HP vs. LP / High Pressure versus Low Pressure steel tanks

[bigcat]

Got it. So simple if I had only thought about it for a moment! Thanks. Your right, the larger tanks wouldn't really pose a problem for me. Thanks Pug!

 

[bigcat]

Hey NetDoc, thanks for input. I noticed your a member of the bungied wing coalition. I just posted a new thread on the BC site. Having trouble with my OMS bands.

 

[Scottri]

I prefer LP tanks because I always get a good fill. I have used HP tanks and gotten crappy fills from some shops.



Scott

 

[devjr]

PST's galvanized HP tanks are almost too good to be true. That's why nobody outside the USA can duplicate them. The only trim problem I've seen is running before a current. The flow sometimes pushes up under your legs and creates a slight lift. Weight belt takes care of it.

 

[Thomas Ivey]

Lets clear up a couple of issues here:
· Retesting plus rated tanks known as DOT-3AA, the plus rating can be re-applied for the life of the tank as long as it passes the protocol for a plus rated tank. Most re-testers are ill equip with the proper equipment and knowledge when it comes to this process. To aid in this issue new scuba tanks will have the REE# stamped in the shoulder of the tank.
· HP tanks putting stress on regulators, I would always check with the manufacture of your reg. Any reg that is able to have a 300 DIN adaptor installed on it is able to operate at a working pressure of 4350 psi. This was a issue back in 1988 when PST debute the first 3500 psi scuba tank, but does not seem to be an issue currently.
· HP tank design, with the advantages of much shorter overall length based on volumes, and excellent weight to volume ratios. I see the HP design to have all of the advantages that a divers is looking for, as long as your LDS can fill it.

 

[devjr]

Tom, welcome back. I agree, from an engineers point of view the HP is superb. Some divers prefer the longer, heavier LP tanks for their own reasons, and PST offers a commensurate product line.

The only gripe I have is that high pressure, high capacity HP tanks are only offered in 7.25 inch diameter. Your company used to sell a negatively buoyant tank which held 94 cf at 3300psi, and was the same size and length as the old standard 71.2 (which you also sold at one time).

I'm not even going to mention the competitions' eight inch diameter water heaters. Oops.

 

[bmazin]

One tank I've been looking at for a set of small doubles is the scubapro (faber) medium pressure (3000+ = 3300 psi) 72 cf tank. Seems like a good compromise. Anyone have any experience with these tanks? What about doubling them up?

Ben

 

[devjr]

I believe that SP's 72 is a Faber rated 72 cf @ 3000+ and is 6.75 X 20, -3.7 neg. It appears that PST makes a similar tank; 72 cf @ 3300, 6.9 X 20, -6.0 neg.

http://www.huronscuba.com/gear/cylinders.htm

 

[devjr]

Before you jump to conclusions you should know that the Aqua Aire HP 3500 is available in a LONG, 120 cu ft version. At 3000 psi it holds 102 cu ft, with "overfill" capacity up the wazoo.

Oops, there go all your calcs and Pug's objections.

 

[Uncle Pug]

Originally posted by devjr
Oops, there go all your calcs and Pug's objections.

Long is good for the big fellers but....
Still object to:

Capacity vs. ease of filling mixed gas/nitrox.

Yes a HP 120 filled to 3000 psi will give you almost the same cf as a LP 104 filled to 2640 psi but if you can't see that there is a BIG difference there then I can't enlighten you further.

Yes a HP 120 can be filled to 3500 psi to give 120 cf but a LP 104 filled to 3000 psi gives almost the same... but ~ gasp ~ we would never do something as dangerous as that. If you can't see that 3000 psi is much easier to fill that 3500 psi then I can't enlighten your further.

No - a HP120 shouldn't be stuffed with more that 3500 psi so we will stop there and I won't even mention the unmentionable about LP 104 stuffing.

The point being that for mixing gas, lower final fill pressure is desirable and if you are not mixing gas why in the world would you need that kind of capacity anyway? Who needs 120 cf of AIR for a single tank dive???