overfilling steel tanks

[sitkadiver]

I know it was a pretty common practice for tech and cave divers back in the 70's and 80's, but how many people are still overfilling their steel tanks?

I'm too worried about the quality of my Al 80's to try it with them, but I've been pumping my 95's and LP108's up to 3200 and not having any issues. Anyone else overfilling their tanks?

Also, will it make a difference if I stop pumping with my small Bauer and switch to a set of HP banks? Thus filling the tanks more rapidly.

[Mattleycrue76]

In a steel tank I'll take every PSI a shop will give me

[Raydar]

I know it was a pretty common practice for tech and cave divers back in the 70's and 80's, but how many people are still overfilling their steel tanks?

I'm too worried about the quality of my Al 80's to try it with them, but I've been pumping my 95's and LP108's up to 3200 and not having any issues. Anyone else overfilling their tanks?

Also, will it make a difference if I stop pumping with my small Bauer and switch to a set of HP banks? Thus filling the tanks more rapidly.

Overfilling is a bad thing, against regulations, you'll get sued to the poorhouse if anything happens, etc, etc.

You don't expect people to confess on an internet forum to something like this?

I know of people who have and do overfill with no reported problem. Of course, these are folks trying to maximize their available gas and won't cry too much if the tanks fail hydro.

As far as filling from a compressor vs banks - I don't know enough about metalurgy to hazard a guess on what pressurization rates do to the metal and the expansion. Does a slowly pressurized tank last longer than a rapidly pressurized one? Does it matter in real life terms?

[sitkadiver]

when I worked at the sop I never did this. No one is using these tanks but me and I'm filling them at home. Just wondering if installing a bank system using old welding tanks is going to create too much heat to make it worth my while.

And I know most don't admit to this, but when I started overfilling, I did it increments that I thought were conservative enough to be safe.

[CaptnJack]

There's zero practical data on fill rate and tank lifespan. In my experience faster just makes it hotter and you gotta let it sit longer to get a final pressure. No matter what they all get increasingly hot the higher the pressure anyway. I have 32% banks at 2400, 3600, and 4400psi and blasting it in there is kinda pointless since it just means I'm using higher pressure banks more and have even more to top off once they cool.

I fill my 2400+, 3442, and 3500psi rated steels to between 3000-3600 at home depending on what I'm doing. Knock on wood, I haven't had one fail hydro yet.

I would never overfill an aluminum tank, the expansion characteristics are completely unforgiving of that.

[WASP7000]

I overfill my + rated LP 95's. Never above 3000 though.

[Raydar]

In my experience faster just makes it hotter and you gotta let it sit longer to get a final pressure.

Ditto.

One thing that I've noticed about having my own compressor is that I rarely fill my steel tanks over 3000. Even the 3442 rated PST tanks.

Takes longer and generally don't need the gas anyway. PP filling means that I dump gas. I'd prefer to end a dive with 1000 psi than to end with 1500 and have to dump 500. Just a cheap bastard, I guess.

[ArcticDiver]

what are you doing with the burst discs? supposedly if you don't pile them up too thick they will give way before the cylinder.

[sitkadiver]

Just putting in a higher psi rated burst disc. my steel tanks all have pro valves.

I don't go crazy with it like some of the cave divers I've heard of, and I don't push my luck at all with Al tanks.

[WASP7000]

To me, doubling up burst disks doesn't make sense. Just use a higher rated disk instead of trying to use a safety feature in a way it wasn't designed to be used by doubling them. That's dangerous.

[CaptnJack]

I still use burst disks. Burst disks blowing can be pretty much eliminated as a failure point by replacing them periodically.

[dwashbur]

We will always take as much overfill in our steel tanks as a shop will give us. We bought our LP 95's used and have always pushed them to 3000 and a little beyond. We've had them for about 3 years and they all passed a hydro last year. I don't see any problem with it, obviously.

