LP 85 Vs. HP 100 Doubles, Advice Please.

[tangfish]

Hello, I am currently diving Twin HP 80s and I enjoy them. I do notice that I have a tendency to roll onto my back, I'm not sure if this is the case with all doubles. I don't have a faceplanting issue as some warned I might have, hopefully because i followed some good advice here at SB and mounted the bands as high as possible on the tanks.

I am buying another pair of tanks for doubles (need more BT). I am trying to decide between LP 85s and HP 100s. The 100s run about 90 bucks more per tank and are a couple inches shorter.

Now, here are the things I am considering:

100s:
pos - smaller, more air at recommended psi
neg - cost. hard to find good fills away from my LDS?

85s:
pos - easier to fill and can overfill to almost the same cu ft. as the HP 100s
neg - larger

I need some advice and info. I've been told by a couple people (and everyone else disagrees) that the + rating on the LPs means that they're 85 cu ft when they're overfilled by 10%. This is counterintuitive to me and results in less of a direct comparison in terms of amount of air when overfilled. The HPs cannot be overfilled as much so don't gain as much air from that (3442 - approx 3800). The LPs, if they are indeed 85 cu ft @ 2400 psi are usually filled to around 3000 - 3200, which is a huge gain, and results in almost as much air as the 100s.

Does anyone know the answer as to whether or not the 2400 is actually 85 cu ft?

Also, someone was telling me that the extra couple inches might actually be a good thing, so that I have more tank to spread across my body, making the twins more stable. Is this true or is that much difference in height negligible?

Do you folks really have that much trouble getting good fills on HP tanks when traveling regionally? I've heard about some bad fills, but maybe that's just because you hear the worst stories. The price of the HPs is pretty steep, can you think of any justification for spending 90 bucks more per tank? I like the small size of my 80s and the 100s aren't that much bigger but it's a significant amount of gain in air, which is what draws me toward that option.

Any additional considerations or advice are welcome, but I'd appreciate it if only people who have experience diving doubles would offer the advice (i.e., please don't give me advice you heard somewhere else but haven't verified yourself).

Thanks in advance for helping me out.

 

[cool_hardware52]

Any tank with a + rating will hold it's rated capacity only when filled 10% above the marked fill pressure. The LP 85's will hold 85 cuft when filled to 2640 psi, not 2400.

I simply prefer LP tanks. Easier to get full fills, and if you are PP blending Nitrox the required PSI of O2 for a given mix will be lower.

I have a couple sets of lp85's doubled up, and I enjoy diving them.

If the dives you aspire to require 200 cuft of gas get the 100's, if not I'd get the 85's


Tobin

 

[CD_in_Chitown]

Any tank with a + rating will hold it's rated capacity only when filled 10% above the marked fill pressure. The LP 85's will hold 85 cuft when filled to 2640 psi, not 2400.

That's not exactly the case is it? I thought 2640 was the rated fill and + meant 10% on top of that for the extra volume?

IME 85s and 100s dive really similar, both are my preference in doubles. I don't think you can go wrong with either. But that's not the "what kind of dives are you doing" answer. I haven't found many dives I can't do in my 100s, well that I am qualified to do and all I mean.

 

[tangfish]

CD, the 85s are rated to 2400 psi, with a + rating. So, 2400 X 1.10 = 2640.

The question Tobin was answering was whether the tank has 85 cu ft at 2400 or 2640, which he answered for me. Still, if you fill that tank to 3200 that is still 560 extra psi which is slightly more than 20% more air, so 85 X 1.20 = 97 cu ft. That's getting close to the 100s, when filled to 3442.

Tobin, thanks for the advice on the Nitrox, and to answer your question, I'm not aspiring to any types of dives in particular. One thing I'd like to do is to get closer to my buddy's amount of air. Even though I breathe quite a bit less than him, he is currently diving LP 98s and my HP 80s run out sooner. So, I was thinking that if I get larger tanks then it would be more even and perhaps more stable (I keep reading that the longer the tanks, the more stable the rig becomes). BTW, I'm 5'8" ~ 170, in case that paints a better picture.

Looks like there isn't an overwhelming reason one way or another. I'm glad I found out about the + thing though, since that means the 100s do have a fair bit larger capacity than the 85s.

Thanks so far, and keep the advice coming

 

[Hoyden]

I have gone through several sets of doubles in my search for the "ideal" tanks. I have owned and used Catalina AL 80s, Faber MP 72s, PST HP80s, PST HP100s, Faber HP100s, Faber LP85s and Faber LP95s. I started with the AL 80s and hated to have to carry extra weight so I got the Faber 72s and PST 80s - of those two, I loved the 72s, I just needed more gas. They were small, negative and very nice for climbing boat ladders. So they gave way to the HP 100s - had a set of PST HP100s and got a chance to buy a set of Faber HP100s cheap. The Fabers trimmed out much better, but they were a little heavy for me. After a FL trip where I never ended up with a fill above 3000 psi, I decided to go LP and got a set of 85s and a set of 95s. The 85s are just about perfect. They trim out well, swim easily and are a very nice weight. They are a larger volumn tank and hold more gas at a given pressure than HP 100s. Faber LP85s hold 793 cubic inches of water - PST HP100s hold 777 cubic inches of water. What this means to divers is that at 2000 psi a single LP85 holds 65 cubic feet of gas and a HP100 holds 57 cubic feet. At 3000 psi, a LP85 has 97 cubic feet of gas and a HP100 has 86 cubic feet of gas. If you always get full fills on your HP tanks then choose the ones that trim out and swim better. It was my experience that I rarely got full fills on my HP tanks. I tried to attatch an Excel chart that I use to help me keep track of the tank volumns, but I couldn't get it to upload. I'd be happy to send a copy if you pm me your email address.

YMMV,
Jackie

 

[tangfish]

Wow Jackie, this is the more help than I ever imagined I'd be able to find on this subject. Sending PM now. Thanks!!!

 

[The Kraken]

Funky, you've put me into a funk now, too !!!!

Recently I've been considering some dedicated doubles.

My quandry is whether to buy 2 manifolded 100's or buy a 4th E8-119 and double up the E8-119's.

Decisions, decisions, decisions . . . . !!!! Oh, my !!! What is a diver to do ????

the K

 

[tangfish]

The Kraken (btw, The Clash of the Titans is an awesome flick), you're right that this is a hard decision. For me it's simpler because I already have the manifold and bands to fit only a 7.25" tank, so I can't go to a larger tank unless I want to buy all the rest too.

I'd say, all other things being equal: how much can you carry?!

I'm already pretty well exerted carrying around my (puny) E7 80s, I can't imagine a long walk to the dive site with some 119s. Also, what are your buddies diving? It never hurts to have a setup that is complimentary to those who you're diving with.

 

[The Kraken]

Most of them have 95's, that's why I'm leaning toward the 100's.

In spite of my advanced years, I can still pretty much carry my own weight and some more.

The 100's would allow me to keep my 119's as my favorite singles.

Ya can never have too much back gas. Even though most of my buddies dive with considerably less gas, I like the concept of having extra if someone needs its. Once one gets in the water it's all academic anyway.

the K

 

[JimC]

TFor me it's simpler because I already have the manifold and bands to fit only a 7.25" tank, so I can't go to a larger tank unless I want to buy all the rest too.

Don't most bands set the tank centres in the same place so you can use the manifold with any set? I know mine do. My 72's and 130's use the same manifolds.