51 replies to this topic

[intotheblue]

I will say this...I got a 'cave fill' to 3600 psi in a tank last year on our annual Florida trip and it blew an o-ring in my first stage out. It ruined my dive...could have seriously hurt me if it had happened in the water and it almost ruined my second dive of the day. (I had to use borrowed gear which is never a preferred way of diving!) So in my book...serious overfills are not safe and they are not desired. I like my gear just as it is WAY too much to risk losing it over an 'overfill'.

I'd rather carry a bigger tank or a safety stage if I am worried about having enough air/gas to dive with.

Well that is why we educate ourselves and make informed decisions. I don't like to go on -- my buddy/instructor/mom told me so -- so it must be true.

That said -- I don't know that you can really blame the o-ring failure on the high pressure fill. It was likely a coincidence. O-rings go when they go. And it could happen at 2640 as well as at 3600. You don't use special regulators for HP tanks and LP tanks -- other than DIN instead of yoke on HP of course - but the innards past that are the same.

The regs had just been serviced for the trip and they are rated for 3000 psi. So 10% over that is 3300. I had a fill of 3600 and it was clearly the fill issue. When I took it in for servicing I was told that I must of had a overfilled tank as it blew the main body o-ring that seals around the shaft of the piston.

I do dive older regs but even newer regs are only slightly more capable of handling higher pressures but they are not rated that way for liability purposes.

Depending on the age of your "older" regs, there can be a pretty significant difference in their ability to handle higher pressures. Do you use "DIN"?

O-rings don't only "go when they go"... having an unequal pressure applied to the "sealing surfaces" can cause an o-ring to blow or extrude through even the tiniest of spaces. I had a neck o-ring extrude when a buddy picked up my cylinder from hydro and filled it without making sure the valve was secure in the tank. Brand new o-ring... bad application.

[captsteve]

I own several old 72steelies and i can say that at Ginnie spring last feb, they overfilled both.the burst disk started leaking in one of them and the neck o-ring blew in the other. I would not choose to put a cave fill in either.
However, I also own a new set of faber lp85s, a new faber lp120 and lp108. I would have no reservations about putting a cave fill in any of those and have. When i was selecting new tanks, my Lds specifically recommended the Fabers over some of the other steel brands because they could be safely overfilled. I also puchased high quality regs (APEKS 200) with din. It is my understanding that the din fittings are better for high pressure, but i dont know enough about the argument.
I have become friends with the tech who works on regs for the LDS. On cave fills and lots of use, the mares and lots of other brands need to be rebuilt once a year, and he explaind most of the parts that wore out, but i didnt follow that part of the conversation. the apeks and some of the other brands fared better.........yes i know they should be seviced every year regardless.

[intotheblue]

I own several old 72steelies and i can say that at Ginnie spring last feb, they overfilled both.the burst disk started leaking in one of them and the neck o-ring blew in the other. I would not choose to put a cave fill in either.
However, I also own a new set of faber lp85s, a new faber lp120 and lp108. I would have no reservations about putting a cave fill in any of those and have. When i was selecting new tanks, my Lds specifically recommended the Fabers over some of the other steel brands because they could be safely overfilled. I also puchased high quality regs (APEKS 200) with din. It is my understanding that the din fittings are better for high pressure, but i dont know enough about the argument.
I have become friends with the tech who works on regs for the LDS. On cave fills and lots of use, the mares and lots of other brands need to be rebuilt once a year, and he explaind most of the parts that wore out, but i didnt follow that part of the conversation. the apeks and some of the other brands fared better.........yes i know they should be seviced every year regardless.

sounds like you got a good set-up. I wouldn't be worrying bout the old 72's burst disks... I'd be worrying more about the cylinders... seems everyone worries bout them... I'm onlyspeaking from others' "pucker" factor.

The din issue is the captured o-ring, making it more difficult to "break that sealing surface". A yoke reg is easy to dislodge compared to a din where you have to get all of those threads to allow movement and break the seal.

