LP vs HP Tanks

[rstofer]

No, I don't think I am trolling. I want to frame this question very carefully because I will never overfill a tank. That's the baseline for this question: Legal fills only!

I have always thought that there was no purpose to LP tanks other than, perhaps, to accommodate double hose regulators. I'm probably wrong but it seems to me that LP tanks are generally heavier, certainly larger for a given capacity and with different buoyancy characteristics than an HP tank.

No doubt, I am wrong in my opinion. I do know, for example, that I will never get a complete fill of a 3442 psi tank on a dive boat.

What other advantages does the LP tank have over the HP? There must be some reasons that they are still made. People must be buying them and they can't all be going to Florida.

I have just one LP tank, an older 72, that I like to use in the pool. What a terrific tank! But there is no point in using it in cold water because it is too buoyant compared to almost any HP tank. Still, with a J valve and a double hose regulator, it is a neat setup!

Any thoughts? There must be something I am missing and I really want to know.

Richard

 

[reticentDiver]

The only thing I can think of is what you have already suggested: some dive shops may not be able to fill up an HP tank to its maximum allowed pressure because they are using older equipment. I'd be interested in what other people have to say, I've been wondering about this myself!

 

[Teamcasa]

Tanks are such a personal thing. LP tanks (as you said) work well for getting full fills on dive boats and AL80's do seem to be the go to tank for rental operations. Everyone has their reason to justify the tanks they have and use. I like my HP100 but have a couple of AL80's that virtually never see any use.

 

[ptyx]

• LP: easier on the shop and on the gear (first stage)
• HP: easier on the back (at least for cold water diving)

That sums it up for me - back wins.

 

[bamamedic]

LP cylinders are generally a bit less expensive than HP cylinders...

 

[Nemrod]

LP because some of us do overfill and that is why we like them.

Balance better and trim better in many cases as well.

N

 

[dannobee]

Why is this an either or proposition? Tanks are not mutually exclusive.

LP tanks for boat diving and doubles when "good" fills are available.

HP tanks when high pressure fills are available or you don't mind short fills.

I have so many tanks at home that it really doesn't matter one way or another.

I guess it does. I'll take the ones with gas in them and go diving.

 

[spectrum]

By removing the desire for overfills and being short fill tollerant you short circuit a lot of the typical discussion.

HP cylinders are most efficient package in terms of buopyancy properties and total diver weight. If you are tolerant of some short fills then they work very well. I dive almost exclusively HP with single and double hose.

LP cylinders are less expensive and proportionally taller for the same CF capacity. Many taller divers have a hard time with an HP 80 and it usually takes a short diver to enjoy them as doubles. The mass of the short tanks is so concentrated that stable trim is hard to attain for some divers.

There is some anecdotal information that siggest the HP cylinders are more prone to corrosion and fickle at hydro time.

There is an underlying mentality with regard to dive gear. If you own it and it got you home safely it must be the best. Some people simply are not big on adopting new technology and there is no real logic in the decision. At the end of the day for 90% of the divers 90% of the time any cylinder with the CF capacity will serve the purpose. Some divers do try to optimize their choice in some way but there are always trade-offs.

Pete

 

[Gombessa]

I understand there used to be a greater delta in price between LP and HP tanks; nowadays an HP100 is about $80-100 more than an LP80, which is meaningful to some people but not enough to matter to others.

If you're comparing rated capacity, sometimes the LP tanks provide favorable buoyancy and trim characteristics to HP tanks--a lot of people have trouble trimming out well in HP80s, but LP80s are simply great.

If you're comparing dimensions, a lot of us consider LP80s and HP100s as functionally equivalent. I won't dwell on the dreaded O-F word, but if you can get them, why pay extra for HP? At the same time, an underfill on an HP100 is still typically 80+cf, which is fine for most dives.

Just get what best suits your needs and conditions.

 

[Scott L]

There is far less reason to select LP cylinders now then in the recent past. The comments below are from Fill-Express, a leading Tec shop in Ft Lauderdale Florida. Also, Extreme Exposure's go to cave cylinder is the Worthington X8 HP.


What Happened to Low-Pressure Cylinders?
Many experienced divers have preferred low-pressure cylinders because they are easier on regulators, have no short-fill concerns, and are more suitable for partial-pressure blending. More recently, the low-pressure 3AA cylinders (2640 psi, i.e., 2400 with a +) are being replaced by the new DOT exemption cylinders (3442 psi, no plus needed). That's because you can use the high-pressure 3442 psi cylinders as low-pressure 2650 psi cylinders if you prefer, simply by under filling. The 3442 psi DOT Exemption cylinders have the same length, diameter, and capacity at lower 2640 psi pressure as the 3AA cylinders. Even better, the empty weight of the new cylinder design has been reduced slightly, yet the buoyancy remains slightly negative when empty.