Using "fuller" tanks.

[victorzamora]

Please don't hold back..... tell us how you really feel about yoke divers.......

Hahaha, it's just me picking at Storker. My only issue with Yoke divers is that so many rental tanks are yoke only, which is sad when I travel. Otherwise, I couldn't care less what you dive. From a strictly engineering perspective, it's unbelievably clear that Yoke is drastically inferior to DIN. But with infrastructor the way it is and all that, it'd be hard to change quickly. It's just crazy that yoke-only valves are still being made.

I thought LP tanks were always supposed to be filled to 3800? Sheesh, you guys and the light fills.

3800 is a "good fill." 3600 is normal, and 3400 makes me sad. 3800 is starting into the Van Der Waals effect arena, so much above that and you start really getting diminished returns. But I agree with you, I want a hydro test with every fill

 

[kelemvor]

Hahaha, it's just me picking at Storker. My only issue with Yoke divers is that so many rental tanks are yoke only, which is sad when I travel. Otherwise, I couldn't care less what you dive. From a strictly engineering perspective, it's unbelievably clear that Yoke is drastically inferior to DIN. But with infrastructor the way it is and all that, it'd be hard to change quickly. It's just crazy that yoke-only valves are still being made.

I bought DIN when I started buying gear in large part due to feedback I got here on scubaboard. Most of the time it's a non issue. Yoke adapters kind of suck though. I had to use them twice a week for over a year when I was working at the clearwater marine aquarium. I converted my regulators over to yoke rather than bringing adapters for my upcoming trip to Cozumel with the scubabord group. Switching the regulator back and forth really is pretty simple to do.

 

[Storker]

I bought DIN when I started buying gear in large part due to feedback I got here on scubaboard.

Around here, yoke is only seen on the local Craigslist equivalent, when someone has cleared his garage and thinks he's got to get SOMETHING for his obsolete gear.

We still have a yoke-to-DIN fill adapter at our club, but I doubt it's been used the last 5-10 years...

And, BTW, I've never had an issue with getting a 300 bar fill.

--
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Typos are a feature, not a bug

 

[Carl_F]

. I converted my regulators over to yoke rather than bringing adapters for my upcoming trip to Cozumel with the scubabord group. Switching the regulator back and forth really is pretty simple to do.

When I was diving in Coz early last year all the tanks had the yoke inserts which could be removed. Heck, as far as I could tell they never did change an oring. Everytime I asked to change the oring on the tank, they just grabbed the allen wrench and swapped out the insert from another tank. I'd have used up my whole save-a-dive kit if I had used my orings.

 

[emoreira]

Instead of thinking in a single tank with 4500 psi, why not a double with 3000 psi each ?
Fills will be cheaper for 3000 psi than for 4500 psi.
If you think of a 80 cuft tank with 4500 psi, you are also thinking of deco dives.

 

[Mr Carcharodon]

A bit of a spin off from the multiple threads asking what tank size to use.
Given the improvements in material quality over the past 40 or so years why are we still sticking with our tanks pressure restricted to 200 bar 3000psi or thereabouts?
Are there compressor limitations in play as well as first stage/burst disk etc?


sorry folks-yep 200bar /3000psi -not 200psi as I typed

It seems that over the past 30 years material properties have not changed a lot at least for the types of materials you will typically find in scuba tanks. So there is not really a materials driven opportunity unless you go to something other than steel or aluminum. There are higher strength steels and non-ferrous materials out there but they are brittle and might not have graceful failure modes.

This is not compressor drivien. On at least one occasion I have received over a 4K fill on an aluminum tank no less. Pretty routinely at the local shop where most of the time the customers are running the booster the practice is to fill to 10% over the nominal fill pressure (3800-3900) which gives the desired 3500 psig after cooling. And this is not burst disk driven since often you can stack more than one. This is likely market driven in that there is not a lot of demand that is not met by larger steel tanks or doubles. The larger double tanks start to imply decompression diving and high fill costs (helium). There are some people out there doing that but probably not enough to change what the tank manufactures do.

 

[rx7diver]

I was a still-new diver when the PST HP 3,500 psig cylinders were introduced ca. 1988. The tank material used is a newer steel alloy, rather than a thicker AAA or AA steel. So, these tanks have thinner walls and are lighter in weight, even though they have a higher working pressure. At the time 2,250+10% psig PST 72's were common around here, as were 3,000+10% psig Scubapro (Faber) cylinders.

I immediately special-ordered the first HP 80's seen in this area, absolutely clueless about buoyancy considerations. These little tanks (20" height, 7.25" OD, 27# empty weight, iirc) were like little jewels at that time, and were amazing to behold, indeed! They made quite a splash around here, pun intended. I still own them, still dive them, still love them.

The idea of smaller scuba gear has always interested me. I would absolutely love a smaller, lighter (in empty weight), ~80 cu ft cylinder—even if its buoyancy characteristics are less than optimal.

I remember becoming extremely excited in the early 1990's about a new cylinder that was coming to market. An importer was promising to sell some Russian-sourced, titanium cylinders here in the US. Two sizes, the smaller being rec-diver sized (~80 cu ft, with a smaller than 6.9" OD, and a working pressure even higher than 3,500 psig, iirc). Unfortunately, the cylinders were never offered that I know of.