Good night all...

[PerroneFord]

Man, what a fun topic!

By the way, I just filled out the PSI form for two tanks I am taking diving tomorrow. Both with mild overfills. One with Original Hydro in 1981, the other with original hydro in 1971.

Both passed hydro last december. Both tanks were used in academic environments meaning they were probably filled hot, filled over capacity, and filled 3-5 times per week if not more.

I have over 5 dozen steel cylinders at the shop, most older tanks, nearly all seeing a steady diet of cave fills, all in hydro. Cave Excursions fills more cave fills a WEEKEND than most of your LDS's in other areas have done in their lifetime.

Until I see some evidence that these tanks are having trouble dealing with the fills, I'll keep on with the 3300-3500 psi fills. As for the 4000psi fills, damn few people do it these days. With the advent of the 130s, you don't need to pump the 104s up like you used to. Staging is also more prevalent than it used to be in the old days. And anyone SERIOUSLY exploring caves these days is generally on CCR or SCR.

[drbill]

My #1 dive buddy Andrea has a white composite tank rated (I believe) at 4300 psi. It requires hydro every 3 rather than 5 years,

[Big O]

My #1 dive buddy Andrea has a white composite tank rated (I believe) at 4300 psi. It requires hydro every 3 rather than 5 years,

And where does Andrea use this tank Bill? Firefighter? Im a Vol. Fireman and we use them, but I think ours have a finite lifespan of say 10 years, along with the shortened hydro span.

[BradfordNC]

Burst disks letting go are no picnic either, so don't think of a blown burst disk that as an acceptable result. If you have overfilled, you are clearly the one responsible, and should be held liable. Note I did not say "could", I said "should" and I mean it. That includes manslaughter charges if someone is killed.

oh i know. saw at least 2 burst disks give out at the fill station over Memorial Day weekend.
the horror
the horror
the horror

i'm still having nightmares. i'm gonna call the doc to arrange therapy for PTSD
all that whooshing, the water in the fill tank getting sloshed out, and to think, all that yummy Nitrox 32 being wasted.

good thing the tank monkey was able to turn the isolator valve in time to prevent a total loss of gas.

a burst disk is part of a safety assembly. when it ruptures it is contained by the bolt holding it in place.

if someone is killed when a burst disk ruptures??? wow, what are they doing at the time? do they have their mouth over the plug? i'd like to see the Rube Goldberg contraption from that.

With 150 HP tanks available, you really have to be doing some extreme diving to need to resort to cave fills.

extreme diving?
hmmmmm, do you mean like cave diving? so maybe its cave divers getting these cave fills??? you might be on to something.

and those 150's your talking about are simply 108s with a "cave fill"

Tank explosions are rare, but they do occur. If they did not occur, we wouldn't need VIPs or Hydros.

so tanks with VIPs and Hydros don't explode? it's just the tanks without VIPs and Hydros?

I'm not sure what you would consider convincing evidence, but there are photos and stories on the Internet.

the internet you say?
indeed.
nuf said

You might also want to read the book Shadow Divers, which is about Chatterton and Kohler's efforts to identify the U-Who. Chatterton had a tank explosion in his garage. Fortunately, no one was there at the time, but the damage was considerable.

read it. it wasn't a scuba cyclinder. and someone else already addressed this issue.

Why not believe that? Factories all over the world make different grades of the same product for different markets. If they can get away with using cheaper materials or a cheaper process to make goods for one country they do. IE: baby clothes have to be flame retardant to a degree in the US, not so in Mexico I know from first hand experience that plants will run a different line of material to make the baby clothes for export.

ok, i'll give ya that. but there is a big difference between a mill that turns out babyclothes and the factories that smash out steel tanks.

