Is HP actually bad for regs or is this a non-issue

[dlwalke]

I had more or less decided to get my own tanks and was going to go the LP Steel route. Not an imminent purchase, but within the year probably. I feel like I need a shorter tank than the usual AL80s that I rent, but want to stay at around 80 cubic ft. I would like to get something around 22 inches (w/o stem) as I believe the AL80s are mostly 26 inches and I would like to leave 4 inches). However, thus far on the web I have not been able to find anything that fits the bill. Closest I've seen are the OMS 80 cubic inch tanks that are 24". So I am now wondering if I should reconsider HP tanks. Do they actually cause premature regulator death? Thats the main knock against them that I have heard. How true is it that they stress your equipment too much.

Also, on one of the spec tables I saw, I noted that there were a variety of working pressures for different cylinders. When does LP become HP. I had thought that this was more of a dichotomy whereas, unless I misunderstood the table, I now think it is more of a continuum.

Thanks,
Dave

 

[sheck33]

The reason i personally switched from HP tanks to LP ones is not really the stress on the whole system but rather for the following 2 reasons:

LP tanks are obviously easier to fill, so the chance of a short fill is less if the LDS is in a hurry to fill tanks.

The second reason is that, if you do overfill them (which of course is also easier on a LP tank), you will get relatively more air for the same overfill.

The higher the pressure the less a gas acts as an ideal gas.

So, personally i would go for LP tanks.

As to where exactly the line LP to HP is located i am not sure.
My tank working pressures are in the 2240 - 2400 PSI range

 

[The Chairman]

In fact PST has discontinued their LP line in favor of 232 bar tanks. However, the current design and materials used in modern regulators have no problem handling these higher pressures. Just make sure you have them serviced once a year.

 

[Braunbehrens]

Why do you want such a short tank? Just curious.

I have dived PST HP 80, PST HP100, PST LP104, and a number of 80's both AL and steel. By far the nicest tank is the PST 104, but that's a big heavy tank.

The HP80 is an ok tank, as a single, but you should really look at it in terms of acutal volume, not how much gas it holds at it's rated pressure. Otherwise you may be surprised when you find out that 500 psi in that tank goes quite a bit faster than in a LP100. Also, the HP tanks have a tendency to drop a lot of PSI's in the first few minutes of the dive. This is a combination of smaller tank volume, warmer fill pressure, higher cool-down effect, and possibly real vs. ideal gas laws. It's also harder to get an exact trimix fill in a HP tank, although an experienced mixer should be able to do it.

I don't agree with the idea that HP tanks are inherently harder on regs. Many people overfill LP tanks, so the pressure really is the same, and if you don't want to fill the HP tank to 3850 psi just tell the guy at the shop to fill it to 2800.

What's much more important is how the tank dives, and how it affects your trim. For that, the HP tanks are pretty bad, except maybe for the PST HP120.

PST just changed all it's tanks around, so I have no idea what the new stuff dives like.

 

[dlwalke]

Why do you want such a short tank? Just curious.

I am a bit short (5'6-1/2", and I think my torso is even shorter than that would suggest. I just feel that the standard AL80 is too long for me. If it is moved down far enough so that the valve is not banging me in the head, then the bottom of the tank is pretty darned low. I guess its not such a big deal underwater, but if I get my own tanks I would prefer to get something that is ergonomically more manageable for me.

I didn't realize that there would be that much difference in how tanks "swim". I had thought that you could mostly offset any problems with trim, for example, by moving some of your weights to your ankles or tank valve. In any event, I am definitely hoping to rent a couple of different length tanks prior to making a purchase. I haven't inquired about this, but am hoping that I can find a shop that has something other than the "standard" AL80 to rent.

Dave

 

[Bob3]

There is a lot to be said in favor of shorter tanks, if you don't mind shelling out the extra bucks a set of stubby doubles has such sweet balance that you might pee yourself.
There are a lot of different combinations out there, my own personal taste leans towards steel but there isn't anything inherintly "evil" about aluminum.
A pair of 40s or maybe even 63s should fix you up just dandy.
If you're into scrounging, twin post non-isolation manifolds are becoming more available in the used market at very reasonable prices. You just dive the critters like a single with an H valve.
A couple of years ago I slapped together a set of twin 50s made from steel SCBA bottles. After the paint dried, I had about $100 invested, including hydros.

 

[Braunbehrens]

Dave, if you do go with a smaller HP tank, be very aware of your gas supply. Like I said, 500 psi in one of those short guys is a lot less gas than in a big tank.

I tend to think that one shouldn't sacrifice in water performance for surface comfort. If a tank feels good in the water, then I would find another solution for the surface. I use a cart to move my doubles around, for example.

I can see some situations where a small tank would be nice, such as when doing a beach dive with a long walk etc. My solution to that was to buy a boat ;-)

Anyway, your idea of renting first is a good one, you certainly don't want to spend $300 on a tank only to find that it is no good in terms of trim.

 

[DIR Tec Diver]

The previous post about not surface comfort is exactly correct. You need good tanks that allow you good trim and balance in the water. If you have the proper trim, then you will not feel or notice the larger tanks even with your height. The HP tanks will not degrade regulator performance, those comments are unbased with todays regulators.

The new special edition tanks such as the ScubaPro 232s and PSTs are excellent. I have dived with most all of them and many others, and the ones that I use now are the 15liter SP Limited Editions. I also dive in very cold water, so the extra weight of the tanks (18kg each) helps offset the buoyancy of the insulation garments. The PST 232s are also excellent, and with these tanks you don't need to worry about the linear declination in tank pressure.

One last comment. Disregard the post about a non-isolator manifold being put on the tanks to save money. ** edited by Rick ** ALWAYS use an isolator manifold with Sherwood knobs.

 

[trheeltek]

dlwalke once bubbled...
Do they actually cause premature regulator death? Thats the main knock against them that I have heard. How true is it that they stress your equipment too much.

Thanks,
Dave

Actually, as noted above the main knock against them is if you take a LP tank to the same pressure (3500 PSI), you get quite a bit more gas - why virtually no tech divers use HP tanks. As far as premature reg death, I think the concern is that when the tank is first cracked, the higher pressure will cause the reg's high pressure seat to break down faster. I don't know, there might be something to that. But, in a reg that's serviced ever year, it shouldn't matter. FYI, A guy I know who's very good at servicing regs told me to always hold down the purge on a second stage when cracking a tank to minimize the impact - don't know if that's worth anything, but I don't think it hurts.