Difference between HP and LP Steel tanks

[jgarysmith]

Someone please give me the differences and pros and cons of HP and LP tanks. I purchased a HP 100 tank and after reading some posts am wodering if I made the right choice. I am diving Nitrox with it, and my main concern is bottom time. Explain the difference of a lp steel tank that has 2400 PSI ratings and a hp steel tank that has 3500 psi ratings. Any help or oponions would be appreciated.

 

[Mo2vation]

Someone please give me the differences and pros and cons of HP and LP tanks. I purchased a HP 100 tank and after reading some posts am wodering if I made the right choice. I am diving Nitrox with it, and my main concern is bottom time. Explain the difference of a lp steel tank that has 2400 PSI ratings and a hp steel tank that has 3500 psi ratings. Any help or oponions would be appreciated.

Just so you know, the search function will deliver to you dozens of threads dealing with this subject. As somone who just moved from an HP100, and having completed many weeks of research on this very subject, I can offer the following:

1) HP tanks have great curb appeal. Smaller, lighter, favorable buoyancy, etc.

2) If you dive where you can consistently get a 3500 fill (I mean, when its cool, its 3500) then you're in great shape. For me, I dive mostly off of boats. After looking at a year in my log, I found I got one 3500 dive (my first) and the rest were about 2600 - 2800, maybe 3000.

3) With short fills, I was diving with 77 Cu ft to 90 Cu ft for 2/3rds of all my dives. Only the shop-provided 3500 fill gave me 100 Cu Ft.

I wanted more BT - so I moved to a big LP tank. Its bigger. Its heavier. But I get a little over 100 Cu Ft at 2700, and a lot more gas at 3500. If you're able to get real 3500 fills, you'll get your 100's worth.

I LOVE my HP100. I still have it. Its now my wife's cylinder and I eBayed her tiny HP80. Its a fine tank (presume PST...?) and you'll love it. The thing is watch that you get fat fills or else you're not leveraging the beauty of the thing: 100 Cu Ft of gas in its small, managable size.

Do a search. We've hit this subject a number of times.

Welcome to the board!

K

 

[scubasean]

Someone please give me the differences and pros and cons of HP and LP tanks. I purchased a HP 100 tank and after reading some posts am wodering if I made the right choice. I am diving Nitrox with it, and my main concern is bottom time. Explain the difference of a lp steel tank that has 2400 PSI ratings and a hp steel tank that has 3500 psi ratings. Any help or oponions would be appreciated.

Assuming that both are 100 cf tanks, the primary differences are the out of water weight [the lp tank is heavier] and the in-water buoyancy characteristics(how much weight you wear on your belt; you will generally wear more with the hp tank).

I wear the HP E7-100 and have gotten a 3500 psi fill all but twice, out of 45 dives using it.

 

[jgarysmith]

Thanks for the reply K. I get my fils at a LDS at the have been filling 3500. Main reason I bought it from them. I also boat dive here inVA BCh, VA, but I get my tanks filled before boarding. I plan on purchasing another to take both. Thanks for all your advice. I have read alot of your replies. The board is a great place to get info. G

 

[jgarysmith]

Thanks Scuba sean for the reply. I seem to be getting 3500 fills most of the time. G

 

[LUBOLD8431]

Well, with the new PST E series cylinders, it kinda makes this topic a moot point. They are all rated at 3442 psi. The only difference being diameter (7.25 vs 8 inch) and weight (the E8's which replaced the old Low Pressure are heavier)...
If you are going with Faber steel cylinders, then may the Lord be with you...
kidding... Faber cylinders are weird. The HP ones are heavier than the PST counterparts, and the LP are a little lighter than the PST counterparts...

Its best to get a spec sheet from both companies and compare. Or, just go with a cylinder that will compliment the type of diving you are doing...

 

[DepartureDiver]

If you can get your HP tank filled, then there are no issues. Some boats can't fill them full and so you dive short. The only other issue is if you ever get into tech diving, especially with trimix (which you would need another one to set up doubles). Blending these gasses is easier with LP tanks. While I prefer LP tanks, I think it is personal preferance and you should enjoy your tank without any second thoughts.

 

[LUBOLD8431]

The only other issue is if you ever get into tech diving, especially with trimix (which you would need another one to set up doubles). Blending these gasses is easier with LP tanks.

This is not exactly true. While a higher pressure allows more heat to build up, it really doesnt make it harder. HP tanks are becoming alot more popular now, and in the case with PST, the only option. As a certified gas blender, and having filled quite a few tanks over the last few years, I can say that it really doesnt make as much difference as alot of people think. HP tanks just need to be cooled off more than LP tanks. Unless you have a home fill station, you're not doing the mixing anyways...

 

[DepartureDiver]

I have to disagree with you. While it may not be true at every fill station, it will be true at a lot. It is not a heat issue, it is a fill issue. For example, if a HP cylinder is brought to you with 2500 psi in it and you need to add oxygen to it to reach your mix, the fill station will require a booster pump (since the cascade tanks come in at less than 2500 psi). I am very uncomfortable boosting O2 at that pressure. The other option is to drain a tank so that the O2 can be added. Also, if the tank simply needed helium added, again a booster may be required (which many, but not all fill stations have) to put helium on top of an already pressurized tank. A set of twins better not be coming back low or the diver did not reserve enough gas for an emergency. It would be common and proper dive planning for tanks to be coming in half-full for their next blend and mix. So the issue is the ability to add the necessary gas on top of a half-full tank of 1750 psi. Assuming the fill station has a helium analyzer, oxygen would have to be added to the 1750 and the helium on top of that. It may not be an issue with your fill station, but it will be with some. None of the dive stores in my area have a booster pump ... which is why we footed the massive cost to build our own station (which I know is far from the norm) with a compressor and booster pump ... and I still know how long it takes us to do the fills with a booster pump to get an accurate mix for the 400' dives we are doing. Hopefully booster pumps will become the norm soon.

 

[LUBOLD8431]

Well, I feel sorry for any shop that is filling cylinders with mix without a booster. I thought they were the norm...

Maybe its just where you live, because everywhere else Ive been has them...