If a tank is rated for 4400 psi, then go for it, but I am not aware of any such tanks being available in the US. HP tanks are rated to 3442. I wouldn't call 3500 or 3600 a "cave fill".

actualy, according to DOT, its not HP until the rated pressure is over 3500. 3442 is not HP. the valves used in tanks rated for 2640 psi tanks are the same as those used for 3442 psi tanks. tanks rated for 3500 and over have different neck threads and require a different valve.
as far as what you would call a cave fill or not, are you a cave diver?

Cave fills as I understand the term are boosted way beyond the rated capacity.

hmmm, i'm guessing your not.

the term comes from the practice of overfilling tanks rated at 2640 psi. so yes, 3600 psi is a cave fill.

As for burst disks, the same idiots that go for cave fills tend to double the disks.

i'd imagine that the same idiots who go for cave fills are probably cave divers.
they make burst disks which are rated for pressures around 3600 psi, these are the burst disks place in your tanks which are rated at 3442 psi.
the burst disk rating is higher than the tanks fill rating.

double disking is soooooooo last century.

Actually, overfilling tanks for no valid reason doesn't make a whole lot of sense. It does cause extra wear and tear on your compressor too. I will routinely "cave fill" my appropriate cylinders for cave diving. There is a reason they are called "cave fills"...

for no valid reason is right. just to have a small bit of extra air on a recreational dive is not a valid reason.
wear on the compressor would depend on the size and type compressor you have.
but like ya said, cave fills are for cave diving.

there are a few on this board who prolly remember when it was hard to get a compressor to push over 2600 psi. hmmmmm, prolly the reason tanks came rated at 2400 psi with an allowance for a 10% overfill.
it was hard to get a fill to 3000 psi.
but with the popularity of diving and the aluminum 80, there was an increase in sales of compressors pushing 3000 psi.
hmmmmm

I also understand that the LP tanks that are manufactured for sale here are the same as those in Europe and that the hope in so doing is that the DOT will eventually allow a higher pressure rating on the cylinders already in production for sale here.

this is what happened with PST's E series tanks. to bad PST went out of business.
but worthington and faber are both selling tanks using the DOT Exemption that PST used.
no difference in tanks, just an exception to the rating.

For recreational "no-deco" diving, "poking" around the reefs, snapping a pic or two... an aluminum 80 with the typical 2700 to 2900 psi you get at the LDS is just fine.

no need for extreme air unless doing extreme dives. agreed

Of more concern is the speed at which my tanks are filled... and how hot they get in the process.

true true.
that is where the real "wear and tear" on the tank is coming from.

I own several old 72steelies and i can say that at Ginnie spring last feb, they overfilled both.the burst disk started leaking in one of them and the neck o-ring blew in the other. I would not choose to put a cave fill in either.

around that area you have to tell them if you don't want your tank filled past a certain point. they pretty much give any steel tank a cave fill unless you say otherwise.

As for the 4000psi fills, damn few people do it these days.

most of the 4000+ psi fills were done using composite tanks which were rated for those pressures during the research diving at Wakulla Springs. it was a government funded/sanctioned project and wasn't some shmoe overfilling tanks in his garage.

[intotheblue]

most of the 4000+ psi fills were done using composite tanks which were rated for those pressures during the research diving at Wakulla Springs. it was a government funded/sanctioned project and wasn't some shmoe overfilling tanks in his garage.

Oh, so now I'm a shmoe...

Soitenly!!! yuk, yuk, yuk...

[BradfordNC]

Oh, so now I'm a shmoe...

Soitenly!!! yuk, yuk, yuk...

hey now, i wasn't naming names or pointing any fingers, but if the shoe fits ....... lol

4000+ psi fills in your garage huh? no wonder your compressor wore out

lol

[PerroneFord]

As for the 4000psi fills, damn few people do it these days.

most of the 4000+ psi fills were done using composite tanks which were rated for those pressures during the research diving at Wakulla Springs. it was a government funded/sanctioned project and wasn't some shmoe overfilling tanks in his garage.

I've got one of them. They're very pretty.

This was a fun read.

[intotheblue]

Oh, so now I'm a shmoe...

