Help to identify HP steel tank (USDiver/AquaLung HP3.5)

[PriusDrIVER]

I have come across what appears to be a great buy on a pair of HP steelies, but the seller hasn't used them in quite some time and doesn't remember the size.

The details on the tank are:
DOT-E9791-3500 TP5250 3-98
1A 632684R
81

From what I can find in searches the 3500# USDiver tanks were primarily made by PST and from the dimensions of the tank (if I trust the seller to measure height correctly) it would appear these are 100CF (via specs on http://www.huronscuba.com/equipment/scubaCylinderSpecification.html). I don't understand what the "81" refers to, I wouldn't think that indicates the capacity in CF.

Are these decent tanks? I have read about them having a different size neck thread/hole limiting valve choices...and they are "spun" instead of stamped. Beyond that, are these decent tanks? If I can get a pair of them for less than a single new XS HP tank, is that reasonable?

Thanks in advance for your input.

 

[WSimington]

well the 100cf is 100 cubic feet. If the tanks pass hydro and visual inspection it would depend on what they want for them. compare the asking price to that of a new tank at your local shop.

 

[Packhorse]

Do they come with valves?

 

[PriusDrIVER]

Yes, they have valves. I just saw that listed as the downfall of these cylinders, that they can only be used with 300-bar valve that is hard to come by.

They do have valves, they currently have pressure in them. They were only used 3-4 times and appear to be in great shape from what I see in pictures. I just wanted to make sure there wasn't anything severly wrong with the 3500psi tanks that I should be aware of.

I realize they are due for hydro and vis, and will have them do a O2 cleaning on it for nitrox use.

Thanks for the feedback.

 

[spectrum]

I have a pair of those about 1 month newer and 4000 higher in serial number.

They are nice tanks with virtually the same properties as the E7-100s. Being true HP cylinders they must be used in the DIN configuration. The small neck does limit valve availability.

The biggest downside I know of is regarding tumbling for rust. If rust is discovered some shops will choose not to try timbling and reinspecting due to the difficulty in working through the small opening. This could be a long term risk or at least a PITA while you find a shop that will deal with the challenge.

Given the above, them being a genration behind and PST's staus I'd shoot for a bargain. I was happy to get my pair 1 year ago for $150. each with fresh hydro and VIP.

Pete

 

[PriusDrIVER]

Pete (spectrum),

Thanks for the info. Are yours branded as USDiver/Aqua Lung? Its hard to find info on the ones that are branded as such, seems there may have been more than 1 cylinder manafacturer that was used depending on when it was purchased. I see areas stating they were PST, others saying Sherwood.

I'll call my local shop and see if they have any experience with these tanks, hopefully its not an issue. As for valve sizes, the thread that discusses the other true HP cylinders (Asahi and Luxfer Ltd) list the 3500# models as having 7/8" inlet, where other "standard" tanks are 3/4"...if this is the case, wouldn't that actually be a slightly larger hole of just non-standard threading and diameter? Perhaps I don't understand how this is measured on cylinders. Its too bad no documentation from AquaLung seems to exist online for these.

When I purchased my Apeks XTX regs I went with the DIN model (with a yoke adapter) due to plans of using HP cylinders.

 

[PriusDrIVER]

Well, I found part of my answer. In regards to thread sizing:

Still, the most common thread form used with SCUBA cylinders and valves is the American National Standard Free-Fitting Straight Mechanical Pipe Thread also known as NPS. The specific thread form used with most SCUBA cylinders is named 0.750-14 NPS, often referred to as "3/4 NPS."
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When Pressed Steel Tank Company began manufacturing the modern 3500 psi service pressure SCUBA cylinder, they elected to use a more modern thread form for the neck opening known as Unified National Standard Fine. The specific thread form used with the steel 3500 psi SCUBA cylinder is named 0.875-16 UNF, often referred to as "7/8 UNF."
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It's very important to understand that the 3/4 and 7/8 slang descriptions do NOT indicate relative sizes of the physical dimensions of the opening! This is because the two thread forms are from two different standards. The 3/4 NPS opening is visibly larger than the 7/8 UNF opening.</quote>
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From: http://www.diveriteexpress.com/library/valves.shtml

 

[rjack321]

The sherwood and USD rebranded HP tanks were both made by PST. They are not spun clyinders and that's not very important anyway.

Oddly enough for neck sizes, 7/8" is SMALLER than the now standard 3/4" I forget why, but 7/8" is actually about 1/2" in reality.

You can still buy valves, try dive-rite express or TDL.

Working through the small hole really isn't a big deal and you'll probaby only need them tumbled occisionally anyway - assuming you don't get water in there.

If the galvanizing is good, VIPs are ok, and the price right there's no reason to not to buy these tanks.

 

[ClevelandDiver]

I am fairly certain that the E-9791 exemption is specific to PST tanks only. They can be sold under other names, like Aqualung, but that E series designation is unique to the PST high pressure steel tanks. The early E series had 1/2" valves and were rated to 3500 service pressure, the newer ones had a 3442 psi service pressure and 3/4" valves. Basically the same tanks, as they use the same exemption number.

FYI - do some searches on the board about PST and the concerns about their continued existense. Not trying to scare you, just want you to have all the info before you buy. I own a couple of their E series tanks as well.

http://www.scubaboard.com/showthread.php?t=163072&highlight=PST+exemption

http://www.scubaboard.com/showthread.php?t=159571&highlight=PST+exemption

http://www.scubaboard.com/showthread.php?t=146807&highlight=PST+exemption

 

[PriusDrIVER]

So I may have found a bit more of my answer, a history lesson of sorts I suppose.

PST created renewed interest in steel cylinders by introducing high-density 3500 psig steel E9791 cylinders in 1987. Those cylinders were sold by Sherwood (Genesis) and US Divers Co (HP3.5). US Divers held a sales exclusive for this cylinder during 1997. By 1998, that cylinder type was distributed in several volumes by other companies.

From: http://divemar.com/NAUI/docs/sources/cylinder-history.html
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