LP 85 vs HP 100

[jc2]

I'm diving with a Diverite Trek Wing. When I start diving doubles I was going to go with OMS LP 85 tanks, probably slightly overfilling to about 2,800 psi. However I'm now thinking about going with HP 100's and underfilling them to about 3,100 psi and getting about the same air volume as I would overfilling the LP 85's and while putting less stress on the regulator. The reason is that the tanks are a couple inches shorter and would therefore maybe be a better match for the trek wing. Diameter is 7.25" versus 7.0" for the OMS LP 85's. More importantly I figure using the HP 100's, I'd have more versatility, so for instance if I had to do a shore dive with a long walk or walk down rocks, I could go with a single tank and could fill to the full 3,500 psi and have quite a bit of air. The weight and boyancy characteristics are very similar between the two.

I've heard that HP tanks though typically have a lot more chance of failure than the LP tanks but I think I would overcome this by underfilling it 90% of the time?

 

[spectrum]

First, where do you get the assumption of filling LP85s to 2800 PSI? I know in some areas this transgression is common practice and if you have a compressor... well the sky's the limit. Otherwise they are LP85s as long as long as the + rating lasts.

On the HP100s how is a fill to 3100 going to put less stess on a regulator than one to 2800? Pressure is pressure and while there is a difference both are within design limits as is 3442 with negligible effects. This assumes reasonably modern gear.

If you can afford the HP-100s they are a more elegant solution. the only downside (asside from cost) is the occasional shop that can't or won't provide an optimal fill but even then you are almost certain to walk out with better than 85 CF. The HP cylinders probably have a somewhat higher chance of failing the hydros than the imortal LP cylinders but I don't see that as a criteria for chosing something less than the optimal configuration. If you don't get the HPs overfilled you probably mitigate most of the risk. The risk is of failing hydro, not rupture.

FWIW we're diving PST E7-80s and PST HP-100s

Pete

 

[jc2]

Regarding underfilling the HP 100's to put less stress on the reg, I meant less stress relative to filling the HP 100 to the full 3,500 psi. Obviously 3,100 psi is going to be more stress on the reg than 2,800 psi in the overfilled LP tank. I'm just looking for a good compromise between maximum air volume and least amount of headaches with things like difficulty with getting the fill pressure you want (I've heard it can be difficult to find a place that will give you a full 3,500 psi), least potential for equipment problems, etc., etc.

In reading one of the other threads a consideration I forgot to include is trim. I'm 5'-11". It seems many people my height prefer the longer tanks in this respect, but then they probably aren't diving a short DR Trek wing either.

I found a lot of good information about tank configurations on the New Jersey Scuba Diver website. While there seems to be a lot of 'opinions' regarding SCUBA gear setups as everyone seems to want to preach their own mantras and personal preferences, this article seems to be a fairly level-headed piece of information. http://www.njscuba.net/gear/eqpt_05_tanks.html It acknowledges DIR guidelines but also points out the most important thing is that tank configuration really has to do with the type of diving.

With me, some days I may have a long walk for a shore dive and may not be going below 60 feet so I just want to dive a single tank other times I may be doing a boat dive in the San Juans and may be diving a lot deeper and don't want to be air limited as far as the length of my dive. I know optimally I should have a wing for singles, a wing for doubles, a doubles setup with manifold and a couple other tanks for singles, but I don't dive often enough to justify the cost of all that.

The statement that really hit home with me on the New Jersey Scuba site was "What I am recommending is the ability to flexibly configure your equipment for whatever type of dive you are doing right now - whether it be deep, shallow, long, short, boat, shore, currents, waves, etc. The discussion of temporary doubles bands is motivated by the fact that manifolded doubles are anything but flexible ( and are also ridiculously expensive ) and that it is relatively rare to actually need double tanks for a particular dive. "

In most cases I'm either going to be diving a single or when I want more bottom time, I'm going to be diving doubles and I like the one-and-a-half scenario where I'll have a third tank I'll swap in for my second dive. I really like the flexibility of having independent doubles instead of using the manifold although I know the manifold configuration is more popular with most people here. I'm not doing wreck penetration dives or cave dives or tri-mix or anything that technical. Mostly rec dives with an ocassional deep dive. Plus with the independent setup, if I don't want to spend a bunch of money on tanks to begin with, I could just go rent some ALU 80's and put up with the less optimal boyancy characteristics.

I guess I've spawned this discussion into two issues, best tanks for my applications, and manifold versus independent but I purposely didn't bring the manifold vs independent issue up initially as I figured it's one of those subjects that has been beaten to death here many times before.

 

[Tom Winters]

I love my LP85s and flat out do not like HP tanks. My wife LOVES her HP100 tanks and will not use anything else. She looks at my LP fondness as some psychological aberration, but I have learned to accept her unbalanced views.

 

[jc2]

Leisurepro has the LP 85's with Thermo PRO valves on sale right now for $169. That seems like a great deal, almost half the cost of the HP 100's. I think my decision may boil down to economics with that big of a price difference. At least with the LP's I won't have to worry about getting the thing filled to capacity.

 

[onfloat]

At least with the LP's I won't have to worry about getting the thing filled to capacity.

Wanna bet???

 

[cummings66]

I would say that if economics drives your tank decision then buying a LP85 makes perfect sense for you.

However you don't say if you have good air consumption rates or not, that should also be part of your decision, there's nothing worse than having your dive cut in half by a boat buddy who sucks his air down. The HP 100 will give you more air and weight a couple lbs less than that site indicated, but who knows what they mean by a good fill anyhow. At worst it's 3 lbs heavier but still gives you much more air.

Both are good tanks in my book, I'd opt for the HP 100 due to longer bottom times on Nitrox, also on normal air if you use rock bottom limits. I can hit the NDL on an AL80 and have enough air for me to return to the surface, but if I consider my buddy's air usage which I do then I need to come up before I hit the NDL.

In other words, how many cubic feet of air do you have left in a dive to 100 feet at say 20 minutes? Do consider this in choosing what volume tank you get.

 

[cummings66]

Wanna bet???

Just out of curiosity, what issues would you have in getting a rated fill? If they can give an AL80 it's rated fill there's no reason that they can't do the same here with this tank. I do not know of a single dive shop around here that would have that problem.

Now on an HP tank that gets up to 3500 psi I have problems getting a full fill if I want my tanks back quickly, and I routinely accept tanks that are lower than rated. I bought larger tanks just because I knew that would happen and I still have more air than an AL80 on every single dive. In other words I routinely get 3250 - 3400 psi fills at most dive shops.

 

[onfloat]

Just saw this,
It's not usually a problem of the compressor being able to deliver the required pressure, but the monkey filling the tank. They see it's a low pressure tank and give you a short fill. In the 2 years I have had more 2300 psi (about 300 short with the plus rating) fills than I can count. Of course there have been a couple of times when it was filled to 3200, too.