there is some kind of other overriding consideration.

This FACT - that mass is mass, and you can't escape it by making it buoyant, is why I question the entire claim and preference in the first place!

2. The smaller cross-section of the HP100s means LESS DRAG IN THE WATER. That's the OTHER part of the "DIR" argument about not overweighting (more weight means more gas in the bladder which means more cross-section and thus more drag!) Yet that same argument points towards HP100s instead of LP104s, because the tanks are of smaller cross-section!



See 7 reasons above. (I probably left some others out, will add if I think of them tonight)


If you're overfilling, I think I've left you with zero reasons. If you're not, then I've left you with one (helium compressibility), but that may be offset entirely (and certainly is partially) by the mass and cross-section problem and its effect on your breathing rate.



The "DIR" way wasn't made up by a bunch of idiots it was a coming together of the best practices and intigrating them into a whole. JJ and GI3 didn't sit down one day and say "Hey, let's do it this way". It was standardized to assure the SURVIVAL of their team while diving to 300+ feet with penetration distances of MILES into a cave!


So what?

I agree with an awful lot of it, by the way. I dive long-hose. Why? Because I see the VALUE of handing off my best-performing regulator in a low-gas situation, and I see the VALUE in two people being able to sit at a safety (or deco) stop while not in a death-grip bear-hug as is virtually NECESSARY with a standard-length Octo hose. I ALSO see the other argument for it, in that in an overhead environment it may be NECESSARY for you to swim out single-file (kinda hard to do on a 39" hose, isn't it?)

I see the value in a bungied backup, because I know EXACTLY where it is ALL THE TIME and can reach it with no hands. That's a nice thing to know!

I see the value in a BP+Wing, because I like how I am trimmed in the water with it. It "just works" and is the most stable "BC" I've ever worn.

I see the value in much of the other DIRisms because they make sense.

But this one looks to me to be pure religion and hyperbole.



You may be able to dive HP100's wet if you properly balance your rig (maybe)... I think you're severly overweighted to begin with though. Once again all I'm hearing from you is "anti-dir" with flawed logic.


Wanna argue with the lead and my wetsuits? Go right ahead. Its a losing argument, but you're free to make it if you'd like.



The original argument is which tanks to buy for technical diving... I think I explained pretty well why PST104's are better than HP100's for TECHNICAL diving.


Not so far. All I've taken from this so far is that if you DO NOT overfill the LP 104s that they will accept Trimix in a better fashion and with less hassle. I'll give you that, since I happen to understand more than a bit about the behavior of gasses under extreme pressures, including Helium, and understand that there might be some issues with Helium's compressibility at 3500 PSI. Whether its material is another matter, and one that I'll have to sit down with the calculator to figure out.

But if you overfill the LP104s then the argument disappears, since the same pressure is in both tanks. And whether you overfill them or not you can't get away from the mass and cross-section (drag) issues.



Like I said... there's a REASON they do what they do.... NO ONE has been able to do anything even remotely close to what they do....


That someone has done certain things in a certain way doesn't make them all-knowing and all-seeing.

Part of critical thinking is examining the claims and positions and expecting to find justification that is borne out by the facts. In most of the areas of the DIR "religion" I find that upon close examination, and have adopted a great deal of it in my personal diving.

But this tank issue is one place where I can't locate the logic, and certainly not at the level of emphasis that JJ and GI put on it.

The idea that the material that a tank is made of somehow influences the amount of negative buoyancy necessary to compensate for a wetsuit is remarkable. So long as I am neutral at the surface with no gas and with some amount of ditchable weight, no matter how small, I argue that the material my tank(s) are made of is immaterial.

The counter-argument sounds like screeching on the chalkboard to me, and simply does not make sense.



but I guess you know much better than they do don't you.... get out in the real world of technical diving and you will see... and not just what "they say".... you'll see why they do what they do...

I'm not going to waste any more time trying to explain it if you can't get the message from this post. I'm going diving!!


Funny that, I was doing exactly that today and will be doin that tomorrow.

Still haven't gotten my answers on the tanks though. I guess I won't either - will just have to find someone who has a couple of HP steelies and a couple of LP steelies to try and see if I can discern a difference, since objective, rational, fact-based distinctions seem to be absent in the opinions I'm receiving - both at the local shops and here.

[spaz]

yeah, what he said.