I lust for a double hose regulator. I salivate every time I read about the VDH Kraken. However, it is the antithesis of small scuba, and this (along with the fact that I already have so many regulators that I can't keep them all properly exercised) prevents me from writing a cheque to VDH today and ordering a Kraken and a VDH backplate.

Safe Diving,

rx7diver

 

[Storker]

If you think of a 80 cuft tank with 4500 psi

Are you talking about an Al80 sized tank pumped up to 4500? In metric that would be like an 11L 300 bar.

you are also thinking of deco dives.

Not necessarily. Not at all.

A 300 bar 11L tank would hold almost exactly the same amount of gas as a 200 bar 15L, which is the classic rec sized tank over here.

--
Sent from my Android phone
Typos are a feature, not a bug

 

[rx7diver]

A bit of a spin off from the multiple threads asking what tank size to use.
Given the improvements in material quality over the past 40 or so years why are we still sticking with our tanks pressure restricted to 200 bar 3000psi or thereabouts?

The idea of smaller scuba gear has always interested me. I would absolutely love a smaller, lighter (in empty weight), ~80 cu ft cylinder—even if its buoyancy characteristics are less than optimal.

Spent some more time thinking about this issue of smaller, fuller scuba cylinders. What physical dimensions would I, myself, prefer?

1. Length: 24" (e.g., the length of a PST 3,500 HP 100) or 25" (e.g., the length of an old-school PST 2,250+10% 72). This length is long enough to both "sit well" (i.e., I can easily slip into my harness or BC while seated on a dive boat bench or tailgate or van trunk, without gymnastics/contortions) and "wear well" (so the bottom of the cylinder rests on my derriere rather than in the small of my back).

2. Outer diameter: 6" (e.g., the OD of a "slim-line" Scubapro Faber 60.6 or 71.4). Extremely hydrodynamic, as this OD presents very little cross-section to the water. But still wide enough so that it can be stood up (on its boot) without easily falling over, even when wearing a Scubapro Stab Jacket BC or Freedom Plate+harness and reg. (The OMS Faber 46 and 50, having an OD of 5.5", are, perhaps, too skinny for this).

3. Empty buoyancy: ~Neutral (with valve) when empty in salt water.

4. Capacity: ~80 cu ft at service pressure. EDIT: Air weighs ~0.074 lbs/ft^3 at sea level (at 80 degrees F), so 80 cu ft weighs ~6 lbs. The corresponding buoyancy swing can be accommodated relatively easily by many experienced, practiced divers using only their lungs.

5. Empty weight: No more than ~25# empty (with valve).

6. Durability: Same durability (fill cycles, etc.) as current steel cylinders, same required schedule for hydros and visual inspections.


That's about it. The service pressure of this hypothetical cylinder will necessarily (?) be greater than 3,500 psig, I think

All that's needed is for some engineer to form this cylinder using an appropriate metal!

Safe Diving,

rx7diver

 

[Diving Dubai]

Interesting thread

As mentioned above there are two main issues with higher pressure fills, cost of compressors and the laws of physics thus there is little likely hood of this being mass market.

Cylinders themselves are always interesting.

It always amazes me that there is a preconception amongst divers that Aluminium cylinders are lighter than Steel. Which is generally not the case. Obviously steel cylinders of a similar volume get more gas because of the higher pressures.

I totally understand the industries's love of the S80. It's cheap, and low maintenance - not corroding as easily as a steel (generally speaking) and of course resilient to damage.

Of corse I'm a steel fan, not that I should be. I dive in high water temps where we wear the minimum of exposure protection in the summer, we have higher salinity levels than is the norm and we have high humid temperatures. All of which are bad for steel. That said steel cylinders (12l and 15l) are by far the most prevalent here. However 99% of diving is of boats where we don't have the same weight concerns as shore divers.

We of course use the lighter weight steel cylinders for the most part to save some kilos. But generally speaking most people need some weight so it might as well be in the tank.

Now of course you could make cylinders from other materials to reduce their overall weight. For those would don't know, this is how you make an Ali cylinder and this is how you make a Steel cylinder.

Material considerations are not just for strength/weight but also for cost and ease of manufacture.

You can buy carbon fibre cylinders for rebreathers (2or 3L I think) however they are 2 x the price of a normal cylinder. Obviously if you want to reduce weight and not bothered about cost (after buying a rebreather whats another $500?) then the are the way to go. Unfortunately even if you did make them big enough, they really wouldn't be that great for general use, mainly because carbon fibre isn't as damage resiliant as Ali or steel. And when empty their buoyancy characteristics would be awful - so no use for the recreational diver.

You could use titanium, certainly it'd be lighter and stronger but a pig to manufacture. Also if you scratched it, then its likely it would fatigue quickly

You could make a hybrid sat a steel wrapped in carbon fibre - that would be lighter and could take higher pressures, but then you can't inspect the steel underneath the carbon, so limited life

At the end of the day the cylinder in a perfect world needs to be neutral is when near empty otherwise the amount of extra weight required to offset its positive buoyancy , precludes any advantages. Steel is still the best candidate for a material, although as you make a more and more exotic alloy for greater strength/reduced material you will cause huge problems in being able to manufacture it cost effectively not only with tooling but there would be a greater failure rate in manufacture.

The only benefits would be for the larger tanks. If you could get a 15l or 18l tank the same weight as a 12l steel then that might have mileage but how you go about that while allowing people to be able to abuse their tanks on a boat or in a car, and give them a decent life expectancy with a reasonable cost is possible the hardest part