Over filling LP tanks, what's the real deal?

[bamamedic]

The only place you're gonna find 3500psi fills on LP cylinders (as far as I know) is North Florida (cave diving country!). Otherwise, most places are going to fill them to rated capacity plus 10% if they have the "+".

Whether it's "safe" or not? Well, the legal answer would be "no, because the manufacturer has not rated these cylinders to that capacity". However, LP cylinders aren't really blowing up right and left, so I guess it's up to you to make that choice.

 

[Scott L]

First...To those that are providing real information...Thank you.

Valhalla and Deepstops have somewhat divergent viewpoints.

Deepstops...what is your rationale?

Valhalla...Im going to check the Faber website, but can you give me a source for your info on the 4000 psi x 10,000 cycles?

And again...thank you for the polite answers. Im a new tech diver with all of the toys, and the cards, but I'm really just getting started. I am using this website as an educational tool.

Deepstops was tongue in cheek. My information was off Fabers's web-site around the year 2000 when I purchased 6 LP Faber cylinders. That same information is probaly still floating around somewhere. To recap all the threads on the subject one camp emphatically states that unless you have a degree in metallurgy you have no business deciding for yourself the dangers of over-filling low pressure scuba cylinders.

The other camp chimes back that there has been virtually no recorded failures of steel scuba cylinders by virture of overfilling. Most of the steel cylinder failures listed on DOT's web-site are non scuba related (welding, etc.). This same camp feels the risks are minimal at best and benefits from the added gas afforded the diver. That's pretty much the whole story IMO....

 

[deepstops]

Who called the waaaambulance?

Thousands of LP steel tanks are overfilled every year in cave country and I'm yet to hear of one blowing up.

 

[irishsquid]

...Thousands of LP steel tanks are overfilled every in cave country and I'm yet to hear of one blowing up.

I seem to remember some guys (firefighters) from up around Pa. posting here about trying to blow up some out of service tanks by overfilling them. They only acheived blowing the hoses on the compressors. My memory fades, but; I think they blew the hoses at 8000+ psi or something?

 

[techintime]

First impressions are lasting impressions and while he may be a stand up guy to some, my first dealing with a representative of the MV Spree was negative. nuff said. Also, although I signed up a year ago, I hadn't really looked around or posted anything until about a month ago. Hence I have not been around to see the same subject come up repeatedly. I will start to use the search function though before I step in it again.

Back to the subject at hand. In my training my instructor worked with a shop that filled his LP tanks to 3500psi and he taught that it was safe and permissable. In the 18 months since then I have purchased a set of LP 95s and have run into a perponderance of opinion against such fills. Hence my question. I knew that there was a variety of opinion out there and was hopeful to get some well-thought-out arguments (pro and con) that I could use to form my own opinion on what to do with my LP 95s.

And in a similar manner to throwing away the never ending credit card offers that come in the mail, if someone has seen a certain subject before, then why not just pass it by and forgo the sarcasm.

 

[Wookie]

I seem to remember some guys (firefighters) from up around Pa. posting here about trying to blow up some out of service tanks by overfilling them. They only acheived blowing the hoses on the compressors. My memory fades, but; I think they blew the hoses at 8000+ psi or something?

When a company like Compair/Mako builds a containment fill station, they have to test one of a design with a cylinder in it to failure. Seems to me the last test results I saw was that the aluminum 80 let go around 7800 PSI, and the steel 72 around 9,000. The blast door was wasted, and inoperable. The steel cylinder was relatively intact, the neck/valve came apart.. If you'd been standing next to the fill station when the steel let go, you'd have been safe. And a raccoon would have been able to crawl inside your butt with room to spare, I'm sure.

 

[Scott L]

techintime,
Fill-Express, a very technical dive shop in Pompano Beach, FL has a nice peice on all things related to scuba cylinders. Also, you are more inclined to find an LDS to overfill if you allow them to visually inspect the cylinders....

How to Select a SCUBA Tank - Dive Gear Express

 

[irishsquid]

... And a raccoon would have been able to crawl inside your butt with room to spare, I'm sure.

That cracks me up.

 

[skdvr]

When a company like Compair/Mako builds a containment fill station, they have to test one of a design with a cylinder in it to failure. Seems to me the last test results I saw was that the aluminum 80 let go around 7800 PSI, and the steel 72 around 9,000. The blast door was wasted, and inoperable. The steel cylinder was relatively intact, the neck/valve came apart.. If you'd been standing next to the fill station when the steel let go, you'd have been safe. And a raccoon would have been able to crawl inside your butt with room to spare, I'm sure.

Damn I would love to see a video of that test....

EDIT - Here there are...

Phil

 

[oxyhacker]

The 10k cycles to 4000 psi thing was in the OMS catalogs. Not sure if it originated with OMS or Faber, or if they still publicize that figure. But it didn't originate with them - it's the standard test sequence that the DOT requires for most new tanks. There's no magic to the 4000 psi, it's just the hydrotest pressure for a 2400 psi marked 3AA tank, and the DOT requirement is that the tank be able to survive 10k cycles to the hydrotest pressure.

The funny thing is that 3AA tanks like the OMS Fabers aren't required to be tested this way! They can be approved on the basis on the math alone. Which says to me that the DOT has a lot of faith in how conservative the 3AA spec is.

The other thing to note is that the test is done hydraulically with the tank filled with oil or water, and cycled very quickly. It doesn't seem to relate directly to how the tank will fare in the real world - the 6351 bad alloy tanks passed the same test, only done to 5000 psi, and I don't think anyone would argue they should be overfilled!

First...To those that are providing real information...Thank you.Valhalla...Im going to check the Faber website, but can you give me a source for your info on the 4000 psi x 10,000 cycles?