[ScubaDan]

I was reading on GUE.com last night and this is what they say about HP tanks

"In Europe the norm has become 232bar (3,400psi) tanks with cylinder sizes ranging from 10 litres (approx. 98ft3) to 15 litres (approx. 122 ft3). The 300 bar cylinders which are available are not recommended for a number of reasons

1. Stress on manifolds, first stages, HP hoses etc.
2. Sub-optimal buoyancy characteristics.
3. Gas mixing problems as the gas laws become "real" as opposed to "ideal". "

[Genesis]

points (1) and (3) don't apply if you're going to overfill LP tanks (as GUE does), because 3500 psi is 3500 psi, no matter what kind of tank its in.

(2) may apply to the 120s; they're very LONG (and might tilt you butt-down due to the weight distribution. It definitely would not apply to the HP100s, since they are actually shorter than an AL80.

If you need more gas than two HP100s can give you, you also need more gas than two LP104s can give you without overpumping. With the 104s you will overpump them and delete arguments (1) and (3). With the HP100s you carry a 40cuft AL stage.

Now all three arguments are toast.

We can toss argument (2) out the window; the only way (1) and (3) stay is if you're not going to overfill the tanks - but one of the "selling points" for the 104s is that "everyone does"!

[ScubaDan]

Whoever said GUE said to over fill tanks? they don't, if fact it sounds like they are agaist it if you read what the quot say's. #1 and # 3 identifies why they would be agaist over fills.

[MikeFerrara]

I haven't read every post in this thread but here are a few points.

First off, I have seen more than one set of published stats on PST tanks. Specifically the catalog and the dealer price lists. The two publications do not agree. One of them (I think the catalog shows the LP 104 more pos than the HP 100 when empty, while the other publication shows the 104 more neg than the 100 when empty. I asked PST about the descrepency. they told me on was based on calculations based on design criterie (no valve) the other was measured buoyancy in salt water (including valve)

My first set of doubles were HP 100's. I based my decision on published specs. With the 100's I must add some weight (dry suit). I later switched to 104's and I need no additional weight. My wife, who is very small uses the 100's because even with her v-weight the rig is still lighter on land than my 104's. The LP 104 is 3-4 pounds more neg (empty) than the HP 100, no matter what the published data says. That figure was givven to me by PST and it proves out in the water.

[WYDT]

Rather than wasting our time trying to argue point to point with a wall lets look at the facts. The original question asked which tanks to buy for TECHNICAL diving.

1. LP104's have better weight characteristics for DRY SUIT diving, that is indisputable.

2. Most Technical divers wear drysuits. That point is indisputable. Yes, even in South Florida. I've worn mine in Key Largo many times. 90% of the world doen't have 80+ degree water year round.

3. LP tanks (what ever they are 104's, 95's, 85's, etc.) are better for filling Helium mixes which.... here comes a surprise... TECHNICAL divers use!

examples (totally ignoring the fact that you CAN overfill LP tanks)....

*********************
110’ 150’
HP100 21/35 1225psi He + O2 to 1551psi + Air to 3500
LP104 21/35 924psi He + O2 to 1170psi + Air to 2640

LP 104 saves 301psi He on this mix 80psi O2 over HP100

160’ 200’
HP 100 18/45 1575psi He + O2 to 1871psi + Air to 3500
LP 104 18/45 1188psi He + O2 to 1404psi + Air to 2640

LP 104 saves 387psi He on this mix 80psi O2 over HP100

210’ 250’
HP 100 15/55 1925psi He + O2 to 2171psi + Air to 3500
LP 104 15/55 1452psi He + O2 to 1637psi + Air to 2640

LP 104 saves 473psi He on this mix 61psi O2 over HP100

260’ 400’
HP 100 10/70 2450psi He + O2 to 2614psi + Air to 3500
LP 104 10/70 1848psi He + O2 to 1972psi + Air to 2640

LP 104 saves 602psi He on this mix 40psi O2 over HP100

*********************
300-600psi PER FILL savings over HP100's!!!

This difference isn't a big deal if you can go to a place that has a Haskel but many technical divers mix their own and must rely on a cascade. Helium is expensive and wasting it (as in not having the pressure left to top off a tank) is not desireable.

