wa123

I read here quite often about LP steel tanks.  I understand the weighting advantage of steel, but why LP instead of HP ? If you're going to use steel why not fill 'er up ?  Around here we see mostly AL tanks with a few HP's here and there.  Ocassionally you'll see an Old 72. D.C.C.

I read here quite often about LP steel tanks.  I understand the weighting advantage of steel, but why LP instead of HP ? If you're going to use steel why not fill 'er up ?  Around here we see mostly AL tanks with a few HP's here and there.  Ocassionally you'll see an Old 72. LP tanks can be overfilled, HP cannot.   For those who are doing trimix fills at home (or the shop), it's better when you only have to fill the tank to X% of 2400 instead of 3500 - you get more fills out of your helium source.   LP is lower stress on the gear. Main downside is they weight a hell of a lot more out of the water - more mass in the water.  

Main downside is they weight a hell of a lot more out of the water - more mass in the water.   One of these days I'm going to buy an LP104/HP140 And I'm going to paint Goodyear on the side.  

I read here quite often about LP steel tanks.  I understand the weighting advantage of steel, but why LP instead of HP ? If you're going to use steel why not fill 'er up ?  Around here we see mostly AL tanks with a few HP's here and there.  Ocassionally you'll see an Old 72. D.C.C. Bang for the buck. HP steel relies on internal pressure to obtain rated volume. LP steel relies on internal volume to obtain rated volume E.G. HP-100 internal volume  779    LP-104 internal volume 1034 For every 14.7 psi you overfill, there is a 255 cuIn advantage (roughly) for LP. Above 3000 psi or so, depending on gas, compressibility falls off rapidly, further reducing the bang for the buck on HP, if overfilling is considered. For equal capacities like this, the extra volume does not come free. The LP-104 is a monster:   The LP-104 weighs 46.4 lb.   27 x 8   The HP-100 weighs 34.1 lb.   24 x 7.25 Overfilled or not, LP tanks are easier to partial pressure blend. Overfilling LP is not a 'given', unless you have your own compressor. It is relatively safe, but not all shops will do it, and if you do, you should change out the burst disk for a higher rating. You still want to put them in your trunk, and bake them up without losing the load. Overfilling LP or HP will probably reduce ultimate life. They will probably fail Hydro sooner...FL is trying (or already has) to impose some kind of law that mandates tank replacement after 15 years. If so then the hydro life issue is moot... Around these parts, some shops will overfill LP steel and some will not. Some will also overfill HP to 3.8-4k. It just depends. Know your shop, keep your tanks clean and shiny, and let your fill shop do the inspections they want (let your shop know your tanks). If you are considering steel for recreational, I think there are only two choices:   The PST HP-100 or the PST LP-80. Both are about the same size and weight as an AL80. Both will balance better and be about neutral when empty, removing 4 lbs off your belt. Faber also makes a small LP, that weighs in at about 32 lbs. Scubalux called it the 'LP-78'...if keeping on fair terms with PST capacities, it should be called 'LP-74'. Keeping recreational no-decompression limits in mind it is wasteful to have tons and tons of gas you don't need. What you want is the tank that gets you to NDL's without running low. If you dive Nitrox, that's naturally a bigger tank. The advantage of the LP-80, is that even at lower pressures it still has the gas of an AL80 but has reduced the weight on your belt and improved your trim. If over filled to 3000 with air, it will have about 94 cuFt. That's a nice extra margin when you need it. It also will have a Yoke valve by default, so your regs won't need adapters when you travel. The advantage of the HP-100 is that it has all the gas you need for any dive. It has an extra margin that heavy breathers need and others want for comfort. However, the Fabers are as much as 30% cheaper than PST's. Alas, the Faber HP's are very heavy. I don't know why. But they are too heavy for me to even consider. There is a popular urban myth about HP/LP steel tanks. It goes something like this: US LP tanks are the same as Euro HP tanks ... Somebody will probably repeat it in this thread, if they haven't already. For a dose of truth, take a look at:     http://www.divefaber.com/light/scubafra.htm ...click on 'dive cylinders', then 'catalogue', then '11.96 < 14.5' You'll see that Faber (a euro company) makes over 40 models of 12L cylinders that vary in weight from 11.2kg to 18.6kg, that's a 16 lb difference and guess which end of the range the 300 bar cylinders (HP) are at. 40 models of 12L cylinders! That should tell you something right there. The lightest HP cylinder you can find will be almost 17 kilos, and the heaviest LP (I couldn't find a LP 12 liter, so we'll go 200 bar/2900 psi) is just under 13 kilos. That's almost 9 lbs of chrome/moly steel and I guarantee you that Faber doesn't put it there for fun.

There is a popular urban myth about HP/LP steel tanks. It goes something like this: US LP tanks are the same as Euro HP tanks ... Somebody will probably repeat it in this thread, if they haven't already. I enjoyed your post, but can you explain why someone would and would not believe the above statement? Thanks Chris