Soitenly!!! yuk, yuk, yuk...

hey now, i wasn't naming names or pointing any fingers, but if the shoe fits ....... lol

4000+ psi fills in your garage huh? no wonder your compressor wore out

lol

I don't remember ever going over 3700, personally... fellow shmoe... and so far, the compressor is fine. But, I don't fill that high unless I have a good reason.

[Geek]

Well I seem to have drawn a few shots so I guess I need to respond. First I am not a cave diver. It is possible that I misunderstand the term "cave fill", but so far I don't think a precise definition of a cave fill has been offered. My understanding of the term is filling a cylinder far beyond its rated capacity, e.g. taking a low pressure steel cylinder rated to 2400 to 2600 and boosting it to 4000. This would not include the practice of filling the tank a couple hundred psi beyond full expecting it to be at about the right pressure after cooling. If someone wishes to offer a different, or more precise, definition, then please do.

Regarding the term "high pressure", I am using the term as it is used for scuba tanks, e.g. PST Series E tanks and similar tanks from other manufacturers. I believe my usage should have been clear from the context.

Regarding some of the higher pressure cylinders mentioned, I have heard of composite cylinders that can handle 4000 psi or more, but I have not seen one intended for scuba. In addition, my understanding is composite cylinders are very buoyant and have a limited lifespan. If someone is aware of a composite cylinder intended for scuba, I would be curious to know make, model, rated capacity, and buoyancy characteristics.

I grant that the likelihood of a cylinder explosion is small, even with a "cave fill". On the other hand, the effect of a cylinder explosion is sufficiently catastrophic, that I personally would get a cylinder large enough for the gas I needed before pushing my luck in this fashion. As for burst disks, they are intended to let go before the tank does, which generally means they will let go at some pressure above 4000 psi, so if the disk goes, the tank is already way over rated capacity. If you double the burst disks, it is not longer clear what will fail first.

With tanks as large as 133 cf widely available, I don't think that significantly overfilling tanks can be easily justified. If you need more gas, get a bigger tank, or take an additional tank.

For those I offended by calling those who persist in significantly overfilling tanks "idiots", I apologize. However, I would appreciate it if you would name me as a beneficiary in your will.

Edited by Geek, 05 June 2006 - 06:14 PM.

[scubafanatic]

Regarding some of the higher pressure cylinders mentioned, I have heard of composite cylinders that can handle 4000 psi or more, but I have not seen one intended for scuba. In addition, my understanding is composite cylinders are very buoyant and have a limited lifespan. If someone is aware of a composite cylinder intended for scuba, I would be curious to know make, model, rated capacity, and buoyancy characteristics.

...might want to check out this link:

http://www.luxfercyl..._imperial.shtml

Karl

[Desert_Diver]

<snip>
Regarding some of the higher pressure cylinders mentioned, I have heard of composite cylinders that can handle 4000 psi or more, but I have not seen one intended for scuba. In addition, my understanding is composite cylinders are very buoyant and have a limited lifespan. If someone is aware of a composite cylinder intended for scuba, I would be curious to know make, model, rated capacity, and buoyancy characteristics.

There's a northern European company selling composite scuba tanks for the military, and they got a HUGE order not long ago (can't find the bookmark right now). I'd heard that both Luxfer and Worthington made 'em as well, but I don't see it in the stuff I have saved here. 'Least not for diving, that is.

The company is Interspiro in the Netherlands, brief info HERE for their composite scuba tanks.

I think the real problem with the DOT lifetime is purely 'cos they don't have enough years of experience with them, yet. Give 'em another 20 years worth of data and they'll probably push the number up. Nobody ever accused the DOT of being fast. Our Tax Dollars (not at work).

Edited by Desert_Diver, 05 June 2006 - 07:12 PM.

[PerroneFord]

I'll try to take a picture this week of the Luxfer Composite Scuba Tank we have. I don't know the buoyancy characteristics, but it's VERY buoyant.