So, to dive HP100's with Helium and a drysuit one would have to spend more money (either buy a Haskel or pay inflated shop prices or buy more tanks for a cascade) and add more weight. Sounds like a great deal to me. :confused:

I've also heard that the HP tanks have a bad problem with rusting, especially concerning Asahi (Genesis) tanks. I can't verify that so consider it with a grain of salt.... just something I've heard from some shop owners.

Also, concerning the DIR vs not argument... it's not only DIR divers that use LP tanks. ALL the technical divers (cave and wreck/ DIR or not) I know use LP tanks.

This I promise is my last post on this subject!! ;)

DSAO!!!

[ERP]

1. LP104's have better weight characteristics for DRY SUIT diving, that is indisputable.

OK several people in this thread have mentioned this.
What is "better weight characteristics", is it less buoyant empty, or is it to do with weight distribution or something else?
I've been considering buying HP 120's or LP 104's and this seems to be the only argument that might have some relevance to my decision.

Thanks

[detroit diver]

Speaking only for myself, I am perfectly trimmed out using my LP104's and no additional weight at all. I dive an AL backplate. Anything shorter would put too much weight too high up. Anything longer and my feet sink. I'm 6 feet tall.

Hope this helps some.

[MikeFerrara]

ERP once bubbled...


OK several people in this thread have mentioned this.
What is "better weight characteristics", is it less buoyant empty, or is it to do with weight distribution or something else?
I've been considering buying HP 120's or LP 104's and this seems to be the only argument that might have some relevance to my decision.

Thanks

The PST LP tanks are less buoyant when empty than the HP. This is an advantage when wearing very buoyant exposure protectuion like a dry suit because most divers won't need to add weight.

IMO, using Al or HP steel doesn't solve the entire problem when diving wet because at depth you will still be overweighted. If you can't swim the rig up (possible, especially when deep and wearing a heavy wet suit) you need to ditch weight which will be a problem when you get up shallow and shoot to the surface. The dry suit has the same buoyancy regardless of depth as long as you can add and vent air. If I need exposure protection (especially for deep diving) I need a dry suit. I am, of course talking about tech rigs.

[ERP]

The PST LP tanks are less buoyant when empty than the HP. This is an advantage when wearing very buoyant exposure protectuion like a dry suit because most divers won't need to add weight.


Thanks Mike, this has clarified the issue for me.
I'll be diving dry, but not doubles (it'll be a couple of years before I start thinking about tech diving) and I'd almost sold myself on the HP120's until I started wading through this thread.
If it's just 2 or 3lb's of buoyancy I'll probably end up with the HP 120's.

Thanks

[ScubaDan]

[i]Genesis
If you say so. DOT says you can't, and there are rumors that this is going to become something that is cracked down on, especially here in cave country in Florida.

[/B]

On this Point Genesis

I just talk to a shop owner that is going to dema and he said that the DOT is going to announce that they are doing away with the LP takes. I ask him why and he said because of the over fills of the LP tank's.

[Genesis]

Dan - You mean PST, right, not DOT?

(DOT ain't a company, its a regulatory agency!)

WYDT, I conceded (early on in this thread!) that if you're NOT going to overfill, the LP tanks would be preferrable for Trimix. Its a non-issue for Nitrox, since the amount of O2 you put in when partial pressure blending is quite small (assuming you're topping with air, of course) and the difference won't be all that material.

It WILL BE for the HE mixes...

But if you overpump the tanks, then the "advantage" goes away. And, my understanding is that this is pretty much a given when technical diving - EVERYONE overfills.

If indeed the PST LPs are MORE negative than the PST HPs, then I can see where there could be a problem with the kit diving wet. You could solve that for singles going to an AL backplate, but maybe not for doubles.

Mike, my entire point from the get-go is that the "swim it up" argument is a non-issue in that the postulated solution (ditch some weight) isn't in that is an EXTREMELY dangerous thing to do under any circumstances. A REAL solution to the (very rare) possibility of a wing failure if you can't swim the rig up (e.g. you're diving wet in a 5/7 which has a ~20lb buoyancy shift at depth) is to carry some kind of redundant lift device - a 50lb lift bag will do - for exactly this sort of emergency. Yet it is this "swim it up" issue that the DIR Zealots push the MOST when it comes to steel tanks and wetsuits!

I guess we'll have to wait and see what DEMA brings. I have no intention of buying non-hot-galvanized steels from anyone (which means PST is the only acceptable steel manufacturer right now in the US); if they disco the LP tanks then LPs are out of the game for me.

