Overfilling LP Steel Tanks -- How bad is it?

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Why overfill? If you're buying tanks, get tanks that hold what you want.

Terry

Okay, what I want is a tank that's 6.9" in diameter, is 25" tall, weighs 27 lbs, is neutral empty, and holds 85 cft of air.

What's that? A steel 72 filled to 3000 PSI.

LP steel tanks have amazing buoyancy/size/capacity ratios when you overfill them.
 
Okay, what I want is a tank that's 6.9" in diameter, is 25" tall, weighs 27 lbs, is neutral empty, and holds 85 cft of air.

What's that? A steel 72 filled to 3000 PSI.

LP steel tanks have amazing buoyancy/size/capacity ratios when you overfill them.
... Scuba Cylinder Specifications from Tech Diving Limited - 928-855-9400
Whats so special about a 25" tank that holds 85cf of air ?
(PS ... I dont see any steel 6.75" 27lb 72's that are neutral when empty )
Granted that you would add 1/2" to that diameter but for size to capacity ratio, it's hard to beat the 3442psi tanks
 
My steel 72s, like everyone else's, are 6.9" and neutral empty, and weigh 26-27 lbs. This makes them great for small doubles.

I realize I was describing basically a LP85 as well, except for the dry weight. My point is, LP tanks overfilled do offer great size/buoyancy/capacity ratios. It's also true to an extent for the HP tanks; but they are a little heavier, and they definitely are more expensive.
 
Valid point..
For me, the motivation to overfill was because I have a Yoke regulator so I don't want an HP tank.

That makes no sense at all. You don't want to put your yoke regulator on an HP tank, so you overfill an LP to HP spec, and then put your reg on it?
 
I think he is possibly suggesting that he could overfill a 2400 psi tank to around the 3000 psi range, rather than the full 3442 psi of an HP tank or the full 3600 psi of a north florida cave fill.

Of course, it still makes little sense as an LP 95 compares with an HP 130 that is very similar in size and only a couple pounds heavier. Since both hold roughly similar volumes of gas at the same 3000 psi it makes little difference, with the edge actually going to the HP 130. (108 cu ft for the LP 95 at 3000 psi compared to 113 cu ft for an HP 130 at 3000 psi.)

Generally speaking, if you dive mostly in N FL and can get 3600 psi fills, an LP 95 makes sense as it is a bit lighter (the Fabers at least) and the price point is a bit better and it holds right at 130 cu ft at 3600 psi. If on the other hand you dive mostly somewhere else and cannot get an overfill, then an HP 130 is a much better way to go. The same would apply even if you only wanted an overfill or fill to 3000 psi as getting a fill over 2400 psi in a 2400 psi tank can be difficult in most other places.

Perhaps more importantly, unless a diver has a really old reg with a really lightweight yoke, 3442 psi is not a problem. They sell 3442 psi tanks with yoke inserts for a reason - because nearly all yoke regs work just fine at that pressure.

I am a really big fan of the LP 95, but frankly if you take away the option of N FL cave fills, the HP130/E8-130/X8-130 all make a lot more sense and the LP tank is rapidly approaching dinosaur-hood.
 
Why doesn't anyone ever ask about overfilling HP cylinders? Conventional wisdom would suggest that if a LP tank is over engineered enough to withstand a 3600psi fill in a 2400psi rated tank then a 4700psi fill in a 3500psi rated tank would be reasonable as well. Not saying I advocate such fills but LP steels aren't the only cylinders you can physically put more air into.

Food for thought:
At 4700psi a HP100 holds 134cu
 
Why doesn't anyone ever ask about overfilling HP cylinders? Conventional wisdom would suggest that if a LP tank is over engineered enough to withstand a 3600psi fill in a 2400psi rated tank then a 4700psi fill in a 3500psi rated tank would be reasonable as well. Not saying I advocate such fills but LP steels aren't the only cylinders you can physically put more air into.

Food for thought:
At 4700psi a HP100 holds 134cu

I think the main reason is because it's either more difficult (eg. harder on the compressors) to generate the higher pressures or it's just not routinely done.

Overfilling LP cylinders can be done pretty much anywhere if the shop fills AL80's to 3000 psi. A few shops I've been in can barely generate the 3000 psi for AL80's, let alone the pressures to fill the HP cylinder.

But yeah I've been known to fill my HP (3442 psi) tanks to a nice rounded up number somewhere higher than 3442. :wink:
 
When are they going to come out with an HP tank the same size as the Faber LP125's that I currently use? It would be nice to be able to have 179cu ft. haha!
 
Really? Funny, I've never heard of a single incidence of a steel 72 blowing up from being overfilled. Surely this would be news worthy as fill stations would be destroyed and people would be dying. Do you have any examples, any documented case of this happening? I'd be interested in that. I'm not denying your statement, I just never heard this before.

The main reason you don't hear about it is that steel tanks fail in a different mode then aluminum tanks do. Aluminum tanks, which are in the T6 heat treat condition, are brittle and fracture, sending out small pieces of shrapnel. Steel tanks split, simply releasing the pressure with a loud noise but usually without hurting anyone. The old news media adage "if it bleeds, it leads" means that steel tank failures rarely make the news.
 
https://www.shearwater.com/products/perdix-ai/

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