[Jeff Kruse]

[quote="Raydar. PP filling means that I dump gas. I'd prefer to end a dive with 1000 psi than to end with 1500 and have to dump 500. Just a cheap bastard, I guess. [/quote]

What the hell are you still PPing for?

I fill my 15 year old HP PST's to 4K every time. (I need the extra gas because my "buddies" will just leave me if I run out)

[deep diver]

I've always filled my LP 95s to 3000# and have done so for years. My HP 100 and 130s to 4000. Have heard that the steel in the lp and hp are the same steel

[CaptnJack]

Have heard that the steel in the lp and hp are the same steel

They are both chrom-moly steel but aren't the same. The specs on "HP steel" have a greater carbon content and about a 20% higher tensile strength among other things.

[CaptnJack]

What the hell are you still PPing for?

No kidding, what a waste of O2 (and air)

[Old Nubbins]

Here is what I don't understand. Take plain 'ol A36 for example - cheap mild steel. It's yield strength is 36000 psi and tensile strength at break is 58,000 - 80,000 psi. Wouldn't that seem to indicate that the weak point is not the steel itself but rather the point at which the valve is installed?

[Raydar]

PP filling means that I dump gas. I'd prefer to end a dive with 1000 psi than to end with 1500 and have to dump 500. Just a cheap bastard, I guess.

What the hell are you still PPing for?

I like living in the stone age, I guess. Plus I still haven't run 220 out to the garage. Lots of good excuses including "Diving? What's that?"

I fill my 15 year old HP PST's to 4K every time. (I need the extra gas because my "buddies" will just leave me if I run out)

[/quote]

Well, when you're diving those PST100's and trying to keep up with people diving PST104's jacked to 3500, you are going to run out first.

[Jeff Kruse]

Nope, worse. They are diving 80's! 80 minute dives are not good engough for them. They need to push it out to 90+. Water temp is now 84 degrees.

[Raydar]

Nope, worse. They are diving 80's! 80 minute dives are not good engough for them. They need to push it out to 90+. Water temp is now 84 degrees.

Maybe starting working on lowering your SAC?

Which, to bring this back on topic, is one of the two (3 if you consider rebreathers an option) options to avoid overfilling your steel tanks.

1. Improve your air consumption rates
2. Get bigger tanks.

The acronym TANSTAAFL is full of wisdom.

[CaptnJack]

Wouldn't that seem to indicate that the weak point is not the steel itself but rather the point at which the valve is installed?

The "weak point" in an otherwise (no rust, pits, etc) sound cylinder is almost always the bend where the crown transitions into the threads. Localized forces there can theoretically exceed the tensile strength of the steel which is why we have VIPs and hydro tests requalifying tanks periodically. Although steel tanks rarely crack anyway, absent rust or abuse, they "fail" slowly and almost always won't pass hydro before they split. The steel ones you see failing always look like a rusty hell inside and out.

[dwashbur]

What the hell are you still PPing for?

No kidding, what a waste of O2 (and air)

Uh, what's PPing? (Aside from the reason I wear Depends under my dry suit, of course.)

[airsix]

Uh, what's PPing? (Aside from the reason I wear Depends under my dry suit, of course.)

Partial Pressure blending, where a measured amount of pure oxygen is added to a cylinder and then topped off with air to arrive at a pre-calculated EAN mixture.

[WASP7000]

partially filling the tank with 100% O2 and the rest of the way with air to achieve the desired mix.

[Waynne Fowler]

but I've been pumping my 95's and LP108's up to 3200 and not having any issues. Anyone else overfilling their tanks?

Yet...... that you KNOW of.

they do have a working pressure rating for a purpose... as much as you may hear it, and as much as we like to think they are... those ratings are not givin arbitrarily.... there are some good reasons for those limits.. yes they are conservative..
I used to bang 4k in my hp100's as a rule.. one failed the 1st hydro (miserably) the other at the next... why not buy tanks with the appropriate volume and plan around that amount?