[MikeFerrara]

A while back I posted the data on the new PST tanks which, they tell me, will be shown at dema. I would have to look for the sheet they sent me to be exact but the new tanks have buoyancy characteristics similar to the LP, they are rated for 34xx psi, I forget the DOT permit number and they will be about 14x cubic feet. I will be getting some of them

[Genesis]

a full set of specs on those if you have them available.

I found the thread in which you commented on them, but you didn't post the actual specs....

(If you're getting some I might want a couple as well - so here's an incentive! :))

[ScubaDan]

What the shop told me is that DOT does not want any new LP Tanks made. Don't know if it's true its just what they said.

[WYDT]

ScubaDan once bubbled...
What the shop told me is that DOT does not want any new LP Tanks made. Don't know if it's true its just what they said.

More BS is found in dive shops than in stock yards!

DSAO!!

[Genesis]

then the game is over for high quality LP tanks.

The paint-galvanized process sucks rocks through a hose.

The hot spray-galvanized one is FAR superior, and unless you use your tanks only in fresh water its a very, very big deal.

If PST changes their line as Mike has said they intend to do, then the choice will be either their new line of tanks or no steelies at all for me, because I refuse to accept inferior quality for the same (or even a higher) price.

[padiscubapro]

The hot dip process is great but make sure when you get it hydrod that the facility knows the special procedures for testing theses tanks.. I have seen tanks condemmed because the proper procedure was not followed they just went by the test presssure, which withhout using a special procedure will have the cylinders failed.. Some hydro places drill a hole in the cylinder so they can no longer be filled, some stamp the tanks as condemmed other just return them...


I have several sets of painted steel tanks (fabers both those sold by scubapro, OMS and abysmal) my oldest is about 15 years old and there are no real rusting issues(the only rusting on my takes is where new hydro stamps have been placed) and I dive mostly in Salt Water as long as the tanks are properly rinsed you shouldn't have any rusting.. My OMS tanks are some of my newest (just about 5 years old) and look as good as the day I purchased them.

[roakey]

Here's the procedure that padiscubapro referred to:

http://www.pstscuba.com/tech.htm

I always tape a copy to the cylinder when I drop my cylinders off for testing...

Roak

[padiscubapro]

roakey once bubbled...
Here's the procedure that padiscubapro referred to:

http://www.pstscuba.com/tech.htm

I always tape a copy to the cylinder when I drop my cylinders off for testing...

Roak

Thanks Roakey!

[Genesis]

when it comes time for a Hydro I won't do it at a LDS - I'll find a certified place locally and take them there myself.

There's no reason to pay the markup on this one at all.

[padiscubapro]

Genesis once bubbled...
when it comes time for a Hydro I won't do it at a LDS - I'll find a certified place locally and take them there myself.

There's no reason to pay the markup on this one at all.

Just be sure of the procedures involved.. most hydro facilities are used to doing things like fire extinguishers and industrial cylinders.. You will also probably have to tumble and definately clean the cylinder after getting it hydrod (this is usually done by your LDS). Scuba cylinders are usuallly a small percentage of their hydros(and mnay use the same water over and over and over again)... and I bet many have never seen PST cylinders...

[Genesis]

I know.... fire extinguishers are probably their most common...

:)

[GDI]

:doctor:
I get the cracks about diving dbl HP 120's in cave country all the time as well. It's no biggie since my air consumption is usually better than most, and I have yet to turn a dive based on my air supply. If doing Deco I will use a combination of Al 80's and Al 40's, generally as the travel gas leaving the back gas in the HP 120. And when diving trimix the issue of gas compressability has never really been much of a concern. I can make adjustments on the amount of He I need as far as what my LP 104 buddies use. My bouyancy is not hard to achieve using either LP104 or my HP 120's. I do have them mounted so that they are not banging my butt or bumping my head. Maybe I am at just the right height. If you want to overpressure a cylinder than thats up to you. Most places that I know have no problem giving me the fill that my cylinders are rated for. Some shops simply have a policy not to fill past 3000 or the cylinders working pressure. As for diving with my HP 120's well they do just fine for me and I'm not carry the weight

[BlueDolphin]

WYDT....

Are you saying that HP tanks or overfilled LP tanks are harder on the hoses, and 2nd stages? I would have thought the first stage would have reduced the pressures reaching those?