LP, HP or aluminum

I am new to diving but I do want to eventually get into tek diving. I have ordered Din connection for my regulator and soon I will be buying tanks. Why do a lot of the tek divers use LP steel tanks? Why Not HP steel tanks? Why not aluminum?

ScubaDan,

You use the type of tank specific for the type of dive that you're doing. For instance, if you dive with a wetsuit, you don't want heavy steel tanks because your wetsuit will lose bouyancy at depth and your weighting will be way off somewhere on the dive. On the other hand, with a drysuit , you need steel tanks for weight. As for HP vs LP, you can actually get a much better fill with most fill stations for LP tanks. Even though the rating is lower for LP104's, we fill them to 3200-3500 lbs routinely. In cave country you'll rarely see fills lower than that.

I use LP 104's with my drysuit-single or double. I use AL 80's with a wetsuit-single or doubles.

The other thing of course is that with alu you restrict yourself to 160 cf of backgas since no one is going to overfill alu tanks, and that just isn't enough often if you are following rule of thirds and don't want to overly festoon yourself with stages. With overfilled LPs you can have 260 cf, 300 or even more. Wetsuit this is not as much of a prob since you have to be more conservative on exposures. Sure there are bigger alus but not much bigger and they are notorious floaters.

ScubaDan once bubbled...
I am new to diving but I do want to eventually get into tek diving. I have ordered Din connection for my regulator and soon I will be buying tanks. Why do a lot of the tek divers use LP steel tanks? Why Not HP steel tanks? Why not aluminum?

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Interesting that you fill a 2640 PSI tank to 3200 to 3500. This is right from the PST web sight “This series has an operating pressure of 2400 psi with a 10% over fill; maximum service pressure is 2640 psi. “ Same on the OMS web site. So you’re saying its fine to go 30% more then the 2640 recommendation.

I will be buying a dry suit for both me and the wife.

ScubaDan once bubbled...
Interesting that you fill a 2640 PSI tank to 3200 to 3500. This is right from the PST web sight “This series has an operating pressure of 2400 psi with a 10% over fill; maximum service pressure is 2640 psi. “ Same on the OMS web site. So you’re saying its fine to go 30% more then the 2640 recommendation.

I will be buying a dry suit for both me and the wife.

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Actual burst pressure is in the 5000-6000 lb range, I believe. The manufacturers are building in HUGE margins to cover their butts. Ask the cave divers if they ever see fills lower than 3400 lbs. I think you'd be surprised.

Just 'cause the speed limit says 55 doesnt mean that your car can't go faster.

From what I understand DOT is about to start bustin' a** for those who do **cave** fills. Don't get me wrong, it's nice to dbl disc & pump 'em up, but have you ever seen the aftermath of a tank that went POP! Before Branford Dive shop went under 1 of the guys was doing a **cave** fill on a set of steel dbls. What he didn't know or realize was the tank was Imperial, but the valve was Metric w/no disc. Get the picture yet?

thethumper once bubbled...
From what I understand DOT is about to start bustin' a** for those who do **cave** fills. Don't get me wrong, it's nice to dbl disc & pump 'em up, but have you ever seen the aftermath of a tank that went POP! Before Branford Dive shop went under 1 of the guys was doing a **cave** fill on a set of steel dbls. What he didn't know or realize was the tank was Imperial, but the valve was Metric w/no disc. Get the picture yet?

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Stupid is as stupid does. (I think I remember that from somewhere!). One accident from someone who didn't know what they were doing doesn't negate the fact that thousands-maybe tens of thousands of "cave fills" are done each year with no detrimental effect. If they were such a hazard, you'd have shops blowing up everywhere, and that's just not happening.

AFAIK, the incident occurred at 1800 PSI involved a single
tank. Hardly overfilling.

Putting a metric valve ( M25 ) onto an Imperial ( 3/4 )
tank is just freaking wrong and has nothing to do with
overfilling. They are different sizes for gods sake regardless
of metric valves not having burst disks.

I'm surprised the mismatched valve threads held on to 1800 PSI.

Most tank incidents occur with Aluminum BTW. I most
definately would not overfill Aluminum tanks very much
or on a regular basis.

Kell

thethumper once bubbled...
From what I understand DOT is about to start bustin' a** for those who do **cave** fills. Don't get me wrong, it's nice to dbl disc & pump 'em up, but have you ever seen the aftermath of a tank that went POP! Before Branford Dive shop went under 1 of the guys was doing a **cave** fill on a set of steel dbls. What he didn't know or realize was the tank was Imperial, but the valve was Metric w/no disc. Get the picture yet?

Click to expand...

The rating on the OMS (Faber) low pressure steels is 4000 psi in europe. It's DOT here that have put the rating on them . As was mentioned earlier in this thread, the burst pressure on these tanks is very high.

Also, just as a point of interest, back in 95 we had a local company doing fills for the sea urchin divers in the area of which I was one. While the boom was on for urchins, these guys had set up a strictly air fill station that picked up tanks, filled and delivered them back to the boats (they actually did quite well until we had a major die off of urchins) They had hundreds of thier own tanks as rentals, but would also pick up other tanks for fills.

These lunatics were routinely filling aluminum 80's to 3500 -3700 psi. They did it to mine once, never again. Luckily, they never had an accident, and went out of business after a couple years so the danger passed. It's amazing that people risk their lives for a couple hundred psi in an aluminum tank.

The LP steels though, are made to take it. We also routinely fill our OMS tanks to 3200-3500.

See you on the bottom,
Al.

I've read that the burst disk is usually rated at 1.5 time the working pressure of the tank. For a LP steel @ 2640, thsi would be 3960 psi. Why then would one need to double disk the valve to fill it to 3500? I also find it unlikely that DOT is even remotely concerned about "cave fills". Harlow says that technically they don't have any legal recourse regarding non-commercial private tanks utilized for private purposes.