When would you choose HP over LP

[shockere85]

I am actually wondering when would you use each, and if you are answering what do you prefer for cold water diving.

[fisheater]

I prefer my HP120s, as they give me more air than an LP version of similar size.

[DMWiz]

Some people prefer LP tanks because they are almost always guaranteed a full fill (or overfill) while others feel that if the compressor cannot pump over 3000 psi the HP tanks are not getting fully filled. (I have never had that issue) I guess some older compressors or boat compressors have this problem.

I personally like HP tanks not because of the fill pressure difference, but because of buoyancy characteristics and size of the tanks I use.

[Rainer]

Let's break this down.

HP Pros
-Holds more gas than an LP in an equivalently sized cylinder IF both are filled to rated capacity (for similar capacity, this means a smaller HP cylinder).
-Can use to transfill to an LP cylinder (especially useful with large capacity HPs).
-A high capacity HP is still a lot of gas even if under-filled (e.g. HP100 at 3000 still beats an AL80).

LP Pros
-Easier to obtain a full fill (many compressors cannot go to 3500psi).
-Easier to do PP blending (matters if you plan to do your own mixing).
-Can use to transfill into from HP cylinder.
-Cheaper than HPs (used to be significant, now less so).
-If shop is willing to overfill, then you just bought HP at LP prices.


I have a mix of both for cold water diving (LP85s, HP100s, HP130s, plus plenty of ALs). The choice is dependent on what matters to you (cost, size, importance of mixing at home, etc) and what your local filling situation is like (availability of over-fills, type of blending, etc).

[CompuDude]

Rainer pretty much hit it. I prefer HP tanks, because many places (around here) will not knowingly overfill an LP tank. I'd rather they at least attempt to hit the 3442 (or whatever) limit than stop at 2400/2640. I also really dislike the Plus rating system... every 5 years, when you hydro your tank, it must be done by a facility that is (a) capable and (b) willing to do a proper certification to confirm the Plus rating of an LP tank. Otherwise the LP85 you just purchased (which holds 85cf of gas when the Plus rating is current and can thus be filled to 2640 instead of the regular 2400 psi level) is now technically only allowed to be filled to 2400 psi, which leaves you with 77cf of allowable capacity. That's not what I buy steel tanks for. I'd rather have the HP100, where I may or may not get the full 100cf of gas, but at least there's no chance someone will stick me with a 2400psi fill because I couldn't find a hydro facility that Plus certifies my tank. (They're not easy to come by in all areas.)

[MSilvia]

Good answers. I use both for cold water. Currently HP100 doubles with LP72 singles, but I'm about to switch that to LP72 doubles and HP100 singles.

[skdvr]

I only have HP's... The shop that I mainly go to would overfill LP if you ask for it, so I would not object to LP tanks. If buy a LP tank with the idea that you are going to get the rated fill out of it, and then if you can get overfills then BONUS. Otherwise I say buy HP and if you want you can underfill them if you want.

Just for instance I have one HP 130, the LP equilivant is the LP 108. They are roughly the same size. You can underfill the 130 anytime that you like to get around 100cf. But if you can get overfills the LP 108 actually gives you a bit more gas.

LP108 @ 3500psi = 142cf of gas
HP130 @3500psi = 132cf of gas

If I found a good deal on LP tanks I would not pass them up, but me personally if I am buying new I am getting HP, just because around here it is easier to get the good fill without having to hope someone will overfill for me...

Phil

[in_cavediver]

I have entirely LP steels. Didn't really plan it that way and I did have an HP 120 at one point. Its just what was cost effective and works.

My 104's came before the advent of the HP130. Not really a choice there
My 85's (all 4) came at prices as a pair that was on par for a single HP 100
My 45's were deliberate - for transfilling O2. Again, they came cheap - 400 for a pair with manifold and bands.
My 72's were free. Can't argue with that.

As for overfills - generally, my tanks get DOT fills for local dives and cave fills for cave dives (or deep dives). I've never had a problem with getting fills I wanted. Though one day I was at vortex and they asked how much I wanted in the 104s and I said 3600 - they laughed and said they fill it so long as I stood by it. It made 3400 when he shut it down. (equalized the bank on it)

[digital_steve]

I got 300bar tanks (i suppose what you guys call HP) for my twin 7's setup because of their buoyancy characteristics. It means less weight on the belt for me and less faffing about with pockets/weightbelt at a divesite

[Rainer]

The buoyancy characteristics for the HP and LP steel cylinders (at least most of the newer ones) are the SAME.